{ "metadata": { "title": "Chemistry", "subtitle": "Classes Nine and Ten", "publisher": "National Curriculum and Textbook Board (NCTB), Bangladesh", "publisher_address": "69-70, Motijheel Commercial Area, Dhaka", "publication_year": 2026, "first_publication": "September, 2012", "revised_editions": ["November, 2014", "October, 2024", "October, 2025"], "authors": [ "Professor Dr. Nilufar Nahar", "Waliullah Md. Ajmotgir", "Dr. Md. Iqbal Hossain", "Dr. Md. Mominul Islam", "Nafisa Khanam", "Md. Zulfeqar Haider", "Md. Arshad Hossain Chowdhury", "Subir Chowdhury", "Md. Mamun Sarder" ], "rights": "All rights reserved by the Publisher", "distribution": "For free distribution by the Government of the People's Republic of Bangladesh" }, "chapters": [ { "chapter_number": 1, "title": "Concepts of Chemistry", "start_page": 1, "end_page": 16, "content": [ { "section": "1.1 Introduction to Chemistry", "text": "In prehistoric times, people did not know how to wear clothes, or how to build houses. Even they did not know how to cook and eat. How much people are advancing today in the age of digitalization! They are controlling heat and using it for various purposes, and eventually learning to generate electricity. So many things people are doing by using electricity! By using the internet, people can see what is happening around the world just staying at home. All these are contributions of science. As a result, naturally the question arises- what is science? Science is the systematic, orderly and continuous effort of mankind to manipulate nature for their own betterment. There are many branches of science and chemistry is one of the major branches.\n\nHere the question is- what is chemistry? The branch of science which deals with the composition of compounds composed of elements, structure and nature, properties, uses, etc. is called chemistry. It also deals with the mutual conversion or transformation of objects, and absorption and emission of energy (mainly thermal energy) during the conversion.\n\nWe know that burning coal produces heat as well as carbon dioxide compounds. Some of the examples of chemistry are the rusting of iron or iron- made objects when left in a moist environment, the extraction of medicines and perfumes from the extracts of various plants, the extraction of various metals from ores, etc. Thus, it can be said that from prehistoric times, people have been using chemistry in different ways knowingly or unknowingly. According to the information available so far, the first metal used is copper. Apart from that, people have been using metals like gold, silver, tin, iron etc. since ancient times.\n\nHumans learned to melt copper and tin, mix them and cool the mixture into another hard alloy named bronze at around 3500 BC. Bronze was used to make quality weapons. Bronze was also used to hunt animals, cultivate crops, cut fire wood etc. This alloy became an essential product of the then human race. Bronze contributed a lot to the progress of human civilization.\n\nLike bronze, people have made many alloys, including steel, and are still using them for various purposes.", "figures": [ { "caption": "Antoine Lavoisier, Robert Boyle, Sir Francis Bacon and John Dalton", "reference": "Fig 1.01" } ] }, { "section": "Origin of the word, Chemistry", "text": "In the mediaeval age, some Arab muslim philosophers tried to make gold out of cheaper materials like copper, tin and lead. They also tried to get an elixir which would lengthen the life of humans. To be successful in their attempts, they conducted many experiments. Though they failed in their original attempts, mixing different metals, they could produce different metals which would look like gold. Basically, these were the earliest attempts of systematic study of chemistry or experimentation. These mediaeval Arab experimentation with chemistry was called Alchemy and the philosophers were known as Alchemists. The term 'Alchemy' comes from the Arabic word 'Al- Chimia' which again takes its origin from 'Chemi' or 'Kimi'. The word chemistry comes from this chemi. Alchemist Jabir Ibn Hayyan is the first scientist to carried out chemical experiments in a laboratory. That is why he is sometimes called the father of chemistry. Jabir Ibn Hayyan believed all matters are composed of four components- soil, fire, water and wind. Although he researched these things, the mysteries of chemistry were not clear to him. Scientists including Antoine Lavoisier, Robert Boyle, Sir Francis Bacon and John Dalton are the first school to explore the mystery of chemistry. Antoine Lavoisier is called the father of modern chemistry.\n\nThe branch of science that discusses the structure of matter, its nature and changes is called chemistry." }, { "section": "Table 1.01: Explanation of different incidents in every day life in terms of chemistry", "tables": [ { "headers": ["Subject", "Analysis"], "rows": [ { "Subject": "A green mango is sour while a ripened mango is sweet", "Analysis": "There remain various organic acids like succinic acid, maleic acid etc. in a green mango which makes it sour. As it ripens, these acids transform into glucose and fructose due to chemical reactions and turns the mango sweet." }, { "Subject": "Burning of kerosene, natural gas and wax", "Analysis": "The main component of these elements is hydrocarbon which is a composite form of carbon and hydrogen. When we burn them, carbon and hydrogen react with oxygen in the air and produce carbon-di-oxide, vapour, light and heat." }, { "Subject": "Taking antacid due to acidity in stomach", "Analysis": "Acidity occurs in the stomach when excess hydrochloric acid is generated inside. Antacid contains aluminum hydroxide and magnesium hydroxide. These two compounds neutralize hydrochloric acid." } ] } ] }, { "section": "1.2 The Scopes of Chemistry", "text": "Wherever there are matters or substances, there is chemistry. Various gaseous elements are there in the air. There are continuous chemical changes occurring in the air. The same is there in the soil we are living on. It is happening now, it happened in the ancient days too. The earth was highly heated at the time of its creation. There was no wind, water nor any animal. It took millions of years of chemical reactions for the creation of atmosphere, water and thousands of other elements. These altogether contributed to the habitability of the earth for animals. All animals including human beings, microscopic lives like bacteria, amoeba, huge trees and animals have bodies which contain various kinds of chemicals. Each body is a kind of chemical factory where chemical reactions are taking place every moment. We live because of these chemical reactions. Again, with the advent of civilization, humans have produced various necessary items and products by means of chemical reactions and put them to their use. For example, the dresses you put on, the paste you brush your teeth with, the comb you fix your hair with, the cosmetics you use on your skin- all are chemical products. Besides, soap, toilet cleaner, life saving drugs, all are chemicals too. We use fertilizers and insecticides in our field crops, use petrol, diesel etc. in vehicles. These are industrial products made out of chemical reactions. In fact, the scope of Chemistry is so vast that it cannot be summarized easily." }, { "section": "Table 1.02: Some Scopes of Chemistry", "tables": [ { "headers": ["Substance", "Element", "Source and Chemical Change"], "rows": [ { "Substance": "Air", "Element": "Mostly nitrogen and oxygen", "Source and Chemical Change": "When we breathe in, the oxygen from the air enters our body, and reacts with the decomposed food inside to produce energy. In this process, food regulates the intensity of the reaction through the control of nitrogen." }, { "Substance": "Drinking water", "Element": "Water and mineral salts", "Source and Chemical Change": "Water plays a role in the chemical reactions that take place inside our body. It also works as solvent of various substances in the body. The poisonous substances in the body mix with water and come out in the form of urine and sweat. Mineral salts such as calcium, magnesium etc. play a vital role for our body. People may die if there is a lack of water in the body (dehydration). This is the main cause of death of people in cholera." }, { "Substance": "Fertilizer", "Element": "Nitrogen, phosphorous, calcium, magnesium, potassium etc.", "Source and Chemical Change": "Just as we eat food, plants also need food. The main components of plant food are nitrogen, phosphorus etc. Plants collect them from the soil. Different fertilizers contain compounds of these substances. As a result, these fertilizers act as nutrients and help get a good harvest." }, { "Substance": "Paper", "Element": "Cellulose", "Source and Chemical Change": "Paper is one of the most significant inventions of human civilization. Bamboo, the outer skin of sugarcane etc. contain huge amounts of cellulose. The paper mills turn these sources into paper by means of chemical reaction." } ] } ] }, { "section": "1.3 Relationship Between Chemistry and Other Branches of Science", "text": "There are various branches of science like chemistry, biology, physics, mathematics, environmental science, soil science etc. Each of these branches is related to the other branches. Very much like the other branches are related to chemistry, so is chemistry related to the other branches. Let us now check the relationship with some examples.\n\nRelationship with Biology: All plants produce glucose on their green parts in the photosynthesis process. Photosynthesis is basically a chemical process. Plants take in carbon-di-oxide from air with the help of their leaves and water from the soil with the help of their roots. Then it uses the chlorophyll of its green parts to produce glucose through the reaction between water and carbon dioxide. Animal bodies digest the carbohydrates or proteins of animal's intake and produce glucose, amino acid etc. All animal bodies are indeed stuffed with various chemicals. Biology discusses these chemicals and chemical reactions that take place inside the bodies of plants and animals. That is where the two sciences are interrelated.\n\nRelationship with Physics: Physics discusses magnet, electricity, different machines etc. Battery used for getting electricity is contribution of chemistry. Energy gleaned by burning oil, gas or coal is the source for vehicles and electricity. Chemistry is also dependent on physics. Physical chemistry is a branch of chemistry, the theories of which are essentially dependent on theories and formulas of physics. Nuclear Physics and nuclear chemistry are intertwined.\n\nRelationship with Mathematics: Mathematics has a close relationship with chemistry. In various fields of chemistry, especially in calculations, from simple to complex mathematical formulas are used. For example, determining the concentration of a solution, determining the composition of a compound, determining the rate of a reaction, etc.\n\nIn the same way, chemistry is directly and indirectly related to the other branches of science too." }, { "section": "1.4 The Importance of Studying Chemistry", "text": "Imagine what happens on a typical day with you. You use toothpaste, once you get up from bed in the morning. Then you start reading your books. Your mother serves you biscuits and tea. After finishing that, you take your bath. When you enter the washroom, you find it a bit unclean. You use toilet cleaner to clean it and then have bath using scented soap and shampoo. You use lotions after bath. Then you take your breakfast and go to school. The teacher there uses chalk on the board to simplify your lessons. Now, do you see, all the things you are using, e.g. paste, biscuit, tea, toilet cleaner, soap, shampoo, chalk etc. are contributions of chemistry.\n\nNot only that, we use fertilizers to increase fertility of fields, use insecticides to keep away insects from our crops, use preservatives to store the food for a longer time. This way, the whole process of food and cultivation is dependent on chemistry.\n\nToday, cholera, typhoid, tuberculosis etc. are curable diseases but they were once killer diseases. Thanks to chemistry, we have been relieved from the dreadfulness of recent corona. - How can you justify? Millions of people died of them in the ancient days. Humans have invented cures for them by means of their knowledge of chemistry. Nowadays, the field of medicine has developed so much that many people are cured of different cancers too.\n\nChemical wastes from industries, vehicles, consumer products etc. are doing harm to our environment. These contain carbon dioxide, carbon monoxide, sulphur dioxide, various acids, heavy metals like mercury, lead, arsenic, cobalt etc. When they come in contact with air, air is polluted, when they come in touch with water, water gets polluted. They enter human bodies and harm them. Again, use of excess chemicals is harmful for us. Insecticides help us save our crops but excess insecticide gets washed away to the water bodies, polluting the water. Some of it gets vaporized and pollute the air. By studying chemistry, you can explain all these natural and life oriented facts.\n\nBy now you should have understood that chemistry plays a significant role in our advancement but excess of it is harmful for us and nature as well. Many diseases are still there which do not have cures. Our duty is to study chemistry and try inventing those drugs. Therefore, learning chemistry does not only benefit us by means of newer inventions, it also helps us realize how we are harming our nature. By learning chemistry, you can take the world steps ahead. This is what we expect from you." }, { "section": "1.5 The Process of Research in Chemistry", "text": "The aim of science is the betterment of humanity. Scientists are constantly working with the same aim in their minds. The term scientist certainly rings the names of great scientists like Einstein, Newton, Archimedes, Lavoisier, Galileo etc. They are obviously great scientists. However, the meaning of the term scientist has the scope for you too to be called yourself a scientist. Indeed, science is that knowledge which is gleaned out of systematic experimentation. The process to glean knowledge by experimenting is known as research. One who carries out such research is a scientist.\n\nTherefore, if you carry out research, you can also be a scientist. Experimenting through a perfect and systematic process in order to learn something is called research. It means, there is a certain procedure to carry out a research. Research in chemistry also follows some procedure. Now we shall learn the steps of this procedure.\n\nIn the first step of a research, you need to determine what you want to learn or what new thing you want to invent. Suppose, you want to learn whether heat will be produced or absorbed as ammonium chloride is dissolved in water. This is known as topic selection.\n\nIn the second step, you have to investigate the matter. At this stage, you will read some books or some articles from the internet and other sources in order to learn how such kind of an experiment was carried out by someone else and what result it did yield. Suppose, you have learned that another chemical compound calcium oxide, when dissolved in water, produces heat. You will also be able to learn what kind of apparatus, chemicals and steps were followed in this experiment. That will give you an idea about what things you will require to conduct the test yourself. Besides, you will have an idea about the probable result- in this case, if you dissolve ammonium chloride in water, heat will be produced.\n\nAgain, you will be able to decide what kind of materials you are going to use and what will be the steps of the experiment. You came to know that you would need a beaker, water, ammonium chloride, thermometer, glass rod, balance etc. First you will take water in the beaker. You will record the temperature of the water in the beaker with the thermometer. Then, you will weigh ammonium chloride using the balance and mix and dissolve that with the glass rod in the water, a number of times. Each time, you need to check the temperature of water. This is the procedure of your experiment. Now you can start your experiment.", "tables": [ { "caption": "Table 1.03: Dissolving ammonium chloride in water", "headers": ["Quantity of dissolved ammonium chloride in water of beaker", "Temperature of the solution"], "rows": [ ["0g (nothing dissolved)", "25℃"], ["5g", "20℃"], ["10g", "15℃"], ["15g", "10℃"] ] } ], "figures": [ { "caption": "Steps in a research in Chemistry", "reference": "Fig 1.02" } ] }, { "section": "1.6 Safety Measures in Chemistry Laboratory and in use of Chemicals", "text": "The room or place where scientific experiments are carried out is called the laboratory. Similarly, the place where experiments of chemistry are carried out is called Chemistry laboratory. It is understood, there will be various chemicals in a chemistry laboratory. Almost all chemicals are harmful to some extent for us as well as our environment. Some chemicals are prone to explosion, some are flammable, some harm our body directly and some are dangerous for nature. Most of the apparatus in a chemistry laboratory are made of glass. Therefore, we need to be cautious from the moment of entry into the laboratory to the moment we come out. Lack of caution may result in accidents, e.g. if acid falls on your body, you will get injured; if acid falls on your dress, the dress will be spoiled. Besides, there may be accidents including fire or explosion in a laboratory. Therefore, you need to wear an apron. The apron will be knee- long and the sleeves will be up to your wrist. Its colour will be white. You will use hand gloves and safety goggles on your eyes. Some of these safety measures are given in the following picture:\n\nBelow are some pictures of things that need to be used in the chemistry laboratory for self- protection.", "figures": [ { "caption": "Apron, goggles, hand gloves and musk", "reference": "Fig 1.03" } ] }, { "section": "Table 1.04: Signs and their Explanations Identifying Risk", "tables": [ { "headers": ["Sign", "Risk, Extent of risk and precaution"], "rows": [ { "Sign": "Explosive substance", "Risk, Extent of risk and precaution": "We need to be very careful about these substances. We must keep in mind that friction and fire in these substances may cause serious explosion which will be harmful for our body as well as the laboratory. We need extreme caution in handling these. TNT, organic peroxide, nitroglycerine etc. are such kind of substances." }, { "Sign": "Flammable substance", "Risk, Extent of risk and precaution": "Alcohol, ether etc. are flammable substances. These may catch fire quickly. Therefore, we need to keep them away from fire or heat." }, { "Sign": "Toxic substance", "Risk, Extent of risk and precaution": "Substances with this sign are poisonous. If we come in touch with them or inhale them, they may cause harm to our body. Benzene, chlorobenzene, methanol, etc. are such substances. We must wear apron, hand gloves, safety goggles and musks when handling them." }, { "Sign": "Irritant substance", "Risk, Extent of risk and precaution": "Cement dust, light acids, base, nitrous oxide etc. cause irritation on skin, eyes and breathing system. We must wear aprons, hand gloves, safety goggles and musks when handling them." }, { "Sign": "Hazardous substance", "Risk, Extent of risk and precaution": "Direct contact on skin or inhalation of such substances may cause short or long term harm to our health. They may affect our breathing system or even cause diseases like cancer. Benzene, toluene, xylene are such substances. We must wear aprons, hand gloves, safety goggles and musks when handling them." }, { "Sign": "Radioactive substance", "Risk, Extent of risk and precaution": "These substances emit harmful rays which may cause diseases like cancer or disable somebody. We need to be extremely cautious in handling these. Uranium, radium etc. are of this kind." }, { "Sign": "Dangerous for environment", "Risk, Extent of risk and precaution": "Substances with this sign are dangerous for the environment. Lead and murcury are examples of such substances. They require caution when in use. Again, they have to be gathered in a place after use. They have to be recycled as much as possible. That way, they cannot do much harm to the environment." }, { "Sign": "Corrosive", "Risk, Extent of risk and precaution": "These cause injury to body in contact. Inhalation of such substances may cause injury inside the body. Hydrochloric acid, sulfuric acid and concentrated sodium hydro-oxide etc. are examples of this kind." } ] } ] } ] }, { "chapter_number": 2, "title": "States of Matter", "start_page": 17, "end_page": 34, "content": [ { "section": "2.1 States of Matter", "text": "Anything that has a certain mass and occupies space is a matter. At normal room temperature some matters may exist as solids, some as liquids and some as gasses. For example, at normal room temperature sugar, edible salt, marble etc. exist as solids; water, oil, kerosene etc. exist as liquids and nitrogen, oxygen, carbon dioxide etc. exist as gasses. Again, changing the temperature, the same matter's state can be transformed into any of solid, liquid or gaseous states. A short discussion on the properties and characteristics of solids, liquids and gaseous matters is given below.", "subsections": [ { "title": "2.1.1 Solids", "text": "A solid matter has a specific mass, shape, and volume. Molecules of all matters have a force of attraction. It is known as inter molecular attraction. This force is the most in the solid matters. As a result, the molecules or particles in solids stay very close to each other in a fixed state and they take a fixed dimension which cannot be compressed with pressure. Again, a solid matter hardly changes shape when the temperature is raised. Particles of solids can not move or leave space, but can vibrate in their own place." }, { "title": "2.1.2 Liquids", "text": "Liquids have a specific mass and volume but do not have a shape. Liquids take the shapes of their containers. Since the molecules of a liquid remain farther from each other than those of solids, the inter molecular force of attraction is also less than solids. Such matters do not decrease volume when force is projected on them but the volume increases with the rise of temperature. This change of volume is greater than that of solids." }, { "title": "2.1.3 Gases", "text": "Gases have specific mass but they do not have specific volume or shape. Whatever quantity of gas is put into any size of container, it takes over the full size of that container. The molecules in gases stay too far away than those of liquids or solids. The inter molecular force of attraction is also very low among them. A small quantity of pressure is enough to compress gases and in the same way, a small amount of temperature is enough to increase the volume of such matters." } ] }, { "section": "2.2 Kinetic Theory of Particles", "text": "Every substance is made of small particles which remain together by means of an inter molecular force of attraction. These molecules also have a kinetic force in them. The attempt to prove the states of substances using inter molecular force of attraction and the kinetic force of the particles is known as the kinetic theory of particles. When the particles inside a substance remain in very high force of attraction, they stay together and cannot move. This is the solid state. When heat is applied on such a solid substance, the particles start to vibrate.\n\nWhen more heat is applied, the particles lose some of their force of attraction and they get some movement. This state of matter is called a liquid. Liquid takes the shape of the container without changing their volume. When more heat is applied on this liquid state of the substance, the particles receive the heat and the kinetic force in them is increased. This kinetic force is increased to a level where they lose inter molecular force of attraction almost completely and start to move freely. This is the gaseous state. That is why gaseous matter has no absolute volume. The volume of the container in which it is kept is the volume of the gas. When more heat is applied to this state of the substance, the particles will increase their speed of movement.", "figures": [ { "caption": "Kinetic theory of particles", "reference": "Fig 2.01" } ] }, { "section": "2.3 Diffusion", "text": "The movement of particles of a substance in solid, liquid and gaseous media to spread spontaneously and uniformly is called diffusion. In diffusion process, solid, liquid or gas moves spontaneously from a place of higher concentration to lower concentration. Remember, what happens if you leave a perfume bottle with its lid open in the corner of a room? Within some time, you will find the whole room smelling of perfume. This is an instance of diffusion. The medium in which the particles take less time to diffuse has a higher diffusion rate, and the medium in which the particles take more time to diffuse has a lower diffusion rate. For example, the rate of diffusion in a gaseous medium is higher than in a liquid medium. Similarly, the rate of diffusion in a liquid medium is higher than in a solid medium. Again, in the same medium, the rate of diffusion of particles of a substance whose molecular mass is higher will be lower.", "experiments": [ { "title": "Experiment 1", "description": "At room temperature, take some pure water in a glass jar. Add a small quantity of solid pink potassium permanganate (KMnO4) into it. You will see, after sometime, the KMnO4 grains are dissolving into a pink solution. Indeed, the KMnO4 particles are getting motion and scattering freely in the water. In this case, some solid matter is diffused in water or liquid. This spread can take from a few minutes to about an hour. However, if heat is applied, the rate will increase.\n\nSimilarly, if we do the experiment of diffusion of potassium permanganate in hot water, the water will turn into pink solution faster. In this case, the KMnO4 particles will get added motion due to heat and scatter faster. This shows that the presence of heat increases the rate of diffusion of solids.", "figures": [ { "caption": "KMnO4 solution in water", "reference": "Fig 2.02" } ] }, { "title": "Experiment 2", "description": "At room temperature, take some pure water in a beaker and add some liquid blue in it. Within a few moments, you will see that the water has turned blue. That means, the particles of blue solution or some liquid have diffused in the water. The temperature being the same, it has taken the liquid less time to diffuse in another liquid than solid KMnO4. That means, the rate of diffusion of liquid matter in another liquid is faster than in solid matter. The presence of heat will increase the rate. Just like solids and liquids, diffusion of gases takes place in the liquid medium. However, at a given temperature, the diffusion rate of gaseous substances is higher than that of solids and liquids in liquid mediums.", "figures": [ { "caption": "Diffusion of liquid solution in liquid", "reference": "Fig 2.03" } ] }, { "title": "Experiment 3: Diffusion of two gases", "description": "Take a glass tube with both faces open. Take two pieces of cottons. Soak a piece of cotton in concentrated hydrochloric acid (HCl) solution and soak the other in ammonium hydroxide (NH4OH) solution. Now close the glass tube fixing each of the cottons to a side of it. Here hydrogen chloride gas from HCl solution and ammonia gas from NH4OH solution will get diffuse through the air inside the tube. Air is a gaseous medium.\n\nWithin a few moments, you will see a white smoke filling up the tube. It is ammonium chloride (NH4Cl), produced in the reaction between hydrogen chloride gas and ammonia gas. It takes less than a minute to produce white smoke. The white smoke will not be positioned in the centre of the tube; it will be nearer to the hydrochloric acid solution. That means at a same given time, hydrogen chloride gas has gone a lesser distance than ammonia. That also proves that ammonia gas spreads faster than hydrogen chloride gas because of its faster rate of diffusion. The reason behind it is the difference in their atomic masses. A gas with lesser atomic mass will have a better diffusion rate. Here atomic mass (17) of ammonia gas is lesser than the atomic mass (36.5) of hydrogen chloride. As a result, ammonia (NH3) gas has diffused and spread faster than hydrogen chloride (HCl) gas.\n\nAtomic mass of H2, He, N2, O2 and CO2 gases are 2, 4, 28, 32 and 44 respectively. Since hydrogen is the gas with the least atomic mass, its rate of diffusion is faster than others while carbon dioxide's being the most, is the slowest. We have seen that the rate of diffusion of substances through gaseous media is higher than through liquid media, which can be 50 to 100 times.", "figures": [ { "caption": "Diffusion of two gases", "reference": "Fig 2.04" } ] } ] }, { "section": "2.4 Effusion", "text": "Effusion is a process by which gas particles are expelled one by one through a very small opening without colliding with each other, such as gas escaping through a small hole in a balloon. If a balloon has tiny or microscopic holes, it will gradually deflate and lose air over time. This happens because the gas particles escape through the tiny holes one by one. This slow release of gas is called effusion.\n\nAlso, if a tire has a very small hole, the gas slowly escapes through that hole in the form of particles. It is not like a loud explosion or a sudden explosion. This kind of slow and gradual release is called effusion.", "subsections": [ { "title": "Practical Uses of Effusion", "text": "Leak detection in gas cylinders and pipelines: Leakage occurs when gas is slowly released through small holes in a gas cylinder or pipeline. This slow release of gas can be monitored to identify leaks or defects. The valve and line of LPG cylinder leakage can be checked regularly with soapy water. For example, a gas cylinder or pipeline is covered with soapy water. If something like small bubbles are seen, it means that there are small holes in the cylinder or pipeline through which effusion is occurring.\n\nDetermining the molar mass of a gas: Researchers determine the effusion rate of two unknown gases by comparing their molar masses. The lighter gas escapes faster, the heavier gas slower, and this is how they determine how heavy a gas is." } ] }, { "section": "2.5 Burning of a Candle and the Three States of Wax", "text": "Wax is a mixture of various hydrocarbons. Organic compounds made of hydrogen and carbon are known as hydrocarbons. In the burning of a wax, three states of matter can be observed simultaneously. There is a thin thread or wicks inside the wax. When we add fire to it, the hydrocarbon particles around the thread or wicks melt into liquid. The liquid wax absorbs heat and vaporizes first. Then the vaporized wax starts a reaction with oxygen of the air and produces carbon dioxide, water vapor, light and heat. A portion of the liquid wax remains and turns solid again. Thus, in the presence of heat we see three states of wax.", "figures": [ { "caption": "Burning of wax", "reference": "Fig 2.05" } ] }, { "section": "2.6 Melting and Boiling", "text": "The process of transforming a solid matter into liquid by means of applying heat is called melting. At normal pressure (1 atmospheric pressure), the temperature at which a solid matter turns into liquid state is called the melting point of that solid. Each pure solid matter has its own melting point, like the melting point of ice is 0°C.\n\nThe process of transforming a liquid matter into gas by means of heat is called boiling. At normal pressure (1 atmospheric pressure), the temperature at which a liquid matter turns into gaseous state is called the boiling point of that liquid. Each pure liquid matter has its own boiling point, like the boiling point of water is 100°C. The boiling process requires heat but solidification requires removal of heat.", "experiments": [ { "title": "Experiment 4", "description": "Suppose, we want to find out the melting point of urea, a solid matter. First, we need to put a net on a tripod, upon which we shall place a watch glass. Now we shall put some urea on the watch glass. Fix a thermometer with a liner on a stand and put the bulb of thermometer in the urea. Now start giving heat to the urea. You will find, the urea will start to melt at 133°C temperature and all the fertilizer will melt at the same temperature. This 133°C is the melting point of urea. Again, let's find out the melting point of an impure matter, wax. In order to find it out, first we need to turn the wax into powder. Collect the wax powder inside a glass tube with one side closed. Now fix a thermometer inside following the fig 2.07. Sink the glass tube in the beaker in such a way so that water can't get inside the tube. Now, start heating the beaker slowly. You will find the wax melting at a specific range of temperature instead of a fixed temperature. This range of temperature is the melting point of wax.\n\nMelting point of impure substances is lesser than that of pure substances. It is opposite in the case with boiling point. A mixed matter will have no fixed melting and boiling point. Since all pure solids have a specific melting point, they melt at that temperature. If a solid substance melts at any other temperature, the solid can be declared impure. Again, if it melts over a range of temperatures, it is impure too. For example: the melting point of sulfur at 1 atm is 115°C. But in an experiment, if sulfur melts at any other temperature or range of temperatures, the sample of sulfur can be declared adulterated. Therefore, finding the melting point can be a way to find the purity of solid substances.", "figures": [ { "caption": "Melting point of urea", "reference": "Fig 2.06" }, { "caption": "Melting point of wax", "reference": "Fig 2.07" } ] }, { "title": "Experiment 5: Boiling Point of Liquids", "description": "Some sample of the liquid (Example: water), the boiling point of which needs be determined, is taken in a beaker. The beaker is fixed with a thermometer. Now, the beaker will be heated carefully with a Bunsen burner. At a certain temperature, the water in the beaker will turn into vapor. That temperature is the boiling point of water. All the water in the beaker will vaporize at 100°C.\n\nThat sets the boiling point of water at 100°C (at 1 atm). Since each liquid matter has a specific boiling point, so a boiling point cannot be the same for two liquids. Again, if a liquid is adulterated, it will boil at a different temperature. For example, if we add some alcohol to water, it will boil at a different temperature than 100°C. So, boiling point can be a determiner of the purity of a liquid.", "figures": [ { "caption": "Boiling point of water", "reference": "Fig 2.08" } ] }, { "title": "Experiment 6", "description": "Let us take some ice cubes in a beaker and heat it carefully. We shall keep watch on an attached thermometer throughout the process. Let's assume, the initial temperature of the ice was -40°C.\n\nWhen the temperature of the ice reaches 0°C absorbing the heat, they melt into liquid. The temperature remains stagnant at 0°C until all the ice cubes melt into the water. That proves 0°C as the melting point of ice. The straight line in the temperature is called the melting point line. In the fig 2.09, line AB is the melting point line. Both ice and water exist through the length of the line. If we apply more heat, the temperature of water starts to rise. When it reaches 100°C, you'll see more heat will not be able to raise the temperature of water anymore. Rather, the water transforms into vapor. All the water will vaporize at this 100°C temperature. If we apply more heat after that, the temperature of the water vapor will increase. The boiling point of water is 100°C. CD is the line of boiling point. Water and vapor co-exist at this line.\n\nAgain, collect the data of cooling the water vapor and set them on a graph sheet with X axis telling time and Y axis telling temperature. It will be like fig 2.10.\n\nThe graph shows the initial temperature of water vapor is 140°C. When in the process of cooling it to 100°C, the vapor starts to turn into water. It remains 100°C until all the vapor is turned into water. Further cooling starts to decrease the temperature of water. When it reaches 0°C, the water starts to transform into ice. It remains the same until all the water is turned into ice and then the temperature of ice decreases from 0°C. The fig 2.10 shows a decrease of temperature of ice to -40°C.", "figures": [ { "caption": "Graph of applying heat on ice", "reference": "Fig 2.09" }, { "caption": "Cooling curve of vapor", "reference": "Fig 2.10" } ] } ] }, { "section": "2.7 Distillation and Sublimation", "text": "The process of heating a liquid and turning it into gas is called evaporation or vaporization. When a pot of tea is heated, water from the hot tea is converted to vapors, that is an example of vaporization. Again if we cool that vapor, the vapor turns into liquid. This process is called condensation. For example, water vapor emits heat and turns into water, which is condensation. The process of heating a liquid into vapor and then retrieving the liquid from the vapor by cooling it is called distillation. That means distillation is a combination of the processes of vaporization and condensation.\n\nDistillation = vaporization + condensation\n\nFigure 2.11 shows the change of state of a volatile substance by applying heat.\n\nThe process in which heating a solid directly turns that solid into a gaseous substance instead of a liquid, is called sublimation. Ammonium Chloride (NH4Cl), camphor (C10H16O), Naphthalene (C10H8), solid Carbon dioxide (CO2), Iodine (I2), Aluminium Chloride (AlCl3) etc. are matters that do not turn liquid if heat is applied. Instead, they turn into vapor. These substances are called sublimated substances.", "experiments": [ { "title": "Experiment 7", "description": "Take some solid aluminium chloride salt in a beaker. Put a glass lid on its open face. Put some ice cubes on the lid. Now, apply heat slowly on the beaker. You'll see the solid AlCl3 is turning into gaseous form absorbing heat. This gaseous AlCl3 again reaches the lid and under the influence of ice, condenses itself underneath the lid.", "figures": [ { "caption": "Sublimation of AlCl3", "reference": "Fig 2.12" } ] } ], "subsections": [ { "title": "Application of sublimation", "text": "If a sublimated substance is mixed with some solid matter, it can be retrieved by means of the sublimation process. For example, if some ammonium chloride (NH4Cl) is mixed with some edible salt (NaCl), it (NH4Cl) can be separated by the process of sublimation. If heat is continuously applied to a sublimated substance, it vaporizes. In iodized salt, iodine is a sublimated substance. If you apply heat to that salt, the iodine will be vaporized from there.\n\nThe vapor can be cooled into solid iodine. However, since the mixture of sand and glucose does not contain any sublimated substance, therefore, you cannot separate them by sublimation." } ] } ] }, { "chapter_number": 3, "title": "Structure of Matter", "start_page": 35, "end_page": 58, "content": [ { "section": "3.1 Elements and Compounds", "text": "Certainly you have seen gold, silver or iron. No matter how far you break pure gold, you will get nothing but gold. The same is applicable in the cases with silver or iron. When divided, the matter which does not yield anything but itself, is called element. Besides the above three, nitrogen, oxygen, phosphorus, carbon, helium, argon, calcium, magnesium, sulfur etc. are also elements. So far, a total of 118 elements have been discovered. Out of them, 98 elements are available in nature and the rest are made in the laboratory. The second group is known as synthetic elements. Do you know that your body contains as many as 26 different elements?", "subsections": [ { "title": "Compounds", "text": "You have already known that an element yields the element only. If water is analyzed, we shall find two different elements- hydrogen and oxygen. The same way, if we analyze a writing chalk, we get calcium, carbon and oxygen. The substances which, if divided, give away two or more elements are called compounds. In a compound, elements will always exist in the same ratio. For example, chemical analysis of any water sample collected from any place will show two hydrogens and one oxygen. That means, the ratio of hydrogen and oxygen atoms in water is 2:1. The characteristics of compounds are different from those of elements they are made of. Again, for example, at normal room temperature, hydrogen and oxygen are gaseous elements but when they make water, it is a liquid." } ] }, { "section": "3.2 Atoms and Molecules", "text": "Atoms are the smallest particles of elements that contain the characteristics of the elements. For example: Nitrogen atoms contain the characteristic features of nitrogen while oxygen atoms contain the features of oxygen.\n\nWhen two or more atoms remain connected with each other in a chemical bond, it is known as a molecule. You will learn about chemical bonds in detail in chapter five. Two oxygen atoms (O) bond to each other to form an oxygen molecule (O2). Again, a carbon atom (C) bonds with two oxygen atoms (O) to generate a carbon dioxide (CO2) molecule. When more than one atoms of a specific element bond each other, they produce that element's molecule, like O2. When atoms of different elements bond together to produce a molecule, it is called a molecule of the compound, like CO2." }, { "section": "3.3 Symbols of Elements", "text": "The abbreviated form of English or Latin name of an element is called its symbol. Each element has its own symbol. There is a system of writing a symbol of an element.", "tables": [ { "caption": "Table 3.01: Symbols of Elements", "headers": ["Element", "Symbol"], "rows": [ ["Hydrogen", "H"], ["Oxygen", "O"], ["Nitrogen", "N"] ] }, { "caption": "Table 3.02: Symbols of Elements (First letter same)", "headers": ["Element", "Symbol", "Element", "Symbol"], "rows": [ ["Carbon", "C", "Cobalt", "Co"], ["Chlorine", "Cl", "Cadmium", "Cd"], ["Calcium", "Ca", "Chromium", "Cr"] ] }, { "caption": "Table 3.03: Symbols of Elements (Latin Name)", "headers": ["Element", "Latin Name", "Symbol"], "rows": [ ["Sodium", "Natrium", "Na"], ["Copper", "Cuprum", "Cu"], ["Potassium", "Kalium", "K"], ["Silver", "Argentum", "Ag"], ["Tin", "Stannum", "Sn"], ["Antimony", "Stibium", "Sb"], ["Gold", "Aurum", "Au"], ["Lead", "Plumbum", "Pb"], ["Tungsten", "Wolfram", "W"], ["Iron", "Ferrum", "Fe"], ["Mercury", "Hydrurgyrum", "Hg"] ] } ] }, { "section": "3.4 Formula", "text": "One Hydrogen molecule is expressed as H2. It means, there are two Hydrogen atoms in that molecule. Again, one molecule of water is expressed as H2O, meaning, it contains two Hydrogen atoms and one Oxygen atom.", "tables": [ { "caption": "Table 3.04: Formula of Molecules", "headers": ["Name of Molecule", "Formula"], "rows": [ ["Nitrogen", "N2"], ["Ammonia", "NH3"], ["Chlorine", "Cl2"], ["Sulfuric Acid", "H2SO4"], ["Hydrochloric Acid", "HCl"] ] } ] }, { "section": "3.5 The Fundamental Particles of an Atom", "text": "Each atom consists of three stable particles- electrons, protons and neutrons. These particles are called fundamental particles of atoms. Protons and neutrons remain in the nucleus or at the center of the atom while electrons continue to move around the nucleus.\n\nElectron: Electron is one of the fundamental particles of atom containing negative charge. The amount of this charge is -1.60×10^-19 coulombs. It is expressed through the symbol e. An electron has the mass of 9.11×10^-28 g. The relative charge of electron is taken to be -1 and the mass of electron is 1840 times less than the mass of proton and neutron. That is why, the relative mass of electron is taken as 0.\n\nProton: Proton is one of the stable particles of an atom containing positive charge. The charge is +1.60×10^-19 coulomb. It is expressed by p. The mass of proton is 1.67×10^-24 g. The relative charge of proton is taken as +1 and relative mass is taken as 1.", "tables": [ { "caption": "Table 3.05: Fundamental Particles", "headers": ["Name of Particle", "Symbol", "Actual Charge", "Actual Mass", "Relative Charge", "Relative Mass"], "rows": [ ["Electron", "e", "-1.60 × 10−19 coulomb", "9.110 × 10−28 g", "-1", "0"], ["Proton", "p", "+1.60 × 10−19 coulomb", "1.673 × 10−24 g", "+1", "1"], ["Neutron", "n", "0", "1.675 × 10−24 g", "0", "1"] ] } ], "subsections": [ { "title": "3.5.1 Atomic Number", "text": "Atomic number of an element is determined by the number of protons present in the nucleus of that element's atom. For example: an atom of Helium (He) has two protons in its nucleus, so the atomic number of Helium is 2. Again, an Oxygen atom has eight protons in its nucleus, so the atomic number of Oxygen is 8. The atomic number denotes an atom. Therefore, the atomic number can also be called the ID number of an element. If the atomic number is 1, we understand it is Hydrogen, if the atomic number is 2, we understand it is Helium, if the atomic number is 9, we understand it is Fluorine. Thus, atomic number is the permanent identity of an atom. Proton number or atomic number is expressed by Z. Since all atoms are charge neutral, so they contain the same number of electrons as is the number of protons in its nucleus." }, { "title": "3.5.2 Mass Number", "text": "The mass number of an atom is denoted by the total number of protons and neutrons in its nucleus. The mass number is expressed by A. Since the mass number is the summation of neutrons and protons, we can get the number of neutrons in an atom by deducing its proton number from the mass number. The mass number of Sodium (Na) is 23, its proton number is 11; so the number of neutrons in sodium is (23 - 11) = 12.\n\nThe atomic number of an atom is written at the lower left corner of its symbol while its mass number is written at the upper left corner. In the case with Sodium (Na), where atom number is 11 and mass number is 23. It will be written as 23^11Na.", "tables": [ { "caption": "Table 3.06: Short Form of Different Elements", "headers": ["Symbol", "Atomic/Proton Number (z)", "Mass Number A", "Number of Electrons", "Number of Neutrons (A-Z)", "Short Form"], "rows": [ ["H", "1", "1", "1", "0", "1^1H"], ["He", "2", "4", "2", "2", "4^2He"] ] } ] } ] }, { "section": "3.6 Atomic Model", "subsections": [ { "title": "3.6.1 Rutherford's Atomic Model", "text": "Rutherford has given a model on the structure of atom in 1911. The model states:\n\na. In the centre of an atom there is a positively charged dense central core. This core is called the nucleus of the atom. Protons and electrons are situated inside this nucleus while only electrons are found outside the nucleus. Since, compared to the whole mass of the atom, the mass of electron is zero, so protons and neutrons inside the nucleus determines the whole mass and positive charges of the atom.\n\nb. The nucleus is very small and most of the space outside the nucleus and inside an atom is void.\n\nc. Electrons in an atom always move round the nucleus in different orbits like the planets revolve round the sun in the solar system. The number of electrons in an atom is same as the number of protons. Since the charge of an electron and proton in an atom are equal and opposite, therefore the overall charge of an atom is zero.\n\nd. The electrons with negative charge are attracted to the positively charged nucleus. The force of this attraction is centripetal and due to this centripetal force, electrons move round the nucleus like our earth does around the sun.\n\nRutherford's model is compared to the solar system model for its continuous parallelism to the solar system. Again, since the Rutherford model first gave the idea of a nucleus, it is also called the nuclear model.", "figures": [ { "caption": "Rutherford's atomic model", "reference": "Fig 3.01" } ] }, { "title": "Limitations of Rutherford's Model", "text": "Rutherford is the first scientist to introduce the idea of a nucleus and orbits of an electron. Although his model is the first acceptable atomic model, it has some limitations. They are:\n\na. Rutherford's model did not give any idea about the size (radius) and shape of the orbits along which the electrons move.\n\nb. Planets including the sun in the solar system are electrically neutral but electrons and nucleus are charged. A parallelism between some charge neutral elements such as our planets and charged elements such as nucleus and electrons is not quite correct.\n\nc. There is no satisfactory explanation regarding how the electron will move round the nucleus in the case of atoms having more than one electron.\n\nd. According to Maxwell's electromagnetic theory of radiation, any charged particle moving in a circular path, always loses energy and its radius will gradually grow smaller. At a stage, it falls into the nucleus. That means there will be the end of the atom or at least its stability will be in trouble. However, that does not happen in nature; in other words, according to Maxwell's theory, Rutherford's atomic model is not correct.", "figures": [ { "caption": "Electron falling on nucleus", "reference": "Fig 3.02" } ] }, { "title": "3.6.2 Bohr's Atomic Model", "text": "Scientist Neils Bohr gave some corrections to Rutherford's atomic model in 1913. This corrected model is called the Bohr's atomic model. The main postulates of this model are:\n\na. The electron moves around the nucleus in a circular motion in a specific radius, about an axis. This circular motion is called an energy level or orbit. They are also known as shell or permanent orbit or principal energy level. Electrons do not absorb or emit any energy when they revolve round these fixed orbits. If we express the permanent orbit as n, then n = 1,2,3,4 etc. In other words, if n = 1, the principal energy level is K, when n = 2, L is the principal energy level, when n = 3, M is the principal energy level, when n = 4, N is the principal energy level etc.\n\nb. According to Bohr's model, the angular momentum of an electron in an energy level is mvr = nh/2π. Here,\n\nm = the mass of electron (9.11×10^-31 kg)\nr = the radius of the orbit that the electron revolves round\nv = the velocity of electron in the permanent orbit\nh = Planck constant (h = 6.626×10^-34 m^2 kg / s)\nn = principal energy level or principal quantum number (n = 1,2,3,4, ...)\n\nAccording to this, the energy level with a lesser value of n is the lower energy level and the energy level with a higher value of n is the higher energy level.\n\nWhen an electron moves a round in its principal energy level, it does not absorb or emit any energy. However, it absorbs energy when it moves from a lower to a higher energy level. The same way, an electron emits energy when it moves from a higher to a lower energy level. This absorbed or emitted energy is hv = hc/λ. Here,\n\nc = velocity of light (3×10^8 ms^-1)\nv = frequency of absorbed or emitted energy (unit s^-1 or Hz)\nλ = length of energy wave absorbed or emitted (unit m)\n\nThe light emitted when an electron moves from higher energy level to lower energy level creates an atomic spectra when it goes through a prism.", "figures": [ { "caption": "Bohr's atomic model", "reference": "Fig 3.03" } ] }, { "title": "Success of Bohr's Model", "text": "a. Rutherford compared the orbits of electrons around nucleus to that of the planets in the solar system. It did not mention anything about the size of the energy levels, but Bohr's atomic model specifies the circular size of the energy levels.\n\nb. Rutherford's model does not mention about the changes in structure of atom when they absorb or emit energy. The Bohr model states that the electron moves from lower to upper energy level when the atom absorbs energy and it moves from upper to lower energy level when the atom emits energy.\n\nc. The Rutherford model does not explain the atomic spectra of an element but the Bohr model can explain the atomic spectra of hydrogen (H) atom with one electron." }, { "title": "Limitations of Bohr's Model", "text": "a. Although the Bohr model can explain the atomic spectrum of hydrogen containing one electron, it cannot explain the spectrum of ions or atoms containing more than one electron.\n\nb. When electrons are transferred from one energy level to another, according to Bohr, there will be a single line in the spectrum. But if we use high resolution apparatus, we can see every line consists of several fine lines. Why each line is the summation of various lines is not explained.\n\nc. The Bohr model specifies that orbits of electrons in an atom is circular. However, later on, it was proved that the orbits can be of oval shape too." } ] }, { "section": "3.7 Orbital Electronic Configuration of Atoms", "text": "The Bohr model states about the principal energy level. Each principal energy level can contain 2n^2 electrons at the highest, where n = 1,2,3 etc. According to this formula:\n\nFor energy level K, n = 1, so, the highest number of electrons in K is 2n^2 = (2×1^2) = 2.\n\nFor energy level L, n = 2, so, the highest number of electrons in L is 2n^2 = (2×2^2) = 8.\n\nFor energy level M, n = 3, so, the highest number of electrons in M is 2n^2 = (2×3^2) = 18.\n\nFor energy level N, n = 4, so, the highest number of electrons in N is 2n^2 = (2×4^2) = 32.", "tables": [ { "caption": "Table 3.07: Electronic Configuration of Elements [H(1)-Zn(30)]", "headers": ["Atomic Number", "Element", "K", "L", "M", "N"], "rows": [ ["1", "H", "1", "", "", ""], ["2", "He", "2", "", "", ""], ["3", "Li", "2", "1", "", ""], ["4", "Be", "2", "2", "", ""], ["5", "B", "2", "3", "", ""], ["6", "C", "2", "4", "", ""], ["7", "N", "2", "5", "", ""], ["8", "O", "2", "6", "", ""], ["9", "F", "2", "7", "", ""], ["10", "Ne", "2", "8", "", ""], ["11", "Na", "2", "8", "1", ""], ["12", "Mg", "2", "8", "2", ""], ["13", "Al", "2", "8", "3", ""], ["14", "Si", "2", "8", "4", ""], ["15", "P", "2", "8", "5", ""], ["16", "S", "2", "8", "6", ""], ["17", "Cl", "2", "8", "7", ""], ["18", "Ar", "2", "8", "8", ""], ["19", "K", "2", "8", "8", "1"], ["20", "Ca", "2", "8", "8", "2"], ["21", "Sc", "2", "8", "9", "2"], ["22", "Ti", "2", "8", "10", "2"], ["23", "V", "2", "8", "11", "2"], ["24", "Cr", "2", "8", "13", "1"], ["25", "Mn", "2", "8", "13", "2"], ["26", "Fe", "2", "8", "14", "2"], ["27", "Co", "2", "8", "15", "2"], ["28", "Ni", "2", "8", "16", "2"], ["29", "Cu", "2", "8", "18", "1"], ["30", "Zn", "2", "8", "18", "2"] ] } ], "subsections": [ { "title": "3.7.1 Concept of Energy Sublevel", "text": "We have seen all energy levels are specified with n. These levels are again divided into sublevels which are expressed by l. The value of l is from 0 to n-1. These sublevels are called orbitals. They are identified with s, p, d, f etc.. The value of l for different orbitals is shown below:\n\nWhen n = 1 l = 0. There will be one orbital: 1s.\nWhen n = 2 l = 0, 1. There will be two orbitals: 2s, 2p.\nWhen n = 3 l = 0, 1, 2. There will be three orbitals: 3s, 3p, 3d.\nWhen n = 4 l = 0, 1, 2, 3. There will be four orbitals: 4s, 4p, 4d, 4f.\n\nWhen n = 5 l = 0, 1, 2, 3, 4. There should be five orbitals. However, since all the electrons can be configured in the 4s, 4p, 4d, 4f orbitals, then there will not be any necessity for the fifth. The same is the case with n = 6, 7 and 8.\n\nThe number of subshells in each principal energy level is (2l + 1). We already know each principal energy level has 2n^2 number of electrons.\n\nNow in the following table we shall see that the summation of all orbitals turn into this 2n^2:", "tables": [ { "caption": "Table 3.08: Electronic Configuration in Energy Levels (n = 1 - 4)", "headers": ["Energy Level n", "Value of sublevel l according to n", "Orbital Name according to l", "Orbital Symbol", "Total Number of Electrons in Orbital 2(2l+1)", "Total Number of Electrons in Energy Level 2n²"], "rows": [ ["1", "0", "s", "1s", "2", "2"], ["2", "0", "s", "2s", "2", "2 + 6 = 8"], ["2", "1", "p", "2p", "6", ""], ["3", "0", "s", "3s", "2", "2 + 6 + 10 = 18"], ["3", "1", "p", "3p", "6", ""], ["3", "2", "d", "3d", "10", ""], ["4", "0", "s", "4s", "2", "2 + 6 + 10 + 14 = 32"], ["4", "1", "p", "4p", "6", ""], ["4", "2", "d", "4d", "10", ""], ["4", "3", "f", "4f", "14", ""] ] } ] }, { "title": "3.7.2 The Principles of Electronic Configuration in Atoms", "text": "There are three principles for electronic configuration in atoms: (1) Pauli's Exclusion Principle, (2) Aufbau Principle, and (3) Hund's Rule. You will find a detailed discussion of these principles in the higher secondary chemistry textbook. Here, we have provided a brief overview of these principles to explain electronic configuration in an atom.\n\nHere the basic concepts of these principles and the electronic configuration of atoms are briefly discussed. Electron first enters the lowest energy orbital of an atom and then gradually goes into the highest energy orbital. That means, the electron will enter the lowest energy level orbital first and then the highest energy level orbital. The energy level of the orbital is determined by the summation of value of principal energy level (n) and value of energy sublevel (l). The orbital that has a lesser value of (n + l) is of lesser energy level and at first an electron will enter this orbital. The orbital that has a higher value of (n + l) is of higher energy level and it gets the later entry of an electron.\n\nFor 3d orbital, n = 3 and l = 2, so the value (n + l) becomes (3 + 2 = 5). Again, for 4s orbital, n = 4 and l = 0, so the value (n + l) becomes (4 + 0 = 4). It shows 4s orbital has lower energy than 3d orbital. Therefore, the electron will first enter 4s orbital and then will go to 3d. Again, if the value (n + l) of two orbitals are equal, then the orbital with lesser value of n has lower energy and the electron will enter here first. In the same way, the orbital with higher n gets the electron later for being higher in energy.\n\nFor example, the values (n + l) of 3d and 4p are 3 + 2 = 5 and 4 + 1 = 5 respectively. Here in this case, since the value of n in orbital 3d is lesser than orbital 4p, so it is lower in energy and the electron will enter here first. Contrarily, since the value of n in 4p orbital is higher, its energy is higher than 3d orbital will get electrons later. According to this system, the gradual sequence of energy of orbital in receiving electrons will be:\n\n1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s < 4f < 5d < 6p < 7s < 5f < 6d < 7p < 8s\n\nWe can easily remember the sequence of energy level from the chart (Fig 3.04) below:\n\nWe have seen, the orbital s can contain a maximum of two electrons, the orbital p can contain a maximum of six electrons, the orbital d can contain a maximum of ten electrons and the orbital f can contain a maximum of fourteen electrons. Following this, we can configure the electrons of the following elements.\n\nK(19) → 1s^2 2s^2 2p^6 3s^2 3p^6 4s^1\nCa(20) → 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2\nSc(21) → 1s^2 2s^2 2p^6 3s^2 3p^6 3d^1 4s^2\nTi(22) → 1s^2 2s^2 2p^6 3s^2 3p^6 3d^2 4s^2\n\nSince the 4s orbital is lower in energy than the 3d orbital, so the 19th electron of Potassium enters 4s instead of 3d. Again, in the case with Scandium, 19th and 20th electrons go inside 4s and then the 21st electron goes to the higher energy 3d orbital.\n\nAlways remember, when writing the electronic configuration, write down all orbitals of an energy level side by side; otherwise there is chance of making mistakes. For example: the configuration of Fe (26) will be\n\nFe(26) → 1s^2 2s^2 2p^6 3s^2 3p^6 3d^6 4s^2", "figures": [ { "caption": "Energy sequence of orbitals", "reference": "Fig 3.04" } ] }, { "title": "3.7.3 Some Exceptions in Electronic Configuration", "text": "Commonly, if the orbital of the energy sublevel p and d are half full (p^3, d^3) or complete (p^6, d^10), that kind of electronic configuration is the most stable. That way, the electronic configuration of Cr(24) is supposed to be Cr(24) → 1s^2 2s^2 2p^6 3s^2 3p^6 3d^4 4s^2. But the desire of 3d^5 to be half full brings one electron from 4s orbital. That way, the chromium electronic configuration stands at Cr(24) → 1s^2 2s^2 2p^6 3s^2 3p^6 3d^5 4s^1." } ] }, { "section": "3.8 Isotopes", "text": "Atoms of the same element with equal number of protons but different numbers of neutrons and mass are called isotopes of each other. The three atoms in the table 3.09 below have the same number of protons. Therefore, they are isotopes of each other. Hydrogen has seven isotopes (1H, 2H, 3H, 4H, 5H, 6H, 7H). Three of them are available in nature and the remaining four are laboratory made.", "tables": [ { "caption": "Table 3.09: Three Natural Isotopes of Hydrogen.", "headers": ["Name", "Symbol", "Proton Number Z", "Mass Number A", "Neutron Number A - Z"], "rows": [ ["Hydrogen or Proteum", "1H", "1", "1", "0"], ["Deuterium", "2D", "1", "2", "1"], ["Tritium", "3T", "1", "3", "2"] ] } ] }, { "section": "3.9 Atomic Mass or Relative Atomic Mass", "text": "We already know that, the mass number of an element's atom is the summation of the number of protons and neutrons present in its nucleus. It certainly implies the idea that the mass number must be an integer. But you will see the atomic mass of copper is 63.5 and the atomic mass of chlorine is 35.5. How is that possible? In fact, it is the relative atomic mass. What is it and why is it necessary?\n\nThe mass of an atom of Fluorine is 3.16 × 10^-23 g\nThe mass of an atom of Aluminium is 4.482 × 10^-23 g\n\nIt is really hard to use such small masses in our practical field. That is why, 1/12 th of a Carbon 12 isotope is taken as a unit and then the atomic mass of other atoms are determined relative to that.\n\n1/12 th atomic mass of Carbon 12 isotope is 1.66 × 10^-24 g\n\nTherefore, the relative atomic mass of the element:", "subsections": [ { "title": "3.9.1 Determining the Average Relative Mass of an Element from Percentage of Isotope", "text": "Most of the elements in nature have more than one isotope. We calculate the average relative mass of those elements having more than one isotope from their percentage of availability in nature. The steps in this calculation are:\n\nStep 1: Multiply the mass numbers of all isotopes of that element with the percentage of natural availability of those isotopes.\n\nStep 2: Get the summation of all the results of step 1.\n\nStep 3: Divide the total of step 2 by 100. This will give the average relative mass of that element.\n\nSuppose, an element A has 2 isotopes. The mass number of an isotope is p and the percentage of this isotope available in nature is m. The mass number of another isotope is q and the percentage of this isotope is n. Then,\n\nThe average relative atomic mass of that element is Ω = (p × m + q × n)/100\n\nExample: There are two isotopes of Chlorine in nature, 35Cl and 37Cl.\n\nNaturally available percentage of 35Cl = 75%\nNaturally available percentage of 37Cl = 25%\n\nSo, the average relative atomic mass of Chlorine = (35×75 + 37×25)/100 = 35.5\n\nIn the periodic table also, you will see that the average relative atomic mass is shown as 35.5. The periodic table displays the average relative atomic mass." }, { "title": "Application of determining the average relative atomic mass of elements", "text": "Determining the percentage of isotopes from the average relative atomic mass of an element: If there are two naturally available isotopes of an element, then we can calculate the percentage of those isotopes available in nature from the average relative atomic mass.\n\nExample: In nature, there are two isotopes of copper. These are 63Cu and 65Cu. The average relative atomic mass is 63.5.\n\nSuppose, the percentage of 63Cu is x% and 65Cu is (100 - x)%\n\nNow, the average relative atomic mass of Copper = (x×63 + (100 - x)×65)/100 = 63.5\nor, x = 75%\n\nNaturally available percentage of 63Cu = 75% and Naturally available percentage of 65Cu = (100 - 75)% = 25%" }, { "title": "3.9.2 Getting the Relative Molecular Mass from Relative Atomic Mass", "text": "We can get the relative molecular mass of an atom by taking the summation of the multiplied value of relative atomic mass of the atoms with their respective number of atoms. Generally, relative atomic mass is considered as atomic mass and relative molecular mass as molecular mass.\n\nExample-1: The atomic mass of Hydrogen (H) atom in a H2 molecule is 1 and it has two atoms, so the relative molecular mass of H2 molecule is 1×2 = 2.\n\nExample-2: In a H2SO4 molecule, the relative atomic mass of H is 1 and number of atoms is 2. The relative atomic mass of Sulfur is 32 and number of atom is 1. The relative atomic mass of Oxygen is 16 and number of atom is 4. Therefore, the relative molecular mass of H2SO4 will be 1×2 + 32×1 + 16×4 = 98." } ] }, { "section": "3.10 Radioactive Isotopes and Their Uses", "text": "We have already learned about isotopes in this chapter. There are some isotopes the nucleus of which spontaneously break themselves and emit various radioactive rays such as alpha (α), beta (β) and gamma (γ) rays. Isotopes of an element that emit radioactive rays are called radioactive isotopes. So far, scientists have gathered information of more than 3000 isotopes. Some of them are natural and some are laboratory made. The physics book for your class discusses about various isotopes and their radioactivity in details. We will only learn about their uses here.\n\nControlled use of radioactive isotopes has made many an impossibility possible. Presently, such isotopes are used in medical science, agriculture, preservation of food and seeds, electricity generation and in determining the age of anything.", "subsections": [ { "title": "3.10.1. Medical Science", "text": "Medical science employs radioactive isotopes for various purposes. For example:\n\nDiagnoses of diseases: We can take pictures of a patient's affected area using radioactive isotopes. Technetium-99 (99Tc) is injected inside the body in this system. When it gathers a particular isotope at a certain place inside the body, the isotope emits gamma rays. The gamma ray identification camera from outside can take the photo of that spot of the body. The lifetime of this radioactive isotope (Technetium-99) is 6 hours. Since it loses its radioactivity within a short time, it is safe.\n\nTreating Diseases: Radioactive isotope was first used to cure thyroid cancer. The patient is made to drink a solution of 131I. This isotope reaches the thyroid and emits beta rays which destroys the affected cells. Iridium isotope is used to treat brain cancer. 60Co isotope is used to diagnose and treat tumors. The gamma rays emitted from this isotope (60Co) destroys the cancer affected cells and tissues. 32P isotope is used for treatment of leukemia." }, { "title": "3.10.2 Agriculture Sector", "text": "Nutrition of Crops: Sufficient fertilizers are required for nutrition of crops. The quantity of fertilizer is an important issue. Excess fertilizer costs more than necessary. It is also harmful for the environment. On the other hand, less than necessary fertilizer will cause less production of crops. Radioactive isotopes help to determine the amount of Nitrogen and Phosphorus present in the soil. Plants absorb radioactive Nitrogen and Phosphorus via its roots which is then transferred to different parts of its body. Geiger Muller Counters help to identify the presence of these isotopes and helps to determine the presence of the two elements in soil. Then we can determine the remedy too.\n\nGetting Rid of Harmful Insects: Harmful insects are always a threat to a good crop. They not only lessen the production of crops but also they introduce various harmful microbes to the plants. We use insecticides to get rid of these insects. These insecticides are harmful for our body and environment as well. These insecticides also kill their insects that are of help for our crops. Insecticides enriched with radioactive isotopes have helped us to determine the standard quantity of insecticides for a particular crop.\n\nQuality Improvement of Crops: Radioactive isotopes also play a significant role in developing hybrid varieties by bringing genetic changes in the original crop." }, { "title": "3.10.3 Generation of Electricity", "text": "A huge amount of heat is generated in fission reactions i.e., breaking some atoms into smaller atoms. Driving this heat energy through generators, we can produce electricity. We call such power plants, nuclear power plants. The fourth chapter of your physics book discusses this in detail.\n\nThe government of Bangladesh has established a nuclear power plant in Rooppur of Pabna. The power plant can produce 2400MW electricity." }, { "title": "3.10.4 Impact of Radioactive Isotope", "text": "It is true that radioactive isotopes have a good number of benefits. But at the same time, they have the potential to harm us too. The alpha, beta and gamma rays emitted from such isotopes can bring about genetic changes to cells which may cause cancer. The atom bombs used in Hiroshima and Nagasaki of Japan during the world war 2 killed lacs of people. The Chernobyl accident of 1986 in Russia has killed numerous people and has done harm to the adjacent environment." } ] } ] }, { "chapter_number": 4, "title": "Periodic Table", "start_page": 59, "end_page": 81, "content": [ { "section": "4.1 Background of Periodic Table", "text": "Periodic table is the outstanding collection of chemical concepts gathered over hundreds of years. It is not an achievement of one single scientist or a one day's effort. Various scientists have given their tireless effort after it to get the present state of the table.\n\nIn 1789, Antoine Lavoisier first divided the elements like Oxygen, Nitrogen, Hydrogen, Phosphorus, Mercury, Zinc, Sulphur etc. into metals and non- metals. Then on, there were constant efforts to divide the elements in groups having the same characteristics.\n\nIn 1829, the scientist Dobereiner found that groups of three elements show the same kind of features. First, he organized the elements into three according to their atomic mass. Then he marked that atomic mass of the second element is half or near about half of the summation of first and third's atomic mass. Dobereiner identified Chlorine, Bromine and Iodine as the first trio of chemical elements. It is known as Dobereiner's Law of Triads.\n\nFor the elements detected up to 1864, English scientist John A R Newlands gave a theory called Law of Octet. According to it, if elements are organized following a sequence of lower to higher atomic mass, there is evident similarity in physical and chemical properties of each eighth element.\n\nIn the year 1869, Russian scientist Mendeleev published a table in an attempt to contain elements with similar properties in the same group. Reviewing the physical and chemical properties, he theorized, 'Physical and chemical properties of elements return periodically as atomic mass of elements increase.'\n\nFollowing this theory, he organized the 63 elements identified till then in eight vertical columns and 12 horizontal lines. Thus he proved that elements belonging to each column have the same physical and chemical properties and in each line, they change gradually as they progress from left to right. The table was named Periodic Table.\n\nAnother success of Mendeleev's table is his correct forecast about the existence of some elements. He kept some cells in his table blank as there were only 63 of them detected till then. Later on, these cells were accommodated by detected elements, proving Mendeleev correct.\n\nThere are some flaws in Mendeleev's table. According to his theory, elements with lesser atomic mass were supposed to be set before the elements with higher atomic mass. However, in Mendeleev's table, Argon with its atomic mass 40 is placed before Potassium with atomic mass 39. He did this to group according to similarity of physical and chemical properties. There are some other cases with similar flaws and other flaws in Mendeleev's table.\n\nIn 1913, scientist Mosley proposed to organize elements according to their atomic number instead of atomic mass. When the table was reorganized according to atomic number of elements, Argon (18) came automatically before Potassium (19) and thus the flaw in Mendeleev's table was corrected.\n\nInternational Union of Pure and Applied Chemistry (IUPAC) has so far detected 118 elements. IUPAC supervises and controls different matters of chemistry and applied chemistry- like creating various rules and regulations, overseeing which of the escalating changes or inventions are to be accepted or discarded etc.\n\nLavoisier started with only 33 elements which became 63 detected and 4 undetected elements in Mendeleev's table. Now, that attempt has turned out to be the modern periodic table with 118 detected elements." }, { "section": "4.2 Characteristics of the Periodic Table", "text": "The periodic table is basically a table of elements. It also features columns and rows. In the periodic table, the rows from left to right are called Periods and vertical columns are called Groups. There are a total of 118 elements accommodated in the cells of the table, which is there for you at the beginning of this chapter.\n\nThe modern periodic table has some prominent characteristics. You can find these features if you take a closer look at the table.\n\na. There are seven periods (horizontal rows) and 18 groups (vertical columns) in the periodic table.\nb. All periods start with group 1 at the extreme left and extend up to group 18 at the extreme right.\nc. A small table of 2 horizontal rows and 14 columns displays the Lanthanide and Actinide elements beneath the main periodic table. These are part of period 6-7 of the main periodic table.\nd. Period 1 contains only two elements. Periods 2 and 3 contain eight elements each. Period 4 and 5 contain 18 elements each. Periods 6 and 7 contain 32 elements each.\ne. Group 1 contains 7 elements. Group 2 contains 6 elements. Group 3 has 32 elements. Groups 4 to 12 contain 4 elements each. Groups 13-17 have 6 elements each. Group 18 contains 7 elements.\n\nFifteen elements with atomic numbers 57 to 71 are called the Lanthanide elements. Fifteen elements with atomic numbers 89 to 103 are categorized as Actinide elements. Physical and chemical properties of elements belonging to each of these two categories are so close that they have been put separately in two separated rows.\n\nNow consider the periodic table in terms of properties of elements.\n\n1. Properties of elements gradually change from left to right in the same period.\n2. The physical and chemical properties of elements of the same group are almost similar." }, { "section": "4.3 Determination of the Position of Elements in the Periodic Table from Their Electronic Configuration", "text": "We can easily determine the group and period of an element from the electronic configuration of that element. The system of finding out the place of an element in the periodic table is discussed below:\n\nDetermining the Period Number: The number of the outermost main energy level in the electronic configuration of an element is the period number of that element. For example: the electronic configuration of Lithium is Li(3) → 1s^2 2s^1. Since the outermost energy level of Lithium is 2 so the element belongs to the period 2 of the table. In the same way, the electronic configuration of Potassium is K(19) → 1s^2 2s^2 2p^6 3s^2 3p^6 4s^1. Since the outermost energy level of Potassium is 4, so the element belongs to the period 4 of the table.\n\nDetermining the Group: The group number of an element can be determined in a number of ways.\n\nSystem 1: If the outermost energy level of an element consists of s orbital only, the total number of electrons in that s orbital is the group number of that element. The electronic configuration of Hydrogen, H(1) is 1s^1. Since the outermost energy level of Hydrogen consists of s orbital and it contains only 1 electron, so the element belongs to the group 1 of the table.\n\nSystem 2: If the outermost energy level of an element consists of s and p orbitals only, the total number of electrons in those s and p orbitals added with 10 is the group number of that element. The electronic configuration of Boron is B(5) - 1s^2 2s^2 2p^1. Since the outermost energy level of Boron consists of s orbital with 2 electron and p orbital with 1 electron, so the element belongs to the group 3 + 10 = 13 of the table.\n\nSystem 3: If the outermost energy level of an element consists of an s orbital which is preceded by a d orbital in the inner level, the total number of electrons in those s and d orbitals is the group number of that element. The electronic configuration of Fe is Fe(26) → 1s^2 2s^2 2p^6 3s^2 3p^6 3d^6 4s^2. Since the outermost energy level of Iron consists of s orbital with 2 electron and is preceded by a d orbital with 6 electrons, so the element belongs to the group 8 of the table. To make it easier for you to understand, the electronic configuration of the outer most energy level has been denoted by red colour.", "tables": [ { "caption": "Table 4.01: Electronic Configuration of Elements and their Groups", "headers": ["Element", "Electronic Configuration", "Period Number", "Group Number"], "rows": [ ["H(1)", "1s1", "1", "1 (System 1)"], ["He(2)", "1s2", "1", "18 (Exception)"], ["Li(3)", "1s2 2s1", "2", "1 (System 1)"], ["Be(4)", "1s2 2s2", "2", "2 (System 1)"], ["B(5)", "1s2 2s2 2p1", "2", "2 + 1 + 10 = 13 (System 2)"], ["C(6)", "1s2 2s2 2p2", "2", "2 + 2 + 10 = 14 (System 2)"], ["N (7)", "1s2 2s2 2p3", "2", "2 + 3 + 10 = 15 (System 2)"], ["O(8)", "1s2 2s2 2p4", "2", "2 + 4 + 10 = 16 (System 2)"], ["F(9)", "1s2 2s2 2p5", "2", "2 + 5 + 10 = 17 (System 2)"], ["Ne(10)", "1s2 2s2 2p6", "2", "2 + 6 + 10 = 18 (System 2)"], ["Na(11)", "1s2 2s2 2p6 3s1", "3", "1 (System 1)"], ["Mg(12)", "1s2 2s2 2p6 3s2", "3", "2 (System 1)"], ["Al(13)", "1s2 2s2 2p6 3s2 3p1", "3", "2 + 1 + 10 = 13 (System 2)"], ["Si(14)", "1s2 2s2 2p6 3s2 3p2", "3", "2 + 2 + 10 = 14 (System 2)"], ["P (15)", "1s2 2s2 2p6 3s2 3p3", "3", "2 + 3 + 10 = 15 (System 2)"], ["S (16)", "1s2 2s2 2p6 3s2 3p4", "3", "2 + 4 + 10 = 16 (System 2)"], ["Cl(17)", "1s2 2s2 2p6 3s2 3p5", "3", "2 + 5 + 10 = 17 (System 2)"], ["Ar(18)", "1s2 2s2 2p6 3s2 3p6", "3", "2 + 6 + 10 = 18 (System 2)"], ["K(19)", "1s2 2s2 2p6 3s2 3p6 4s1", "4", "1 (System 1)"], ["Ca(20)", "1s2 2s2 2p6 3s2 3p6 4s2", "4", "2 (System 1)"], ["Sc(21)", "1s2 2s2 2p6 3s2 3p6 3d1 4s2", "4", "2 + 1 = 3 (System 3)"], ["Ti(22)", "1s2 2s2 2p6 3s2 3p6 3d2 4s2", "4", "2 + 2 = 4 (System 3)"], ["V(23)", "1s2 2s2 2p6 3s2 3p6 3d3 4s2", "4", "2 + 3 = 5 (System 3)"], ["Cr(24)", "1s2 2s2 2p6 3s2 3p6 3d5 4s1", "4", "1 + 5 = 6 (System 3)"], ["Mn(25)", "1s2 2s2 2p6 3s2 3p6 3d5 4s2", "4", "2 + 5 = 7 (System 3)"], ["Fe(26)", "1s2 2s2 2p6 3s2 3p6 3d6 4s2", "4", "2 + 6 = 8 (System 3)"], ["Co(27)", "1s2 2s2 2p6 3s2 3p6 3d7 4s2", "4", "2 + 7 = 9 (System 3)"], ["Ni(28)", "1s2 2s2 2p6 3s2 3p6 3d8 4s2", "4", "2 + 8 = 10 (System 3)"], ["Cu(29)", "1s2 2s2 2p6 3s2 3p6 3d10 4s1", "4", "1 + 10 = 11 (System 3)"], ["Zn (30)", "1s2 2s2 2p6 3s2 3p6 3d10 4s2", "4", "2 + 10 = 12 (System 3)"] ] } ] }, { "section": "4.4 Electronic Configurations of Elements are the Main Basis of the Periodic Table", "text": "Electronic configuration serves to identify the group and period of an element in the periodic table. Again, elements having the same electron arrangement in their outermost orbit belong to the same group. On the other hand, elements with different configuration of electrons in their outermost shell belong to separate groups.", "tables": [ { "caption": "Table 4.02: Group and Electronic Configuration", "headers": ["Group 1", "Group 2"], "rows": [ ["Element", "Electronic Configuration", "Element", "Electronic Configuration"], ["H(1)", "1s1", "He(2)", "1s2"], ["Li(3)", "1s2 2s1", "Be(4)", "1s2 2s2"], ["Na(11)", "1s2 2s2 2p6 3s1", "Mg(12)", "1s2 2s2 2p6 3s2"], ["K(19)", "1s2 2s2 2p6 3s2 3p6 4s1", "Ca(20)", "1s2 2s2 2p6 3s2 3p4 4s2"] ] } ], "text": "The elements with one electron in the outer shell generally tend to give away the electron and become positive ions. For example, Sodium has one electron in its outer shell. So, it donates the electron and becomes a positive ion.\n\nNa(1s2 2s2 2p6 3s1) → Na+(1s2 2s2 2p6) + e-\n\nAgain, elements with seven electrons in the outer shell generally tend to accept an electron and become negative ions. For example, Chlorine has seven electrons in its outer shell. So, it accepts one electron and becomes a negative ion.\n\nCl(1s2 2s2 2p6 3s2 3p5) + e- → Cl-(1s2 2s2 2p6 3s2 3p6)\n\nSo, electronic configuration helps us to determine the position of an element in the periodic table and explain their various characteristics as well. Therefore, electronic configuration is considered as the main basis of the periodic table." }, { "section": "4.5 Some Exceptions in the Periodic Table", "text": "a. Position of Hydrogen: Hydrogen is a non-metal. However, the periodic table displays hydrogen alongside strong electropositive alkali metals like Na, K, Rb, Cs, Fr etc. in group 1. It is because the outer shell of H contains only 1 electron like the alkali metals. Besides, many properties of Hydrogen are similar to those of alkali metals. On the other hand, Hydrogen is also able to accept an electron like the Halogen elements (F, Cl, Br, I), meaning it has some similarities with Halogen in terms of properties. However, since most of the properties of Hydrogen have similarity with alkali metals, it is placed alongside the alkali metals in group 1.\n\nb. Position of Helium: The electronic configuration of Helium is He(2) → 1s2. According to its configuration, it was supposed to be positioned in group 2. But the elements of group 2 are strongly electropositive. They are called alkaline earth metals. On the other hand, Helium is an inert gas. Its properties are similar to other inert gases like Neon, Argon, Krypton, Xenon and Redon. And its properties are not at all similar to the alkaline earth metals. Therefore, Helium is placed alongside the inert gases in group 18.\n\nc. Position of Lanthanide and Actinide Groups: The Lanthanide elements are supposed to be set in the period 6 and group 3 of the periodic table. The original position of Actinide group is in period 7 and group 3. If they are placed in these positions, that hampers the beauty of the table. Therefore, to maintain the beauty of the table, these two groups of elements are moved to a separate table just beneath the main table." }, { "section": "4.6 Periodic Properties of Elements", "text": "The elements in the periodic table have some properties, like: metallic properties, non- metallic properties, atomic radius, ionization energy, electro negativity, electron affinity etc. These properties are called periodic properties.\n\na. Metallic Property: Elements which are glossy, produce metallic sound when struck, and conductor to heat and electricity, we call them metals. Modern definition goes, the elements that turn into positive ions donating one or more electrons are metals. This property to donate electrons by the metals is called metallic property. The more an element is prone to donate electrons it is regarded to be endowed with more metallic property. For example, Lithium (Li) is a metal as it donates an electron and becomes Li+.\n\nLi → Li+ + e-\n\nAny period in the periodic table has got the most metallic on the left and gradually elements are less metallic as the period extends to the right.\n\nb. Non-metallic Property: Elements which are not glossy, do not produce metallic sound and non conductor of heat and electricity are called non-metallic. In the modern terminology, the elements which turn into negative ions accepting one or more electrons are called non-metallic elements. This tendency to accept electrons is called their non-metallic property. The more an element is prone to accept electrons it is regarded to be endowed with more non-metallic property. For example, Chlorine (Cl) is a non-metal as it accepts an electron and becomes Cl-.\n\nCl + e- → Cl-\n\nAny period in the periodic table becomes more non- metallic as it extends to the right.\n\nSome elements are there which sometimes behave like metals and sometimes behave like non- metals. They are called sub- metals. According to modern definition, elements that sometimes tend to donate electrons and sometimes accept electrons are called sub- metals. For example, Silicon (Si) is a sub metal.\n\nIn the periodic table, the left periods are metals, middle periods are sub metals and the right side periods are non- metals.\n\nc. Atomic Radius/ Size of Atom: The size of atom or the atomic radius is a periodic property. The more a period progresses from left to right, the size of atom/atomic radius decreases. Again, vertically in the periodic table, the lower we go from the upper part, the size of atom increases.\n\nIn a period, the more we move from left to right, the atomic number increases, but the shell number remains unchanged. As the atomic number increases, number of protons in the nucleus increases and so do the number of electrons. The attraction between the increased number of electrons and protons resulting in the electron containing shells getting closer to the nucleus. As a result, the atomic radius decreases.\n\nAgain, in a same group, the lower we move from the upper part, a new shell is added to the outer layer. These added shells increase the size of the atom.\n\nNoteworthy that, newer shells increase the size of atom more than the added electrons and protons decrease the size. That is why, the lower part of the periodic table contains elements with bigger atoms.", "figures": [ { "caption": "Periodic property of atomic radius", "reference": "Fig 4.01" }, { "caption": "Ionization of element", "reference": "Fig 4.02" } ] }, { "section": "4.7 The Special Names of Elements Present in Various Groups", "text": "Elements were bestowed with special names at different times based on their physical and chemical properties. Apart from metals, non- metals and sub metals already discussed, there are also some others.\n\nAlkali Metals: There are seven elements in Group- 1 of the table. Apart from Hydrogen, the six other elements here (Lithium, Sodium, Potassium, Rubidium, Cesium and Francium) are called alkali metals. Since all of them are soluble in water and produce hydrogen gas and alkali. This is why, they are called Alkali Metals.\n\nAlkaline Earth Metals: There are 6 elements in Group 2 of the periodic table- Beryllium, Magnesium, Calcium, Strontium, Barium and Radium. These elements are called alkaline earth metals. They are available as various compounds in soil and all of them produce alkali. That is why, they are grouped under alkaline earth metals.\n\nCoin Metals: Copper, Silver, Gold and Rontzanium are four metals belonging to Group- 11. The first three of them are called coin metals as they were used to produce coins from the ancient age and were used as a means of trade and commerce.\n\nHalogen Group: Six elements of Group- 17 are called Halogens. They are Fluorine, Chlorine, Bromine, Iodine, Astatine and Tennessee. These Halogen elements are expressed by X. The meaning of Halogen is salt maker and its main source is sea- salt. Metals bonding with these elements produce salts, like Na and F bond together to produce Sodium Fluoride or Na and Cl together produce Sodium Chloride or mineral salt. They themselves form di- atomic molecules by sharing electrons, like Cl2, I2, etc.\n\nInert Gas: Elements belonging to Group- 18 are called inert gases. They are Helium, Neon, Argon, Krypton, Xenon, Redon and Oganeson. As their outermost energy level is filled with required electrons, they do not show any tendency to form compounds by accepting, donating or sharing electrons. This inaction in chemical reaction or chemical bonds gives them their group name inert elements or inert gases. They remain in gaseous form at normal temperature.\n\nTransition Elements: Transition elements are also known as transition metals because all of them are metals. Transition elements belong to the d- block of the periodic table. However, not all d- block elements are considered transition elements. Only those d- block elements whose one or more orbitals are partially filled with electrons are classified as transition elements. For example- iron (Fe), nickel (Ni), and chromium (Cr), etc. Transition elements have some special characteristics. For example, they exhibit multiple oxidation states in compounds, they generally form coloured compounds, and they often act as good catalysts in industrial processes. You will learn more about them in your higher secondary classes." }, { "section": "4.8 Advantages of the Periodic Table", "text": "The periodic table is a highly significant contribution of various chemists of different ages. Practice of chemistry is not possible without the modern periodic table. Some of the advantages of this chart are presented below.\n\na. Simplifying Study of Chemistry: We know that a total of 118 elements have been identified till 2016. If we consider only four physical properties (melting point, boiling point, density and state of matter) and four chemical properties (reaction with Oxygen, water, acid and alkali), then that turns out 118 × (4 + 4) = 944 properties for these elements. It is impossible to remember all this information. The periodic table has simplified that task. The periodic table has 18 groups (Vertical columns) and 7 periods (horizontal rows). If we know the common properties belonging to each group in the table, we will also be aware of the physical and chemical properties of all 118 elements. Again, since we will be familiar with the common properties of elements, we will also know the properties of compounds made with them.\n\nb. Detection of New Elements: there were some blank cells in the periodic table even some decades ago. The periodic table gave us prior idea about the elements that will be accommodating those cells and their properties even before they were detected. You have already known that, the elements predicted by the scientist Mendeleev while arranging the 63 known elements of his time in his periodic table were later discovered.\n\nc. In Research: The periodic table has a large contribution in the field of research too. Suppose, a scientist is interested to invent a new matter to meet up a specific purpose. In that case, he must have some conception about what the properties would be of the new matter and what kind of elements will be able to produce the new matter. He will get this idea from the periodic table.\n\nYou will gradually come to know about the other advantages of the periodic table." }, { "section": "4.9 Elements in the Same Group in the Periodic Table Show Similar Chemical Properties", "text": "An experiment will tell you that elements of the same group exhibit the same kind of properties.\n\nThe gases F2, Cl2, Br2, I2 etc. belonging to Group- 17 react with Hydrogen and produce HF (g), HCl (g), HBr (g), HI (g) gases respectively.\n\nH2(g) + F2(g) → 2HF(g)\nH2(g) + Cl2(g) → 2HCl(g)\nH2(g) + Br2(g) → 2HBr(g)\nH2(g) + I2(g) → 2HI(g)\n\nAgain, if we dissolve these produced gases into water, they produce hydrohalide acids, i.e. Hydrofluoric acid [HF(aq)], Hydrochloric acid [HCl(aq)], Hydrobromic acid [HBr(aq)], Hydroiodic acid [HI(aq)].\n\nHF(g) + H2O(l) → HF(aq)\nHCl(g) + H2O(l) → HCl(aq)\nHBr(g) + H2O(l) → HBr(aq)\nHI(g) + H2O(l) → HI(aq)\n\nThese hydrohalide acids react with any carbonate salt and produce Carbon dioxide gas, e.g. Calcium Carbonate and Hydrofluoric acid produce Carbon dioxide:\n\nCaCO3 + 2HF(aq) → CaF2 + H2O + CO2\n\nIn the same way, Calcium Carbonate and Hydrochloric acid produce Carbon dioxide:\n\nCaCO3 + 2HCl(aq) → CaCl2 + H2O + CO2\n\nSo, the above reactions convince you that the elements (F2, Cl2, Br2, I2) of Group- 17 exhibit the same properties and reactions. Mg and Ca of Group- 2 also exhibit the same properties and reactions.\n\nMagnesium Carbonate (MgCO3) in its reaction with dilute Hydrochloric acid produces Magnesium Chloride, water and Carbon dioxide gas. Calcium Carbonate (CaCO3), in the same reaction produces Calcium Chloride, water and Carbon dioxide gas.\n\nMgCO3 + 2HCl → MgCl2 + H2O + CO2\nCaCO3 + 2HCl → CaCl2 + H2O + CO2" }, { "section": "Experiment", "text": "Name of Experiment: Identifying Carbon dioxide gas in the reaction between Calcium Carbonate and light Hydrochloric acid.\n\nPrinciple: Calcium Carbonate and dilute Hydrochloric acid produce Calcium Chloride, water and Carbon dioxide gas.\n\nCaCO3 + 2HCl → CaCl2 + H2O + CO2\n\nApparatus: a. one conical flask b. a thistle funnel c. a u- shaped delivery tube made of glass d. some gas jars e. cork with bore.\n\nChemicals: Calcium Carbonate, dilute hydrochloric acid and water", "figures": [ { "caption": "Preparation of carbon dioxide", "reference": "Fig 4.03" } ], "text": "1. Take some small pieces of calcium carbonate in the round bottom flask.\n\n2. Using a cork, thistle funnel is inserted into one opening of a flask and one end of an out let tube bent at two right angles is inserted through the other opening.\n\n3. Put in some water in the round bottom flask through the thistle funnel so that the chemicals within and the edge of the thistle funnel remain submerged.\n\n4. Set the other end of the exhaust tube inside a gas jar.\n\n5. Now, slowly add dilute hydrochloric acid through the thistle funnel. You will see, the Carbon dioxide gas bubbles are coming out through the exhaust tube produced in the reaction between Calcium Carbonate and Hydrochloric acid.\n\n6. Let's preserve the Carbon dioxide gas in the gas jar. Since the Carbon dioxide gas is heavier than the other gases in the air, it will gather in the lower part of the jar.\n\nChecking the Properties of Carbon Dioxide Gas:\n\n1. Let's check the colour of the produced Carbon dioxide gas in the jar. It is colourless like carbon dioxide.\n2. Let's hold a lighted matchstick on the open face of the gas jar. It will be extinguished. It is decided that Carbon dioxide helps to extinguish fire.\n3. Let's pass the produced Carbon dioxide gas inside a test tube containing lime water or Calcium hydroxide. First, a small quantity of gas will enter the tube and having reaction with Calcium hydroxide create white Calcium Carbonate residue at the base. The lime water turns cloudy. Now pass more Carbon dioxide gas into the solution. Due to reaction between Calcium Carbonate, water and Carbon dioxide, this will produce Calcium bicarbonate which will clear the lime water.\n\nCaution:\n\n1. Measures were taken so that the end of the thistle funnel was always submerged in the water.\n2. The round-base flask was fixed with a stand.\n\nThe same experiment can be done with snails, oysters, egg shells as substitute for calcium carbonate and vinegar substituting for hydrochloric acid." } ] }, { "chapter_number": 5, "title": "Chemical Bond", "start_page": 82, "end_page": 108, "content": [ { "section": "5.1 Valence Electrons", "text": "The number of total electrons in the outermost principal energy level of an element is called the valence electrons of that element. For example, the electronic configuration of Potassium and Oxygen show 1 and 6 electrons at their outermost energy level.\n\nTherefore, K (Potassium) has 1 valence electron while O (Oxygen) has 6 valence electrons.", "tables": [ { "caption": "Table 5.01: Valence Electrons of Elements.", "headers": ["Element", "K Orbit", "L Orbit", "M Orbit", "N Orbit", "Valence Electron"], "rows": [ ["N(7)", "2", "5", "", "", "5"], ["F(9)", "2", "7", "", "", "7"], ["P(15)", "2", "8", "5", "", "5"], ["Cl(17)", "2", "8", "7", "", "7"], ["Ca(20)", "2", "8", "8", "2", "2"] ] } ], "figures": [ { "caption": "Valence electron of potassium and oxygen", "reference": "Fig 5.01" } ] }, { "section": "5.2 Valency", "text": "You already know that, atoms of different elements donate, accept or share electrons of their outermost energy level with atoms of other elements to form molecules. The capacity of bonding of an atom with another atom of an element while forming a molecule is called valency.\n\nUsually, the valency of Hydrogen is taken to be 1. Valency of an element is determined by the number of H atoms or Cl atoms can bond with one of its atoms.\n\nAn atom of Hydrogen bonds with another atom of Chlorine to form a HCl molecule. So the valency of Chlorine is also 1. Again, an atom of Oxygen bonds with 2 Hydrogen atoms to produce H2O. So valency of Oxygen is 2. 1 atom of Na bonds with 1 Cl atom to produce NaCl, therefore, the valency of Na is 1.\n\nThe number of oxygen atoms that can be bonded with an atom multiplied by 2 determines the valency of that atom. For example, a Calcium atom (Ca) bonds with one Oxygen atom (O) to produce Calcium oxide (CaO). Therefore, the valency of calcium is 1×2 = 2.\n\nSome elements have more than one valency. This kind of valency is called variable valency. For example, variable valency of Fe are 2 and 3. The difference between the highest valency of an element and its active valency is considered as latent valency. For example, in the compound FeCl2, the active valency of Fe is 2 while its highest valency is 3. Therefore, the latent valency of Fe in FeCl2 is (3 - 2) = 1. Again, in FeCl3, the active valency of Fe is 3, and the highest valency of Fe is also 3. Therefore, in this case, there is no latent valency of Fe.", "tables": [ { "caption": "Table 5.02: Valency of Different Elements", "headers": ["Element", "Valency"], "rows": [ ["H", "1"], ["F", "1"], ["Cl", "1"], ["Br", "1"], ["I", "1"] ] }, { "caption": "Table 5.03: Valency and Compounds of Various Atoms", "headers": ["Element", "Valency", "Metallic and Non metallic Atom", "Symbol", "Valency", "Compound"], "rows": [ ["Na", "1", "Hydrogen", "H", "1", "HCl"], ["K", "1", "Silver", "Ag", "1", "AgCl"], ["C", "2, 4", "Lithium", "Li", "1", "LiCl"], ["Mg", "2", "Fluorine", "F", "1", "NaF"], ["Al", "3", "Sodium", "Na", "1", "NaCl"], ["", "", "Potassium", "K", "1", "KCl"], ["", "", "Bromine", "Br", "1", "NaBr"], ["", "", "Iodine", "I", "-1", "NaI"], ["", "", "Magnesium", "Mg", "2", "MgCl2"], ["", "", "Calcium", "Ca", "2", "CaCl2"], ["", "", "Boron", "B", "3", "BCl3"], ["", "", "Aluminum", "Al", "3", "AlCl3"], ["", "", "Phosphorus", "P", "-3", "PCl3"], ["", "", "Iron", "Fe", "2", "FeCl2"], ["", "", "Copper", "Cu", "1", "CuCl"], ["", "", "", "", "3", "FeCl3"], ["", "", "", "", "-2", "CuCl2"], ["", "", "Zinc", "Zn", "2", "ZnCl2"], ["", "", "Oxygen", "O", "2", "H2O"], ["", "", "Carbon", "C", "2", "CO"], ["", "", "", "", "4", "CH4"], ["", "", "Nitrogen", "N", "3", "NH3"], ["", "", "Sulfur", "S", "2", "H2S"], ["", "", "", "", "5", "N2O5"], ["", "", "", "", "4", "SO2"], ["", "", "", "", "6", "SO3"] ] } ] }, { "section": "5.3 Radicals and Their Valencies", "text": "When atoms or ions of multiple elements combine with each other, they form a cluster of atoms that carries positive or negative charges and act as an ion of an element. They are called radicals.\n\nRadicals may be of positive or negative charge. The number of charge of the radicals is their valency. For example, three H atoms and one H+ combine with one N atom to produce the radical named Ammonium (NH4+) ion. Since its number of charge is +1, so its valency is also 1. Charge may be positive or negative but valency is always the number only. It does not have a positive or negative sign.", "tables": [ { "caption": "Table 5.04: Radicals and Their Valencies", "headers": ["Radical", "Formula", "Charge", "Valency"], "rows": [ ["Ammonium", "NH4+", "+1", "1"], ["Carbonate", "CO3--", "-2", "2"], ["Hydrogen Carbonate", "HCO3-", "-1", "1"], ["Sulfate", "SO4--", "-2", "2"], ["Hydrogen Sulfate", "HSO4-", "-1", "1"], ["Sulfite", "SO3--", "-2", "2"], ["Nitrate", "NO3-", "-1", "1"], ["Nitrite", "NO2-", "-1", "1"], ["Phosphate", "PO4--", "-3", "3"], ["Hydroxide", "OH-", "-1", "1"], ["Phosphonium", "PH4+", "+1", "1"] ] } ] }, { "section": "5.4 Chemical Formula of Compounds", "text": "A molecule of a compound is represented using the symbols and numbers of the atoms it contains. For instance, two hydrogen (H) atoms and an oxygen (O) atom combine into a molecule of water (H2O). Here, H2O is the chemical formula of water's molecule. Therefore, a chemical formula is the way of expressing the compound molecule through the symbols, formulas and the numbers of atoms of elements and radicals. The numbers of atoms and radicals present in the molecule are written in subscript.", "subsections": [ { "title": "Rules for Writing Chemical Formula", "text": "a. The number of atoms there are in an element's molecule has to be written in English numerals as a small subscript to the lower right of the elements symbol. Since nitrogen molecule has two atoms, its formula is N2. One molecule of Ozone has 3 oxygen atoms, so its formula is O3. Some elements do not form any molecule. They are expressed through their symbols only. For example- all metals. That way, iron is written as Fe only. Similarly, inert gases do not form molecules, as in Helium, He.\n\nb. Sometimes, a compound's molecule is made of atoms of two different elements. If their valency is not divisible by a common number, then, the symbols of both the elements are written side by side and each is followed by the valency of the other. For example, valency of aluminium is 3 and oxygen is 2. These numbers are not divisible by a common number. In the case with any compound consisting of these two elements, first goes the symbol of aluminium (Al), followed by the valency of oxygen (2). Then the symbol of oxygen (O) comes followed by the valency of aluminium (3). An example is Al2O3. In the same way, valencies of calcium and chlorine are 2 and 1 respectively. The formula of calcium chloride is supposed to be Ca1Cl2. Since, 1 doesn't need mention, so we write, CaCl2. Again, valencies of magnesium and phosphate are 2 and 3 respectively. Therefore, the formula of magnesium phosphate is Mg3(PO4)2. Noteworthy that if a radical is there in a number more than 1, then the formula of the radical goes inside first bracket along with its number and the valency of the other element follows outside the bracket. For example, ammonium phosphate (NH4)3PO4, aluminium sulfate Al2(SO4)3 etc." } ] }, { "section": "5.6 Octet and Duet Rules", "text": "All elements tend to make the electronic configuration of inert gases at their outermost energy level. All inert gases other than helium have 8 electrons at their outermost energy level. When constituting a molecule, an element obtains the electronic configuration of inert gases, holding electrons by means of donating, accepting or sharing electrons. This is known as the octet rule. The central atom C of CH4 molecule has 8 electrons in its outermost energy level. Four of these eight electrons are carbon's own while the rest four comes from hydrogen (figure 5.02). In this way, atoms form compounds by achieving 8 electrons in their outer most shell through the octet rule.\n\nDue to some limitations of the octet rule, scientists have presented a new rule, which is called the 'Duet rule'. This new rule is more modern than the octet rule and it has better utility too. Very much like the inert gases having 2 or 8 electrons at their outermost energy level, when constituting a molecule, atoms will have one or more pairs of electrons at their outermost energy level. This is the duet rule. This means, any molecule's atom will bear one or more pairs of electrons at their outermost energy level.\n\nThe Be atom at the centre of BeCl2 has 2 pairs or 4 electrons at its outermost energy level. B atom at the centre of BF3 has 3 pairs or 6 electrons at its outer most energy level. The C atom at the centre of CH4 has 4 pairs or 8 electrons at its outermost energy level. On the other hand, each of the atoms of N in N2 has 3 pairs or 6 electrons in its outermost energy level.\n\nSo, duet rule is a more modern and wider version of the octet rule. Many compounds follow only the duet rule. That is why the duet rule is more acceptable than the octet rule." }, { "section": "5.8 Chemical Bonds and the Causes of their Formation", "text": "Two hydrogen atoms mutually bond together into hydrogen (H2) molecule. Similarly, atoms of hydrogen and chlorine bond with each other to constitute hydrogen chloride (H-Cl) molecule. In hydrogen molecule, a kind of attractive force is effective among the two H atoms. In hydrogen chloride also, there is an attractive force working among the H and Cl atoms. Basically, this kind of attractive force is a chemical bond, meaning the attraction force that forces the atoms to stay together is called a chemical bond. This raises two questions- why do not the atoms stay separate and why do they bond together to create the molecule?\n\nWe have already learned that all elements tend to form the stable electronic configuration of inert gases at their outermost energy level. When two atoms of the same element or different element stay close to each other, they accept, donate, or share electrons to complete their outermost shell and achieve the stable configuration of the nearest inert gas. Thus, they create a kind of attraction among themselves, we call it a chemical bond. Therefore, it can be said that the main reason of chemical bonds is the tendency of the atoms to assume stability of electronic configuration at their outermost energy level." }, { "section": "5.9 Cations and Anions", "text": "We know, under normal situations, the number of positively charged protons in the nucleus of an atom is equal to the number of negatively charged electrons outside its nucleus. As a result, the atom becomes charge neutral. If one or more electrons from the outer energy level is removed from such a charge neutral atom, its neutrality will no longer exist. Then, it will turn into an ion with positive charge. Such an ion with positive charge is called a cation. Usually, the elements or metals at the left side of periodic table donate one or more electrons from their outermost energy level to gain the electronic configuration of inert gases and become cations. For example, a lithium atom donates one electron from its outermost energy level in order to get the configuration like helium and produces a lithium cation (Li+). The figure below shows it.\n\nSimilarly, the Na atom donates an electron from its outermost energy level in order to get the configuration like neon gas and produces the Sodium cation (Na+). (Fig: 5.04)\n\nCan you tell why the metals donate electrons from their outermost shell to produce cations? We know, in any period of the periodic table, elements gradually lose their metallic property as we progress from left to right. Simultaneously, the non-metallic property increases in them in this case. It means the elements on the left side of a period are metals and on the right side are non-metals. Again the more rightward we progress in a period; the size of atom also decreases. Therefore, metals generally have larger atomic sizes than the other elements in the same period. The outermost energy level of metals usually contains 1, 2 or 3 electrons. Due to the bigger size of the metals, the outermost energy level electrons is comparatively far from their nucleus which implies a weaker attraction force towards the nucleus or a weaker bond. As a result, their ionization energy is far lower. As a result, if a bit of force is applied, these metals donate one or more electrons from their outermost energy level attain the stable inert gas configuration, and turn into cations.\n\nOn the other hand, the non-metals do not create cations. Now you can probably guess the reason for this. Non-metals are located at the right side of the periodic table. They usually have 5, 6 or 7 electrons in their outermost energy level. Being smaller than metals in their size, the outermost energy level of these elements stay comparatively closer to their nucleus and undergo stronger attractive force. That means their ionization energy is also higher. It requires a stronger force to remove one or more electrons from such elements which is not there in a normal chemical reaction. That is why the non-metals usually do not create cations.\n\nThen, do non-metals undergo any changes in the outermost energy level? Yes, since their outermost energy level usually lacks 1, 2 or 3 electrons to become an octet, they easily accept them from other elements and assume the stable electronic configuration of their nearest inert gas. In other words, their electron affinity is high. This acceptance of electrons from other elements increases the number of negatively charged electrons than the number of positively charged protons in them. Thus, in general, the atoms of non-metals are negatively charged. These negative charge non-metal atoms are known as anions. For example, the Cl atom accepts one electron to reach the electronic configuration of inert argon (Ar) gas and thus produces chloride a (Cl-) ion. (Fig 5.05)", "figures": [ { "caption": "Formation of cation Lithium (Li)", "reference": "Fig 5.03" }, { "caption": "Formation of sodium cation (Na+)", "reference": "Fig 5.04" }, { "caption": "Formation of chloride anion (Cl)", "reference": "Fig 5.05" } ] }, { "section": "5.10 Ionic Bond or Electrovalent Bond", "text": "We have already learned that the metals having lower ionization energy easily lose one or more electrons from their outermost energy level and turn into positively charged cations. On the other hand, the non-metals having higher ionization energy easily receive electrons into their outermost energy level and turn into negatively charged anions. When such oppositely charged cations and anions are formed, a strong electrostatic force of attractions acts between them. This electrostatic or Coulomb force keeps them together. The attractive force by which cations and anions, formed by exchanging electrons, are held within the atoms of a compound is called the ionic bond. For example, Na atom donates one electron from its outermost energy level to attain the electronic configuration of a inert gas. By doing so, it forms the Na+ cation with its 8 electrons in the outermost energy level. On the other hand, Cl atom receives one electron donated by Na in its outermost energy level and forms Cl- anion with its 8 electrons in the outermost energy level. These two mutually opposite charges the positively charged Na+ and the negatively changed Cl- are attracted towards each other in a bond of electrostatic force. This attraction force is the ionic bond. In other words, when there is a chemical bonding between a metal atom and a non-metal atom, the metal atom transfers one or more electrons from its outermost energy level to the outermost level of the non-metal atom. This transfer creates positively and negatively charged ions and the bond formed between them is called ionic bond. The compound that has an ionic bond is called an ionic compound.\n\nIn the MgO molecule, Mg donates 2 electrons to get the electronic configuration of Ne and become Mg2+ with 8 electrons at the outermost energy level.\n\nMg → Mg2+ + 2e-\n\nThe O atom accepts those 2 electrons to get the electronic configuration of Ne and become O2- with 8 electrons at the outermost energy level.\n\nNow, Mg2+ and O2- come closer to form an ionic bond. MgO is an ionic compound.\n\nIn the NaH molecule, Na atom donates an electron to get the electronic configuration of inert gas and becomes Na+ with 8 electrons at the outermost energy level.\n\nThe H atom accepts that electron to get the electronic configuration of an inert gas and become H- with 2 electrons at the outermost energy level.\n\nNa → Na+ + e-\nH + e- → H-\n\nNow, Na+ and H- come closer to form an ionic bond.\n\nIn the CaO molecule, Ca atom donates two electrons to get the electronic configuration of inert gas and becomes Ca2+ with 8 electrons at the outermost energy level.\n\nCa → Ca2+ + 2e-\n\nThe O atom accepts those electrons to get the electronic configuration of inert gas and become O- with 8 electrons at the outermost energy level.\n\nO + 2e- → O2-\n\nNow, Ca2+ and O2- come closer to form an ionic bond.\n\nNotably, the metals belonging to Group 1 and 2 and the non-metals of Group 16 and 17 of the periodic table usually commit themselves to ionic bonding. Each rule has some exceptions. Here in this case, although Al of Group-13 is not a metal of Group 1 and 2, it commits itself to ionic bonding. Other elements do not show this tendency to donate or accept electrons as they have too many electrons at their outermost energy level. As a result, they do not create ionic bonding. As ionic bonding takes place through electrostatic force, it is very strong.", "figures": [ { "caption": "Formation of sodium chloride", "reference": "Fig 5.06" }, { "caption": "Formation of Magnesium oxide", "reference": "Fig 5.07" } ] }, { "section": "5.11 Covalent Bond", "text": "You have just learned how a metal atom and a non-metal atom commit to ionic bonding in order to form compounds. But what happens when you try to form a chemical bond between two non-metal atoms? In case of non-metals, losing or gaining electrons is not easy. So it might seem difficult to form a bond. However, it reality they can and do form bonds. For example when two chlorine atoms are kept close, they bond chemically together into a chlorine molecule. But how is it possible for each of them to have 7 electrons at their outermost energy level?\n\nThe electronic configuration of Chlorine is Cl(17) → 1s2 2s2 2p6 3s2 3p5\n\nSince Cl has 7 electrons at its outermost energy level, chlorine will tend to receive an electron instead of donating. But in the absence of a donor atom, the receiving will not happen also. Therefore, when two chlorine atoms come closer, 1 electron from the outermost energy level of each atom comes together as a pair and the pair of electrons positions itself in between the two nucleuses of the two atoms. This is known as electron sharing. Thus, both the atoms receive 8 electrons and assume the electronic configuration of inert gas at their outermost energy level. The result is that the two nucleuses of chlorine cannot leave each other which means they remain in a bonding. This kind of bonding is called covalent bonding. Therefore, it can be said, in a chemical bonding of two non-metal atoms, the atoms create a pair of electrons by sharing one each from their outermost energy level. Both of the atoms continue to share the pair together in a bond which is called a covalent bond. The compounds that are endowed with covalent bonds are called covalent compounds. In each covalent bonding, two electrons participate. The covalent bonding is denoted by a line (-) and the electrons are denoted by dot (.) or cross (×) marks.\n\nA chlorine molecule has two chlorine atoms and its formula is Cl2. Many non-metals remain as molecules, like hydrogen (H2), oxygen (O2), nitrogen (N2), sulfur (S8), phosphorus (P4), bromine (Br2), Iodine (I2), fluorine (F2) etc.", "subsections": [ { "title": "Covalent Bond in H2 Molecule", "text": "The electronic configuration of hydrogen is H(1) → 1s1. When 2 H atoms come close, both of them share one electron from their outermost energy level each. That means, they create a pair of electrons which makes the configuration same as inert gases. This creates a (H-H) covalent bond.", "figures": [ { "caption": "Formation of covalent bond in Hydrogen molecule", "reference": "Fig 5.08" } ] }, { "title": "Covalent Bond in O2 Molecule", "text": "The electronic configuration of oxygen is O(8) → 1s2 2s2 2p4. It lacks two electrons in its outermost energy level than that of inert gas. When two O atoms come close, both of them share two electrons from their outermost energy level each. That is, it forms 8 electrons in the last energy level. That means, they create two pairs of electrons which makes the configuration same as inert gases. This creates a (O=O) covalent bond. Here the number of covalent bond is two.", "figures": [ { "caption": "Formation of covalent bond in Oxygen molecule", "reference": "Fig 5.09" } ] } ], "text": "Covalent bond is also available in compound's molecule made of more than one non-metallic element. For example, in water's molecule, O atoms share one of their electrons from the outermost energy level with one electron of each H atom. Thus two (O-H) covalent bonds are created and water's molecule is structured.\n\nIn the H2O molecule, two pairs or 4 electrons of O atom do not participate in any bonding. However, if required, they can also create bonds which you will learn in higher classes.\n\nAn O atom is capable of forming in both ionic and covalent bonds. A Na atom, however, is never able to form in covalent bonding; it always participates in ionic bonding only. An O atom can accept 2 electrons from other element in an ionic bond or it can share 2 electrons with another element in a covalent bond. Na atom, on the other hand is capable of only donating electrons to other elements in an ionic bond. But it never shares electrons with other atoms to form a covalent bond.\n\nMolecules of elements with covalent bonds (N2, O2, Cl2, Br2, I2 etc.) are called covalent molecules and compounds with covalent bonds (CH4, CO2, HCl, NH3 etc.) are called covalent compound molecules. Many covalent molecules (CO2, NH3, O2, Cl2) remain in gaseous state at normal temperature and pressure. Some of them remain in the liquid state (H2O, C2H5OH etc.) in the same situation while some others (C10H8, S8, I2) are found in solid state. When two covalent molecules come close, a weak attraction force remains effective among them. This force is called Vander Wall's attraction force. The covalent molecules remain attached with each other due to this attractive force. That's why, it is easy to alienate them with a bit of force. Melting and boiling points of these molecules are also low. Again, Vander Wall's attraction force is hardly effective on gaseous covalent molecules. They remain as gaseous single molecules due to this.", "figures": [ { "caption": "Two (O-H) covalent bonds in water molecule", "reference": "Fig 5.10" } ] }, { "section": "5.12 Characteristics of Ionic and Covalent Bonds", "subsections": [ { "title": "(a) Melting Point and Boiling Point", "text": "The compound consisting of an ionic bond is called an ionic compound and the compound consisting of covalent bonds is called a covalent compound. The melting and boiling points of ionic compounds are higher than those of covalent compounds. Ionic compounds contain positive and negative charges which remain tightly connected with each other. Many such positive and negative charges are organized in an ionic compound in a three dimensional way to create a crystal. This results in a higher inter atomic force among them and that makes it tough to alienate from each other. Therefore, they require higher amount of heat energy to melt or to boil. Their melting and boiling point is very high. Inter atomic force in covalent compounds is comparatively weaker as it is constituted because of Vander Wall's force. Therefore, they can be boiled or melted with a lower amount of heat energy. You will see the same phenomenon with ionic compounds like NaCl, CuSO4, NaNO3, KCl, CaCl2, etc. and covalent compounds like glucose, sugar, or even water. All the experiments will prove that the boiling point and melting point of ionic compounds are higher than those of covalent compounds." }, { "title": "(b) Solubility", "text": "Take some water in a beaker or a glass jar. Add some NaCl, an ionic compound and continue to stir it. Then, do the same thing with washing soda (Na2CO3.10H2O), Copper Sulfate (CuSO4.5H2O) or some other ionic compounds; you will find them all soluble in water. However, you will not find the same result with silver chloride. That means apart from a few exceptions, ionic compounds are soluble in water. Try the same experiment with covalent compounds like naphthalene, mustard oil, kerosene etc. covalent compounds. You will find none of them soluble in water. Although there are few exceptions like sugar, glucose etc, most covalent compounds are not soluble in water.\n\nWhy are only some covalent compounds soluble in water? The reason lies in the bond structure of water. Water is a covalent compound itself where two hydrogen atoms are connected with one oxygen atom by electron sharing. But since oxygen is more electronegative than hydrogen, the two electrons of the covalent bond of water move towards oxygen a bit. As a result, oxygen atom becomes a partially negative charge while hydrogen becomes a partially positive charge, meaning a partial positive and a partial negative end is created in water molecule. This kind of charged covalent compound is called polar covalent compound. So, water is a polar soluble. Remember, the attraction force of an atom when it tries to attract the electron pair of a covalent bonding to itself is called the electronegativity of an atom. The figure 5.10 uses δ+ (delta plus) and δ- (delta minus) to express positive and negative charges.\n\nWhen the ionic compound is added to water, the polar solvent, the positively charged end of the water molecule's cation attracts the negatively charged part (anion) of the ionic compound. The same action takes place between the anion of water molecule and cation of ionic compound's molecule. When this attraction force becomes greater than that between the cation and anion of the ionic compound, then cation and anion become alienated from each other and become surrounded by water molecule. Thus ionic compound is dissolved into water. NaCl is an ionic compound and being so, it gets dissolved in the polar solvent, water (H2O). Methanol (CH3OH) is a polar compound and so it gets dissolved in polar solvent, water. Since methane (CH4) is neither an ionic compound nor a polar compound, it does not get dissolved in water.\n\nOn the other hand, there is no cation and anion in covalent compounds. They do not become attracted or distracted by cation and anion of water. As a result, they do not break down as ions in water, meaning they do not get dissolved.\n\nHowever, there are some covalent compounds that do have partially positive and partially negative ends- in other words, they exhibit polarity. For example, Ethanol (C2H5OH) is a polar compound and it get dissolved in water.", "figures": [ { "caption": "δ+ and δ- indicate partial positive and partial negative charge", "reference": "Fig 5.11" } ] }, { "title": "(c) Electrical Conductivity", "text": "Take some water solution of edible salt (NaCl) in a beaker and some water solution of sugar in another. Now put two graphite rods or any other kind of metallic rod as electrodes into each solution and finally connect battery and bulb to each of them to complete the circuit as shown in the figure 5.12. You will see, the bulb in salt water solution is lit up while the one with sugar-water solution is not. That shows the salt water solution is able to conduct electricity while sugar water cannot.\n\nYou may conclude that ionic compounds in solution with water can conduct electricity while covalent compounds cannot. But what is the reason?\n\nYou can also guess the reason very well. Electro-conductivity requires alienated positive and negative ions. In the salt water solution, Na+ and Cl- act as positive and negative ions respectively and conduct electricity. As in water solution, ionic compounds remain as alienated cations and anions, therefore, all water solutions with ionic compounds are electro-conductive.\n\nOn the other hand, covalent compounds do not conduct electricity in water solution as they do not carry alienated ions.\n\nIn CaCl2 solution, there is Ca2+ and Cl-. HCl solution contains H+ and Cl-. Therefore, they can conduct electricity. Glucose (C6H12O6) does not carry any alienated ion, so it does not conduct electricity.", "figures": [ { "caption": "Electrical conductivity of water solution of edible salt (NaCl)", "reference": "Fig 5.12" } ] }, { "title": "Formation of Crystals", "text": "Each group will take two beakers. One beaker will have salt (NaCl) and another, sugar (C12H22O11). Add water to both and heat them a bit to dissolve as much salt and sugar as possible. Now preserve both beakers for some days along with a cotton liner hanging inside each. After some days, pick up the liners- you will find salt and sugar crystals have formed around them. Usually, all ionic compounds remain as crystals. On the other hand, though some covalent compounds like sugar can form crystals. Usually, most covalent compounds are not available in crystal form.", "figures": [ { "caption": "Crystals of salt and sugar", "reference": "Fig 5.13" } ] } ] }, { "section": "5.13 Metallic Bond", "text": "We have seen that, a metal and a non metal element creates an ionic bond among themselves while two non-metal elements create a covalent bond among themselves. But when two metallic elements come closer together, there is created a metallic bond. It means, the attraction force that keeps the atoms in a piece of metal interconnected is called the metallic bond. You have obviously seen copper wire, knife, scissors, cleavers, window grill, alluminium made windows or gold ornaments etc. In all of these, numerous atoms of the same element are interconnected by means of metallic bonds inside.\n\nThe outermost energy level of each metallic atom usually contains 1, 2 or 3 electrons in its electronic configuration. Since their size is bigger than the non-metallic elements of the same period, the attractive force of the nucleus on them is less strong. As a result, metal atoms donate one or more electrons from their outermost energy level and turn into a positive ion. This positive ion is called the atomic core. These atomic cores are organized in three dimensional pattern in a metallic crystal lattice.\n\nIn the metal lattice, the donated electrons come out of the orbit and move freely at the center of the atomic core. Such electrons are called Delocalized Electrons. These electrons do not belong to any particular atom. Instead, they are shared by all the metal ions in the entire metallic structure. It can be said that the ions remain organized like a lattice in the sea of electrons. When a delocalized electron is situated amidst two metallic ions, both the ions are attracted towards the electron with an electrostatic force. This causes the two ions to remain connected, which is the basic reason of a metallic bond. These delocalized electrons are responsible for the conductivity of heat and electricity. Similarly, they are the reasons for the flexibility, brightness, and charge-resistance etc. features of a metal.", "figures": [ { "caption": "Metallic bonds", "reference": "Fig 5.14" } ], "subsections": [ { "title": "Electro Conductivity of Metals", "text": "All metals are good conductors of electricity. The delocalized electrons in the metal lattice are the carrier of electricity in them. If we connect the two ends of a piece of metal to positive (+) and negative (-) edges of a battery, the electrons will rush from the negative edge to the positive edge. That means, there will be flow of electricity from positive end to negative end. Flow of delocalized electrons creates electricity. There would not have been any electricity flow in the absence of delocalized electrons.", "figures": [ { "caption": "Mechanism of electrical conductivity of metal", "reference": "Fig 5.15" } ] }, { "title": "Heat Conductivity of Metals", "text": "When you heat an end of a piece of metal, you will find that the other end is also getting warm fast. It means, metals are heat conductors too. The reason is again delocalized electrons. When heat is applied, these electrons receive energy and increase their velocity. They rush from the heated end towards the comparatively cooler end. Thus heat is conducted in a metal." } ] } ] }, { "chapter_number": 6, "title": "Concept of Mole and Chemical Counting", "start_page": 109, "end_page": 141, "content": [ { "section": "6.1 Mole", "text": "The word mole is the unit of any chemical measurement. Suppose,\n\n12 nos of O2 = 1 dozen of O2\n100 nos of O2 = 1 hundred of O2\n1000 nos of O2 = 1 thousand of O2\n\nSimilarly, 6.023×10^23 nos O2 = 1 mole O2\n\n1 mole atom contains 6.023×10^23 atoms\n1 mole molecule contains 6.023×10^23 molecules\n1 mole ion contains 6.023×10^23 ions\n\nTherefore, the number 6.023×10^23 is used in the case with atoms, molecules and ions etc. This number is called the Avogadro number.\n\nThe quantity of a chemical substance that contains the Avogadro number (6.023×10^23) of molecules, atoms or ions is called the mole of that substance. For example, 12 grams of C contains 6.023×10^23 number of C atoms.\n\nWhen the atomic mass of atoms and the molecular mass of molecules expressed into gram unit is called one mole of a chemical substance.\n\nTherefore,\n\n12 grams of C = 1 mole C atom. Again, 18 grams of H2O contains 6.023×10^23 number of H2O molecules. Therefore,\n\n18 grams of H2O = 1 mole H2O", "subsections": [ { "title": "How to Calculate the Molecular Mass of a Molecule", "text": "The summation of atomic masses of all atoms that constitute a molecule denotes the molecular mass of the molecule. Cl2 molecule, for example, has two Cl atoms.\n\nTherefore, the molecular mass of Cl2 = atomic mass of Cl × 2 = 2×35.5 = 71\n\nThus, one mole Cl2 = 71 g Cl2.\n\nA NaCl molecule has 1 Na atom and 1 Cl atom. Therefore, the molecular mass of NaCl = atomic mass of Na + atomic mass of Cl = 23 + 35.5 = 58.5\n\nOne mole of NaCl = 58.5 g NaCl\n\nCuSO4.5H2O contains 01 Cu, 01 S, 09 O and 10 H atoms. Therefore, the molecular mass of CuSO4.5H2O = atomic mass of Cu × 1 + atomic mass of S × 1 + atomic mass of O × 9 + atomic mass of H × 10\n\n= 1×63.5 + 1×32 + 9×16 + 10×1\n= 249.5\n\nA mole of CuSO4.5H2O = 249.5 g CuSO4.5H2O" }, { "title": "Examples", "text": "Problem: What is the mass of 1 H2O molecule?\n\nSolution: We know, 1 mole H2O = 18 g H2O = 6.023 × 10^23 no of H2O molecule\n\nHere, the molecular mass of 6.023 × 10^23 H2O molecules = 18 g\n\nTherefore, the mass of 1 H2O molecule = 18 / (6.023 × 10^23) g = 2.99 × 10^-23 g\n\nProblem: How many H2SO4 molecules are there in 1 g H2SO4?\n\nSolution: We know, 1 mole H2SO4 = 98 g H2SO4 = 6.023 × 10^23 no of H2SO4 molecule\n\nHere, 98 g H2SO4 = 6.023 × 10^23 no of H2SO4 molecules\n\nTherefore, the mass of 1 g H2SO4 = 6.023 × 10^23 / 98 = 6.14 × 10^21 H2SO4 molecules.\n\nProblem: Calculate the mole of H2O present in 5 g H2O.\n\nSolution: We know, 1 mole H2O = 18 g H2O = 6.023 × 10^23 no of H2O molecules.\n\nHere, 18 g H2O = 1 mole H2O\n\n1 g H2O = 1/18 mole H2O\n\nTherefore, 5 g H2O = (1 × 5)/18 = 0.277 mole H2O." } ] }, { "section": "6.1.1 Molar Volume of Gas", "text": "The volume that 1 mole of a gaseous substance occupies is called the molar volume of that gas. 0°C temperature and 1 atm pressure together is called the standard temperature and pressure or the standard condition. The volume of 1 mole gas in this standard condition is 22.4 liter.\n\nIf n = mole number\nw = mass in gram\nV = Volume in liter\nN = Number of molecules\nM = Molecular mass\n\nThen, n = w/M\nOr, n = V/22.4\nOr, n = N / (6.023×10^23)", "examples": [ { "problem": "How many molecules are there in 1 liter CO2 gas at standard temperature and pressure?", "solution": "1 mole CO2 = 44 g CO2 = 6.023 × 10^23 no CO2 molecules = 22.4 liter CO2 gas at standard temperature and pressure\n\nAt standard temperature and pressure 22.4 liter CO2 gas contains = 6.023 × 10^23 no CO2 molecules\n\nTherefore, 1 liter CO2 gas contains = 6.023 × 10^23 / 22.4 = 2.69 × 10^22 molecules" }, { "problem": "What is the volume of 5 mole CO2 gas at standard temperature and pressure?", "solution": "Here, it is given, mole n = 5, we require to find out volume V = ?\n\nWe know n = V/22.4\nOr 5 = V/22.4\nTherefore V = 5 × 22.4 = 112 liter" }, { "problem": "What is the volume of 10 g Hydrogen gas at standard condition?", "solution": "Here, it is given, mass w = 10 g, molecular mass of H2, M = 2. We require to find out volume V = ?\n\nn = w/M = V/22.4\n10/2 = V/22.4\nTherefore V = 22.4 × 22.4 liter = 112 liter" } ] }, { "section": "6.1.2 Mole and Molecular Formula", "text": "There is a relation between mole and molecular formula. The quantity in gram determined when we express the molecular mass of a substance gotten from its molecular formula is called 1 mole of that substance. For example, molecular formula of water is H2O and its molecular mass is 18. Therefore 18 gram is called 1 gram molecular mass water or 1 mole water. It is clear here that, mole is also the gram molecular mass.\n\nMolecular formula provides some other information too. For example, in the case with H2O:\n\n1. H2O is water.\n2. The formula of 1 molecule water is H2O.\n3. The formula of 1 mole water is H2O.\n4. 1 molecule H2O contains 2 hydrogen atoms and an oxygen atom.\n5. 1 mole H2O molecule contains 2 mole hydrogen and 1 mole oxygen atoms.\n6. In 1 mole H2O molecule, the mass of H atom is 1×2 = 2g and the mass of O atom is 16×1 = 16g. Therefore, the total mass of 1 mole H2O molecule is 2 + 16 = 18g.\n7. In 1 mole H2O molecule, the number of H atoms are 6.023×10^23 × 2 = 1.20×10^24 and the number of O atoms are 6.023×10^23 × 1 = 6.023×10^23 and the number of H2O molecules are 6.023×10^23" }, { "section": "6.1.3 Molar Solution", "text": "Suppose a solute is dissolved in a solvent. At a fixed temperature, if one mole solute is dissolved in 1 liter solution, then that solution is called molar solution or 1 molar solution. If 2 mole solute is dissolved in 1 mole solution, that solution is called 2 molar solution.\n\nAn example can make us differentiate between solute, solvent and solution. Take about half a glass of water. Add some edible salt to the water and mix it with a spoon. You will see the salt is no more visible in the water, after a while. This mix of salt and water is a solution. Here water is the solvent and salt is the solute.\n\nLiquids such as water, acid, alcohol etc. are necessary in preparing solutions. In this chapter, we will mainly use water as the solvent. When water is used as solvent in a solution, the solution is called water or aqueous solution.\n\nSolution = Solute + Solvent\n\nYou may come across the terms Dilute Solution and Concentrated Solution frequently. 10 gram salt mixed in 250 mL water is a solution. Again, 15 gram salt mixed in 250 gram water is also a solution. The one with lesser amount of salt is a dilute solution while the other with more salt is a concentrated solution. Again, 10 gram salt is mixed in two glasses containing 250 mL and 200 mL water each. Can you tell which one is dilute and which one is concentrated? The solution containing more water is a dilute solution while the one with less water is a concentrated solution. Similarly in the laboratory, smaller amounts of solute in a fixed amount of solvent creates a dilute solution and greater amounts of solute in the same amount of solvent creates a concentrated solution. Actually, there is no specific rule to determine which is dilute and which is a concentrated solution. It is relative: If there is comparatively less solute, the solution is called dilute and if there is more solute, it is called concentrated.\n\nThe number of moles dissolved in every liter of solution at a certain temperature is called the molarity of the solution. If 2 mole solute is dissolved in a one liter solution at a fixed temperature, then the molarity of that solution is 2. When there is 0.5 mole solute in 1 liter solution, that is a semi-molar solution and when that same 1 liter solution has 0.1 mole solute, that is called a decimal solution. The molarity of a decimal solution is 0.1 while 0.5 is the molarity of a semimolar solution.", "subsections": [ { "title": "Preparation of Solutions with Different Molarities", "text": "There is necessity of preparing molar, semimolar and decimal solutions in the laboratory. It can be done easily following various steps. Firstly, you need to select a volumetric flask. Secondly, you need to weigh the substance that you are interested to prepare the solution of and put it in the flask. Thirdly, you need to add some water and shake the flask to prepare the solution. Then, you need to fill water to a certain mark in the flask. There is relationship in between molarity of solution, volume of solution, mass and molecular mass of the solute.\n\nMass of solute in gram unit = (molarity of solution × volume of solution in milliliter unit × molecular mass) / 1000\n\nHere, if we take Mass of solute in gram unit = w\nMolarity of solution = S\nvolume of solution in milliliter unit = V\nmolecular mass of solute = M\n\nThen w = SVM/1000\n\nTo solve the molarity related problem, we can use the above equation" }, { "title": "Example", "text": "Problem: How will you prepare 0.2 molar NaCl solution in a volumetric flask of 250 mL?\n\nSolution: Given, a volume of solution V = 250 mL, molarity of solution S = 0.2 molar, molecular mass of NaCl = 23 + 35.5 = 58.5\n\nTherefore, 1 mole NaCl = 58.5g\n\n0.2 molar NaCl solution in 1 liter or 1000 mL requires 58.5 × 0.2 = 11.7g\n\n250 mL solution requires = 11.7 × 250 / 1000 = 2.925g\n\nAdd 2.925 gram NaCl in a 250 mL volumetric flask. Pour 250 mL water inside the flask. That will complete the preparation of 0.2 molar solution.\n\nAlternative Solution: We know, w = SVM/1000\n\nTherefore, w = (0.2 × 250 × 58.5) / 1000 = 2.925g\n\nNow, follow the procedure of adding the solute and solvent to complete the preparation.\n\nProblem: How much Na2CO3 is there in a 2 liter 0.1 molar Na2CO3 solution?\n\nSolution: Molecular mass of Na2CO3 = 23×2 + 12 + 16×3 = 106\n\nTherefore, the amount of Na2CO3 necessary in a 1 liter 1 molar solution = 106g\n\nthe amount of Na2CO3 necessary in a 1 liter 0.1 molar solution = 10.6g\n\nthe amount of Na2CO3 necessary in a 2 liter 0.1 molar solution = 10.6 × 2g = 21.2g\n\nProblem: What is the molarity of the solution when there is 20 g Na2CO3 in 250 mL solution?\n\nSolution: Molecular mass of Na2CO3 = 23×2 + 12 + 16×3 = 106\n1 molarity in 1 liter solution requires 106 gram\n1 molarity in 250 mL solution requires 106 × 250 / 1000 = 26.5 gram\n26.5 g Na2CO3 in 250 mL makes the molarity 1 molar\n1 g Na2CO3 in 250 mL makes the molarity 1/26.5 molar\n20 g Na2CO3 in 250 mL makes the molarity (1 × 20) / 26.5 = 0.75 molar\n\nProblem: What is the volume of the solution in mililiter when 20 g Na2CO3 is dissolved in 0.75 molar Na2CO3 solution?\n\nSolution: Given here, S = 0.75 molar, w = 20 g, M = 23×2 + 12 + 16×3 = 106, V = ?\n\nWe know, w = SVM/1000\n20 = (0.75 × V × 106) / 1000\nV = (1000 × 20) / (0.75 × 106) = 250 mL\n\nProblem: A 250 mL solution has 20 g substance dissolved in it and its molarity is 0.75. What is the molecular mass of the solute in the solution?\n\nSolution: Given here, w = 20 g, V = 250 mL, S = 0.75 molar, M = ?\n\nWe know,\n\nw = SVM/1000\n20 = (0.75 × 250 × M) / 1000\nM = (1000 × 20) / (0.75 × 250) = 106\n\nProblem: How will you prepare 200 mL semimolar Na2CO3 solution?\n\nSolution: V = 200 mL, S = 0.5 molar, M = 23×2 + 12 + 16×3 = 106\n\nWe know,\n\nw = SVM/1000\n= (0.5 × 200 × 106) / 1000 g = 10.6g\n\nNow, take 10.6 g Na2CO3 in a pot and pour 200 mL water in it. Thus we can prepare the solution." } ] }, { "section": "6.2 The Percentage Composition of Elements in Compounds", "text": "The gram measurement of an element present in a 100 gram compound is called the percentage composition of that element. The molecular formula of a compound is the source to determine the percentage composition of various elements in the compound.\n\nPercent composition of an element in a compound = (atomic mass of element × number of atoms × 100) / molecular mass of compound %\n\nExample: The percent composition of H and Cl in HCl is shown below:\n\nMolecular mass of HCl = 1 + 35.5 = 36.5\n\nIn 36.5 gram HCl the amount of H = 1 gram\n\nIn 1 gram HCl the amount of H = 1/36.5 gram\n\nIn 100 gram HCl the amount of H = (1 × 100)/36.5 = 2.74 gram\n\nSo, the percent composition of H in HCl is 2.74%\n\nAgain,\n\nIn 36.5 gram HCl the amount of Cl = 35.5 gram\n\nIn 1 gram HCl the amount of Cl = 35.5/36.5 gram\n\nIn 100 gram HCl the amount of Cl = (35.5 × 100)/36.5 = 97.26 gram\n\nSo, the percent composition of Cl in HCl is 97.26%\n\nIt can also be calculated that the percent composition of Cl is (100 - 2.74) = 97.26%", "examples": [ { "problem": "Find out the percent composition of H and O in H2O.", "solution": "The mass of 1 mole H2O = 2 + 16 = 18 gram\nIn 18 gram H2O the amount of H = 2 gram\nIn 1 gram H2O the amount of H = 2/18 gram\nIn 100 gram H2O the amount of H = 2 × 100 / 18 = 11.11 gram\nSo, the percent composition of H in H2O is 11.11%\nAgain, the percent composition of O is (100 - 11.11) = 88.89%\n\nWe can determine the same percent composition applying values in the formula of percentage composition.\n\nPercent composition of an element in a compound = (atomic mass of element × number of atoms × 100) / molecular mass of compound %\n\nThe molecular mass of H2SO4 = (1×2 + 32×1 + 16×4) = 98\n\nHere, atomic mass of H is 1 and the number of H atoms is 2\n\nTherefore, the percent composition of H = (1×2×100)/98 % = 2.04%\n\nAtomic mass of S is 32 and the number of S atoms is 1\n\nTherefore, the percent composition of S = (32×1×100)/98 % = 32.65%\n\nAtomic mass of O is 16 and the number of O atoms is 4\n\nTherefore, the percent composition of O = (16×4×100)/98 % = 65.3%\n\nProblem: Find out the percent composition of aluminium, sulfur and oxygen in Al2(SO4)3\n\nSolution: The molecular mass of Al2(SO4)3 = 27×2 + (32×1 + 16×4)×3 = 342\n\nthe percent composition of Al = (27×2×100)/342 % = 15.78%\nthe percent composition of S = (32×3×100)/342 % = 28.07%\nthe percent composition of O = (16×12×100)/342 % = 56.14%" } ] }, { "section": "6.2.1 Percent Composition and Empirical Formula", "text": "We are already familiar with the term Molecular Formula as we have learned what it is and have applied it to determine the number of atoms of elements in a molecule. The idea of an empirical formula has been introduced to express the ratio of various atoms in a molecule. For example, there are two H atoms and two O atoms in hydrogen peroxide (H2O2). As you see, the number of hydrogen and oxygen atoms in H2O2 is 2 and 2 respectively. Therefore, the ratio of the atoms in this compound is 1:1. That means, the empirical formula of H2O2 is HO. The formula that shows the ratio of the number of atoms of different elements present in a molecule is called the empirical formula. We can easily determine the empirical formula of a compound if we know the percent composition of elements in it and its relative atomic mass.", "subsections": [ { "title": "Determining of Empirical Formula from the Percent Composition", "text": "The steps required to determine the empirical formula from the percent composition are described below:\n\nStep 1: The percent composition of the elements is to be divided by its atomic mass.\n\nStep 2: Use the smallest quotient to divide the other quotients and then multiply these new quotients with the common nearest number to turn them into integers.\n\nStep 3: Apply these integers to the right of respective symbol of elements. That forms the empirical formula.\n\nStep 4: Do not write anything if the integer obtained is 1.\n\nSuppose, in a compound, the percent compositions of carbon and hydrogen are 92.31% and 7.69% respectively.\n\nFirst, let's divide the percent compositions with their atomic masses.\n\nC = 92.31/12 = 7.69\nH = 7.69/1 = 7.69\n\nNow divide the quotients with the smallest of quotients:\n\nC = 7.69/7.69 = 1\nH = 7.69/7.69 = 1\n\nNow write these values alongside the symbols of the elements and that gives you the empirical formula. Thus, the empirical formula of this compound is C1H1 = CH." }, { "title": "Example", "text": "Problem: The percent composition of elements in a compound are given as H = 2.04%, S = 32.65% and O = 65.30%. Determine the empirical formula of the compound.\n\nSolution: First, we'll divide the percent composition of the elements by their respective atomic masses:\n\nH = 2.04/1 = 2.04\nS = 32.65/32 = 1.02\nO = 65.30/16 = 4.08\n\nNow, we'll divide the quotients by the small quotient above:\n\nH = 2.04/1.02 = 2\nS = 1.02/1.02 = 1\nO = 4.08/1.02 = 4\n\nNow, we'll write the empirical formula of the compound: H2S1O4 = H2SO4\n\nProblem: There is hydrogen and oxygen in a compound whose percent compositions are 11.11% and 88.89% respectively. What is its empirical formula?\n\nSolution: First, we'll divide the percent composition of the elements by their respective atomic masses:\n\nH = 11.11/1 = 11.11\nO = 88.89/16 = 5.55\n\nNow, we'll divide the quotients by the small quotient above:\n\nH = 11.11/5.55 = 2\nO = 5.55/5.55 = 1\n\nNow, we'll write the empirical formula of the compound: H2O1 = H2O" } ] }, { "section": "6.2.2: Determining the Molecular Formula of a Compound from Percent Composition", "text": "If we want to determine the molecular formula of a compound from its percent composition, we need to determine the empirical formula first. If the total mass of the empirical formula of that compound is equal to its molecular mass then the empirical formula itself is also the molecular formula. But when the empirical formula and molecular mass of the compound varies from each other, then we need to find out how many times greater the molecular mass is from the empirical formula.\n\nIf molecular mass is n times greater than the empirical formula, then\n\nMolecular Formula = (Empirical Formula)n\nHere, n = Molecular Mass of Compound / Mass of Empirical Formula\n\nSuppose, percent composition of a compound is C = 92.31%, H = 7.69%. The molecular mass of the compound is 78. Determine its molecular formula.\n\nLet's divide the percent composition of elements with their respective atomic masses:\n\nC = 92.31/12 = 7.69\nH = 7.69/1 = 7.69\n\nNow, we'll divide the quotients by the small quotient above:\n\nC = 7.69/7.69 = 1\nH = 7.69/7.69 = 1\n\nSo, the empirical formula of the compound: C1H1 = CH\n\nSince the empirical formula is CH, the molecular formula will be (CH)n = CnHn\n\nThe mass of empirical formula of the compound stands = 12×1 + 1×1 = 13 and its molecular mass = 78\n\nn = molecular mass of compound / mass of empirical formula = 78/13 = 6\n\nThus, the molecular formula of the compound is C6H6" }, { "section": "Determining Molecular Formula from Empirical Formula", "text": "The molecular formula of a compound can be the base to determine its empirical formula. Suppose, we need to find the empirical formula of glucose (C6H12O6)\n\nA glucose (C6H12O6) molecule consists of 6C atoms, 12H atoms and 6O atoms.\n\nThe ratio of atoms C:H:O = 6:12:6 = 1:2:1\n\nTherefore, the empirical formula of glucose is C1H2O1 = CH2O\n\nSometimes, the empirical formula and molecular formula are similar. For example, the molecular formula of water is H2O, its empirical formula is H2O too. Both the formulas for sulfuric acid is H2SO4.\n\nUsually, the compounds, all the atoms of which can be divided by a certain number, have different molecular and empirical formulas. The molecular formula of benzene is C6H6. Since the number of atoms here are divisible by 6, therefore, its empirical formula will be C1H1 = CH. Similarly, the molecular formula of ethene is C2H4. Therefore, its empirical formula is C1H2 = CH2." }, { "section": "6.3 Chemical Reactions and Chemical Equations", "subsections": [ { "title": "Chemical Reactions", "text": "The change which causes a substance to get a new set of properties giving up its own properties and features is called a chemical change. The process that brings the change is called a chemical reaction. To briefly represent a chemical reaction, we use a special kind of expression. This is called a chemical equation. Chemical equations use symbols, formula and sign to represent chemical substances and the process of the reaction.\n\nThe substances that are used to begin a chemical reaction are called reactants. The substance or substances with new properties that are formed at the end of the reaction are called products.\n\nThere are some rules observed to write chemical equations in order to express chemical reactions. The rules are:\n\n1. In a chemical equation, the reactants are written on the left side and the products are written on the right side; an equal (=) sign or an arrow (→) mark is placed in the middle.\n\n2. The reactants and products are written by means of their symbols and formulas. If there are more than one reactants and products, they are written with plus sign.\n\n3. The number of atoms of different elements on the left side and the number of atoms of the same elements on the right side need to be equalized. This is called balancing of the chemical equation.\n\n2H2 + O2 → 2H2O\n\n2H2 + O2 = 2H2O\n\n4. Sometimes reactions are not balanced in the equations. In such cases, the arrow mark is used instead of the equal sign.\n\nH2 + O2 → H2O\n\n5. Sometimes, the physical states of both reactants and products are also mentioned in an equation. It is written on the right side of the element or compound in first brackets (). If the physical state of the substance is a solid, we write (s), if the state is liquid, we write (l), if gaseous, we write (g). When the substance is in the form of an aqueous solution, we write (aq). In the above reaction, the reactants are gases and the product is liquid water. So we write:\n\n2H2(g) + O2(g) → 2H2O(l)\n\nThe main objective of a chemical equation is to express which elements have participated in the reaction to form which product. That is why, it is not always necessary to balance a chemical equation.\n\n6. However, if an equation is to show how much heat has been produced or absorbed in a reaction, it has to be balanced and the physical states of reactants and products are to be written.\n\nSolid substance carbon reacts with oxygen gas and produces carbon dioxide CO2 gas. The equation will be as shown below:\n\nC(s) + O2(g) → CO2(g)\n\nSolid calcium carbonate reacts with aqueous solution of hydrochloric acid to produce calcium chloride, gaseous carbon di oxide and liquid water.\n\nCaCO3(s) + HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l)\n\ncalcium carbonate hydrochloric acid calcium chloride carbon dioxide water\n\nSome reactions are there that require heat to be applied. The heat is expressed with a delta (Δ) sign above the arrow mark. For example, if heat is applied to solid magnesium nitrate, it produces magnesium oxide, nitrogen dioxide gas and oxygen gas.\n\n2Mg(NO3)2(s) → 2MgO(s) + 4NO2(g) + O2(g)" } ] }, { "section": "6.3.1 Balancing Chemical Equations", "text": "Chemical reactions are briefly expressed through chemical equations. Since chemical reactions follow the law of conservation of mass, the number of atoms of each element present in the reactants must be equal to the number of atoms of those elements in the products. When both the left side (the reactants) and right side (the products) of an equation has the same number of atoms of the same elements, we call that a balanced equation. See the example below:\n\nMg + HCl → MgCl2 + H2\n\nIt is true that we get magnesium chloride and hydrogen when magnesium and hydrochloric acid react; therefore, the reaction is okay. However, the equation is not balanced as the number of hydrogen and chlorine atoms on both sides are not equal. Therefore, this equation is not yet balanced.", "subsections": [ { "title": "The Process of Balancing Equations", "text": "To make the number of atoms of different elements equal, the formula of reactants and products are multiplied by suitable numbers (1, 2, 3, 4 ....). There is no specific rule to balance equations, but some strategies are followed in this regard. They are:\n\n1. The equation is written using the correct formula of reactants and products.\n\n2. If the reactants and products are compound substances, that is, if the atoms of more than one element are present in the formula, balance the equation, multiplying the reactants or products or both with the required numbers.\n\n3. First the number of atoms present in the molecules of compound substances are balanced. Then come the number of atoms of elements.\n\n4. When the number of atoms of each and every element present in the reaction on both the sides are equal, then the balancing of the equation is done.\n\nLet us examine some examples in this regard.\n\nExample 1: Mg + HCl → MgCl2 + H2\n\nIn the above reaction, the number of Cl atom in the compound HCl on the left is one while in the compound MgCl2 there are two Cl atoms. It is understood that the number of Cl on both sides are not equal. The same way, on the left, there is one H atom while on the right, there are two H atoms. H atoms are also not balanced. Mg atom on both sides are equal as there is only one on each side.\n\nFirst, let us balance the Cl atom. For this, let us multiply HCl on the left side with 2:\n\nMg + 2HCl → MgCl2 + H2\n\nNow, a brief check will tell us that all atoms of various elements present on both the sides of the equation are equal. Therefore, the balancing of the equation is done. When the balancing of the equation is done, it can be written with equal (=) sign too.\n\nMg + 2HCl = MgCl2 + H2\n\nExample 2: Na2CO3 + HCl → NaCl + H2O + CO2\n\nThis is not a balanced equation as the left side has two Na while the right has one. Therefore, we multiply NaCl with 2:\n\nNa2CO3 + HCl → 2NaCl + H2O + CO2\n\nStill it is not balanced. Now the right has two Cl while the left has one Cl. Multiply HCl on the left with 2:\n\nNa2CO3 + 2HCl → 2NaCl + H2O + CO2\n\nNow, number of atoms of every element on both sides are equal.\n\nNa2CO3 + 2HCl = 2NaCl + H2O + CO2\n\nExample 3: Aluminum oxide reacts with hydrochloric acid and produces aluminium chloride and water.\n\nAl2O3 + HCl → AlCl3 + H2O\n\nTo strike a balance of Al on both sides, let us multiply AlCl3 with 2\n\nAl2O3 + HCl → 2AlCl3 + H2O\n\nTo balance the number of Cl, multiply HCl on the left with 6:\n\nAl2O3 + 6HCl → 2AlCl3 + H2O\n\nStill balance is lacking as the number of O on the left is 3 while on the right is 1. There is a difference between the numbers of H too. So, let us multiply H2O with 3:\n\nAl2O3 + 6HCl → 2AlCl3 + 3H2O\n\nNow, there is balance.\n\nAl2O3 + 6HCl = 2AlCl3 + 3H2O" } ] }, { "section": "6.3.2 Mole and Chemical Equation", "text": "Certain amounts of a reactant reacts with a certain amount of another reactant and produces a certain amount of product or products. The branch of chemistry that deals with measurements of products from amounts of reactants and measurements of reactants from amounts of products is called Stoichiometry. The information that can be gathered regarding mole from a chemical equation is the Stoichiometry of that reaction.\n\nAnalyzing the Stoichiometry, we can tell how many reactants reacted to produce how many products, how many moles of reactants formed how many moles of products, how many grams of reactants participated in the reaction to produce how many grams of products.\n\nAccording to stoichiometry, we can write\n\nThese accounts presented below a balanced equation of a chemical reaction are called its Stoichiometry. When both reactants and products are gaseous substances, in the Stoichiometry, under standard conditions, 1 mole gaseous substance has the volume of 22.4 liter.", "examples": [ { "problem": "How much oxygen is necessary for 5 gram magnesium to react and produce magnesium oxide completely?", "solution": "Magnesium reacts with oxygen and produces magnesium oxide. The balanced equation of this reaction along with its Stoichiometry is shown above. Accordingly with this Stoichiometry:\n\n48 gram magnesium reacts with 32 gram oxygen\n1 gram magnesium reacts with (1×32)/48 gram oxygen\n5 gram magnesium reacts with (1×32×5)/48 = 3.33 gram oxygen" }, { "problem": "How many grams of magnesium oxide will be produced if we put the necessary amount of oxygen with 2 gram magnesium metal?", "solution": "According to the Stoichiometry of the reaction:\n\n48 gram Mg metal produces 80 gram magnesium oxide\n1 gram Mg metal produces 80/48 gram magnesium oxide\n2 gram Mg metal produces (2×80)/48 = 3.33 gram magnesium oxide" }, { "problem": "How much oxygen is necessary alongside the required amount of magnesium metal to produce 10 gram magnesium oxide?", "solution": "According to the Stoichiometry of the reaction:\n\n80 gram magnesium oxide is produced from 32 gram oxygen\n1 gram magnesium oxide is produced from 32/80 gram oxygen\n10 gram magnesium oxide is produced from (32×10)/80 = 4 gram oxygen" }, { "problem": "How many NH3 molecules will be produced from 5 N2 molecules?", "solution": "N2(g) + 3H2(g) → 2NH3(g)\n\nFrom the equation:\n\n6.023×10^23 no of molecules of N2 produces 2×6.023×10^23 no of molecules of NH3\n1 no of molecules of N2 produces (2×6.023×10^23)/(6.023×10^23) = 2 no of molecules of NH3\nSo, 5 no of molecules of N2 produces 2 × 5 = 10 no of molecules of NH3" } ] }, { "section": "6.4 Limiting Reactant", "text": "In a chemical reaction, the substances that participate in the reaction are called reactants, and the substances that are formed as a result are called products. Among multiple reactants, the reactant whose amount is less than the stoichiometric amount is called the limiting reactant. The amount of a limiting reactant will tell us how much of which reactant will react in the reaction, how much residue will be left and how much of which product will be produced.", "figures": [ { "caption": "Here magnesium metal is the limiting reactant", "reference": "Fig 6.02" } ], "examples": [ { "problem": "4 oxygen molecules are put into 4 atoms of magnesium metal. Which is the limiting reactant here?", "solution": "2Mg + O2 → 2MgO\n\n2×6.023×10^23 no of atoms 6.023×10^23 no of molecules 2×6.023×10^23 no of molecules\n\nThe above equation tells us that, 1 O2 molecule is necessary to react with 2 metallic atoms of Mg. So, 2 O2 molecules are necessary to complete the reaction with the given 4 Mg atoms. That means, (4 - 2) = 2 molecules of oxygen will be left over when all the given magnesium atoms will finish themselves in the reaction. Here the magnesium atoms do not remain anymore at the end of the reaction. Therefore, the magnesium is the limiting reactant in this reaction.\n\nWhat would have happened if 30 molecules of oxygen were mixed with 70 atoms of magnesium metal?\n\nSince one O2 molecule reacts with 2 Mg atoms, 70 Mg atoms would require (70 ÷ 2) = 35 O2 molecules to finish themselves in the reaction. But the given number of O2 is only 30. Therefore, oxygen will finish itself in the reaction and it is the limiting reactant here." }, { "problem": "75 g chlorine gas is mixed with 5 g hydrogen gas. Which is the limiting reactant here? How much of which reactant will be left over at the end of the reaction?", "solution": "The equation of the reaction tells:\n\n2 gram hydrogen gas needs 71 gram chlorine in the reaction\nSo, 5 gram hydrogen gas needs in the reaction (71×5)/2 = 177.5 gram chlorine\n\nSince only 75 gram chlorine is given for the reaction, so Cl2 will finish itself earlier and it is the limiting reactant." } ] }, { "section": "6.5 Calculation of the Percentage of Yield", "text": "The reactants used in chemical reactions are not always found as 100% pure. The purest chemical substances / reactants are called Analar or Analar grade substance. Analar substances are 99% pure. The impure substances are purified through crystallization, distillation, fractional distillation, chromatography etc processes which you will learn about in higher classes.\n\nMany a times, one or more purification process fails to yield 100% pure products. When the reactant is not 100% pure, the reaction does not yield the amount of product that was calculated from the amount of limiting reactant.\n\nThe amount of product from a chemical reaction, in percentage, can be determined following the formula below:\n\nPercentage of yield = (Amount of Product Obtained from Reaction × 100) / Calculated Amount of Product from Reaction", "examples": [ { "problem": "2 gram metallic magnesium reacts with the necessary amount of oxygen to yield 3.25 gram magnesium oxide. What is the percentage of the yield?", "solution": "2Mg(s) + O2(g) → 2MgO(s)\n2×24 = 48g 1×32 = 32g 2×40 = 80g\n\nAccording to the equation:\n\n48 gram magnesium yields 80 gram MgO\nSo, 2 gram magnesium yields (2 × 80) / 48 = 3.33 gram MgO\n\nThe actual yield after the reaction is 3.25 gram magnesium oxide.\n\nTherefore, percentage of the yield = (3.25 × 100) / 3.33 = 97.6%" } ] }, { "section": "Experiment", "text": "Name of Experiment: Preparation of 0.1 molar sodium carbonate solution in a 250 mL volumetric flask.\n\nPrinciple: Sodium carbonate (Na2CO3) is a primary standard substance because it is found in pure and dry state, it can be directly weighed on a balance, its molar solution is long lasting. To prepare 0.1 molar sodium carbonate solution in a volumetric flask, the following calculation is necessary:\n\nHere, V = 250 mL, S = 0.1 molar, M = 23×2 + 12 + 16×3 = 106\nw = SVM/1000\nw = (0.1 × 250 × 106) / 1000 gram\nw = 2.65 gram\n\nIf we weigh and put 2.65 grams of Na2CO3 inside a volumetric flask and fill the flask with 250 mL water, the 0.1 molar sodium carbonate solution will be prepared. However, this molar solution preparation is very tough as to weigh 2.65 gram sodium carbonate is really tough. Therefore, the solution is made at a nearer molarity.\n\nNecessary Instruments: 250 mL volumetric flask, funnel, weighing bottle, chemical balance, wash bottle.\n\nChemicals: Pure sodium carbonate, water\n\nProcedure\n\n1. A funnel is inserted in the mouth of a clean 250 mL volumetric flask.\n2. A dry weighing bottle is weighed on the chemical balance.\n3. Now, pour some sodium carbonate into the weighing bottle in a way so that the total weight of the bottle is 2.65 gram higher than the previous weight.\n4. Pour the sodium carbonate from the weighing bottle inside the volumetric flask through the funnel.\n5. Pour the distilled water slowly from the wash bottle inside the volumetric flask. After pouring half the water, fix a cork on the mouth of the volumetric flask and shake it so that the sodium carbonate is dissolved fully into the water. Now, add the rest of the water to fill up 250 mL.\n\nCaution\n\n1. Take dry and pure sodium carbonate\n2. Ensure the weighing bottle is dry\n3. Add distilled water only", "figures": [ { "caption": "Preparation of 0.1 molar sodium carbonate solution", "reference": "Fig 6.03" } ] }, { "section": "Experiment", "text": "Determination of percent composition of lattice water of hydrated copper sulphate\n\nPrinciple: Blue vitriol's chemical name is pentahydrate copper sulphate. Its formula is CuSO4.5H2O. Blue vitriol consists of copper sulphate and 5 molecules of water. It is a blue colored crystal lattice. There are five moles water in it. If heat is applied, that water vaporizes and its colour turns into white. These five moles of water are called crystal water.\n\nCuSO4.5H2O → CuSO4 + 5H2O\n\nIngredients: Copper sulphate, desiccators, chemical balance, ceramic bowl, tripod stand, net, Bunsen burner/spirit lamp\n\nProcedure\n\n1. Weigh the porcelain bowl on the balance. Suppose, the weight is a gram. Now take some copper sulphate in the bowl and weigh it again. Let's say, the weight now is b gram. Therefore, the mass of copper sulphate is (b-a) gram.\n\n2. Fix the net on a tripod stand and put the bowl containing copper sulphate on it. Heat it with a Bunsen burner or spirit lamp.\n\n3. Keep marking the copper sulphate as heat is applied. The blue colour will gradually turn white. Since the water in the blue vitriol is vaporizing, it is transforming its colour.\n\n4. When the transformation of colour is complete, stop the heating.\n\n5. Swiftly take the bowl to the desiccators and weigh it again after cooling. If it isn't done fast, the copper sulphate will again absorb water and turn blue. Let's assume, this new weight is c.\n\nThat mean, after the vaporization of water, copper sulphate's mass is (c-a) gram. The mass of vaporized water from the blue vitriol is (b-a) - (c-a) gram = (b-c) gram\n\nCalculation\n\nMass of removed water from (b-a) gram copper sulphate = (b-c) gram\n\nSo, mass of removed water from 100 gram copper sulphate = ((b-c)/(b-a)) × 100 gram\nThe percent composition of crystallized water in copper sulphate is ((b-c)/(b-a)) × 100%\n\nCaution\n\nThe heating has to be slow and careful so that the heat reaches all the spots. After the removal of water, the weighing has to be quick.", "figures": [ { "caption": "Determination of lattice water in blue vitriol", "reference": "Fig 6.04" } ] } ] }, { "chapter_number": 7, "title": "Chemical Reactions", "start_page": 142, "end_page": 167, "content": [ { "section": "7.1 Changes of Matter", "text": "The substances existing in nature undergo changes due to heat, pressure and contact with other substances. There are two types of changes: physical change and chemical change.", "subsections": [ { "title": "7.1.1 Physical Change", "text": "Every chemical substance consists of one or more elements. Sometimes, changes occur only in physical conditions of a substance leaving their chemical structure unchanged. This is called a physical change. For example, if a solid piece of ice, is kept at room temperature, it absorbs heat from the environment and gradually melts into liquid water. Again, when liquid water is heated to 100°C, it turns into water vapor. Here, the molecular formula of all three- water, ice and vapor is the same H2O. That means each molecule of them has the same two hydrogen and one oxygen atoms in them. Therefore, all three substances are the same, only their physical states are different- ice is solid while water is liquid and vapor is gaseous. This kind of change is called a physical change." }, { "title": "7.1.2 Chemical Change", "text": "Sometimes, due to the change of external temperature or pressure and contact with some other substance, some substances change into completely new substances. This kind of change is called a chemical change. That means, the kind of change that forms new substances with a new set of properties is called a chemical change. The new substance formed through chemical change gets the same molecules that were there in the original elements. Isolated ions or atoms are formed out of the dissociation in the bond of the previous element. These isolated ions or atoms later constitute new bonds among themselves and create new molecules. As a result, chemical change also implies dissociation of old bonding and formation of new bonding too. The gas we use for cooking basically consists of methane (CH4). When methane gas is burnt in oxygen, carbon dioxide, water vapor and heat energy are produced. This is a chemical change.\n\nCH4(g) + O2(g) → CO2(g) + H2O(l)\n\nSimilarly, calcium carbonate reacts with hydrochloric acid and produces calcium chloride, carbon dioxide and water. This is also a chemical change.\n\nCaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l)" } ] }, { "section": "7.2 Classification of Chemical Reactions", "text": "We can classify the chemical reactions in the following ways:", "subsections": [ { "title": "7.2.1 Direction of Reaction", "text": "According to direction of reaction, chemical reactions are of two kinds: Irreversible reactions and Reversible reactions.\n\nIrreversible Reactions: In irreversible reactions, only the reactants convert to products. Products cannot be converted to reactants by a reaction if any one of the products from the reaction is removed from the reaction medium. For example, calcium carbonate, when heated in a container breaks into solid limestone and gaseous carbon dioxide. If the carbon dioxide gas is removed from the container, then too, the limestone will not convert back to calcium carbonate. Thus, it is an irreversible reaction. Irreversible reactions are written in equations with a right faced arrow (→) mark in the midst of reactants and products.\n\nCaCO3(s) → CaO(s) + CO2(g)\n\nReversible Reactions: In a reversible reaction, the reactants react and convert to products and the products react again and revert to reactants. In reversible reactions, two reactions continue simultaneously. In one reaction, the reactants react and produce the product, which is called a forward reaction. In the other one, the products react again and convert to the reactant, which is called a backward reaction. Reversible reactions are written in the equation with double headed half arrow marks (⇌) in the midst of reactants and products. For example, ethanol and ethanoic acid react in the presence of hydrochloric acid and produce ethyl ethanoate ester and water. Conversely, ethyl ethanoate ester and water react with each other and produce ethanol and ethanoic acid. In an equation, it can be shown as,\n\nC2H5OH + CH3COOH →(HCl) CH3COOC2H5 + H2O\n\nSimilarly, hydrogen and iodine react and produce hydrogen iodide as a product and this product again converts into hydrogen and iodine. This is also a reversible reaction.\n\nH2 + I2 ⇌ 2HI\n\nIndeed, all reactions are reversible reactions, but in some reactions, the rate of backward reaction is so small compared to forward reaction that the reaction appears to be an irreversible reaction." }, { "title": "7.2.2 Heat Change in Chemical Reactions", "text": "You have already learned that heat change is a factor in chemical reactions. Based on the absorption and generation of heat, reactions are classified into two categories: exothermic reactions and endothermic reactions.\n\nExothermic Reactions: A chemical reaction that produces heat is called an exothermic reaction. For example, in the Heber process, 1 mole of nitrogen and 3 moles of hydrogen produce 2 moles of ammonia and 92 kilojoules of heat are generated. The reaction is:\n\nN2(g) + 3H2(g) →(Fe) 2NH3(g) + 92 kJ\n\nHere, ground Fe acts as the catalyst. According to the balanced equation, the heat change during a reaction is called reaction heat. It is denoted by ΔH. If heat is evolved during a reaction, its value is negative.\n\nN2(g) + 3H2(g) →(Fe) 2NH3(g) ; ΔH = -92 kJ\n\nEndothermic Reactions: When heat is absorbed at the time of producing the products from the reactants, the reaction is called an endothermic reaction. 1 mole of nitrogen and 1 mole of oxygen react and produce 2 moles of nitric oxide. When they do so, they absorb 180 kJ heat. This is an endothermic reaction.\n\nN2(g) + O2(g) + 180 kJ → 2NO(g)\n\nHere also, we can use the symbol of heat ΔH. In endothermic reactions, the value of absorbed heat is positive.\n\nN2(g) + O2(g) → 2NO(g) ; ΔH = +180 kJ" }, { "title": "7.2.3 Electron Transfer", "text": "Depending on electron transfer, reactions can be divided into two types: redox reactions and non-redox reactions.\n\nRedox Reactions: The term redox is formed by combining the initial part of reduction, 'red' and the initial part of oxidation, 'ox'. It means redox combine both reduction and oxidation. In redox reactions, there occurs an electron transfer in the reaction. A reactant donates an electron and the other reactant receives that electron. That means, a redox reaction is divided in two parts. In one part, the donation of the electron takes place which is called oxidation half reaction. In the other half, the other reactant accepts the donated electron, which is called the reduction half reaction. The reactant which donates the electron in such a reaction is called reductant and the one which accepts the electron is called oxidant.\n\nNa + 1/2 Cl2 → NaCl\n\nHere, Na is donating an electron as it is a reductant substance and conversely, Cl is accepting that electron as it is an oxidant substance.\n\nThe reaction in which electron donation of an atom occurs or positive charge of that atom increases or negative charge of that decreases is called an oxidation reaction.\n\nFe2+ → Fe3+ + e- [oxidation reaction]\nNa0 → Na1+ + e- [oxidation reaction]\n\nThe reaction in which an atom accepts an electron or the positive charge of an atom decreases or the negative charge of an atom increases is called a reduction reaction.\n\nCl0 + e- → Cl1- [reduction reaction]\nCu2+ + e- → Cu1+ [reduction reaction]\n\nOxidation Number: Atoms in molecules or radicals sometimes tend to donate electrons and sometimes tend to accept electrons. The tendency to donate an electron of an atom is denoted by a number added with a plus (+) mark and the tendency to accept an electron of an atom is denoted by a number added with a minus (-) mark. In any molecule or radical, this number with plus or minus mark is the oxidation number.\n\nThe oxidation number of neutral atoms like Na, Mg, Fe etc. are taken to be zero (0). Similarly, atoms in molecules that consist of homogenous atoms like H2, O2, N2, Cl2, Br2 etc. are regarded to have oxidation number of zero.\n\nThe oxidation number of Fe in FeSO4 is +2 while the oxidation number of the same atom in Fe metal is 0.\n\nDetermining Oxidation Number: In a compound the oxidation number of an element depends on the oxidation numbers of other elements of the compound. To determine the oxidation number of an element in a compound, standard oxidation numbers of other elements is used.", "tables": [ { "caption": "Table 7.01: Oxidation Number of Atoms in Different Compounds", "headers": ["Rule of Oxidation Number", "Formula of Compound", "Element and Oxidation Number"], "rows": [ ["Oxidation number of metals is positive and oxidation number of nonmetals is negative.", "NaCl", "Na = +1, Cl = -1"], ["Oxidation number of a neutral or free element is zero.", "Fe, H2", "Fe = 0, H = 0"], ["Total oxidation number of atoms of a neutral compound is zero.", "H2O", "H = +1, O = -2, Total = 0"], ["Total oxidation number of atoms of a charged ion is equal to their charge.", "SO4-2, NH4", "SO4-2 = -2, NH4+ = +1"], ["In compound oxidation number of alkali metals is +1.", "KCl, K2CO3", "K = +1"], ["In compound oxidation number of alkaline earth metals is +2.", "CaO, MgSO4", "Ca = +2, Mg = +2"], ["Oxidation number of halogen in metal halide is -1.", "MgCl2, LiCl", "Cl = -1"], ["In most compounds, oxidation number of hydrogen is +1 but oxidation number of hydrogen in metal hydride is -1.", "NH3, LiAlH4", "H = +1, H = -1"], ["In most compounds (oxides), oxidation number of oxygen is -2 but oxidation number of oxygen in peroxide is -1 and oxidation number of oxygen in superoxide is -1/2 (i.e.-0.5).", "K2O, CaO, K2O2, H2O2, NaO2, KO2", "O = -2, O = -1, O = -1/2"] ] } ] } ], "text": "Oxidation- reduction is a simultaneous process: You already know what is oxidation and what is reduction and what is an oxidant and what is a reductant. Oxidation- reduction reactions takes place simultaneously. Let us consider the reaction below:\n\nNa + 1/2 Cl2 → NaCl\n\nHere, the reduction agent Na has donated one electron from its outermost shell to complete the oxidation half reaction. The oxidant Cl has accepted that electron and completed the reduction half reaction.\n\nOxidation half reaction Na0 → Na+ + e-\nReduction half reaction Cl0 + e- → Cl-\n\nIf we add these two half reactions, we get the oxidation- reduction reaction.\n\nNa0 + Cl0 → Na+ + Cl- ≡ NaCl\n\nIt is clear here that the reduction agent has donated the electron to the oxidation agent. If oxidation agent Cl would not accept the electron, the reduction agent Na would not have been able to donate the electron. So, it can be said, oxidation and reduction will occur together. They are simultaneous processes.\n\nSince the reductant donates an electron and the oxidant accepts that electron, therefore, oxidation- reduction is actually the transfer of electrons.\n\nThere are some reactions where oxidation- reduction occurs. They are:\n\n1. Addition Reaction\n2. Decomposition Reaction\n3. Substitution or Displacement Reaction\n4. Combustion Reaction\n\n1. Addition Reaction: A reaction in which a new compound is formed by the combination of two or more elements or molecules is called an addition reaction. For example, chlorine adds with ferrous chloride and produces ferric chloride:\n\n2FeCl2(aq) + Cl2(g) → FeCl3(aq)\n\nSimilarly, hydrogen gas combines with nitrogen gas and forms ammonia gas:\n\nN2 + 3H2 → 2NH3\n\nHowever, the addition reaction where two or more elements combine together to form a new compound is called synthesis. According to this definition, the reaction for ammonia gas is also a synthesis.\n\n2. Decomposition Reaction: The process in which a compound breaks into one or more elements or molecules is called a decomposition reaction. For example, when heat is applied on phosphorus pentachloride, it decomposes into phosphorus trichloride and chlorine.\n\nPCl5 →(heat) PCl3 + Cl2\n\nSimilarly, one water molecule decomposes to produce two different molecules on electrolysis. Hydrogen and oxygen are produced in cathode and anode.\n\n2H2O(l) →(electrolysis) 2H2(g) + O2(g)\n\n3. Substitution or Displacement Reaction: The process in which an element or radical displaces another element or radical from a compound and takes its place is called a substitution reaction. For example, zinc metal displaces hydrogen from sulfuric acid to form zinc sulfate and hydrogen gas:\n\nZn(s) + H2SO4(l) → ZnSO4(aq) + H2(g)\n\n4. Combustion Reaction: The process in which any compound or element is burnt in the presence of atmospheric oxygen and converted to oxides of its elements is called a combustion reaction. Usually heat is evolved in combustion reactions. This process also involves electron exchange. For example, natural gas or methane reacts with oxygen of air and produces carbon dioxide and water.\n\nCH4(g) + 2O2(g) → CO2(g) + 2H2O(g) + Heat\n\nSimilarly, S, C, Mg and H2 produce their oxides and heat evolves when they are burnt.\n\nS(s) + O2(g) → SO2(g) + Heat\nC(s) + O2(g) → CO2(g) + Heat\n2Mg(s) + O2(g) → 2MgO(g) + Heat\n2H2(g) + O2(g) → 2H2O(g) + Heat\n\nIn all combustion reactions, oxygen accepts an electron donated by the other element or compound. Therefore, this kind of a reaction belongs to the oxidation- reduction type.\n\nNon-Redox: There are some reactions where electron exchange does not occur. These reactions are called non- redox reactions. In this kind of reaction, there is no involvement of increase or decrease in oxidation number of any reactant because there is no electron exchange. Different kinds of non- redox reactions are discussed below: (1) Neutralization reaction (2) precipitation reaction etc.\n\n1. Neutralization Reaction: An acid and a base react with each other and neutralize into salt and water, in some reactions, which are known as neutralization reactions. They are also known as acid-base reactions. NaOH and HCl, for example neutralize each other and convert to NaCl salt and water:\n\nHCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)\n\nHeat always evolves from neutralization reactions. That means, neutralization reactions are exothermic. When both acid and base are strong, the evolved heat amounts to ΔH = -57.34 kJ. In this kind of a reaction, the acid provides the hydrogen ion (H+) while the base provides the hydroxide ion (OH-). These two ions then react and produce water. In NaCl solution, sodium ion is Na+ and chlorine ion is Cl-.\n\nH+ + Cl- + Na+ + OH- → Na+ + Cl- + H2O\n\nIn this solution, the two ions Na+, Cl- do not participate in the reaction. They are called spectator ions. The actual equation of a neutralization reaction is:\n\nH+ + OH- → H2O + 57.34 kJ\n\nFinally, neutralization reaction is the water producing reaction by means of H+ and OH- ions. Whatever the strength of both the acid and the base we take in this kind of reaction they will provide the same ions and produce water. The amount of heat that evolves to produce 1 mole water is called neutralization heat. Calculation tells us that it evolves 57.34 kJ heat.", "experiments": [ { "title": "Demonstration of the Neutralization Reaction", "description": "Take 10 mL NaOH solution in a beaker. Take HCl solution in another beaker. Dip a blue litmus paper in the solution. Now use your left hand to pour HCl solution with a dropper in the NaOH solution. Simultaneously use a glass tube in your right hand to stir and mix the solutions. The moment the blue litmus paper turns red, you will understand HCl has neutralized the NaOH solution.\n\nHCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)" }, { "title": "Demonstration of a Precipitation Reaction", "description": "In a test tube, take 2-3 mL ferrous sulfate solution and add NaOH solution with that in drops. You will see a green precipitate is forming gradually and settling at the bottom of the tube. The two chemical compounds are forming solid Fe(OH)2 precipitate here:\n\nFeSO4 + NaOH → Fe(OH)2↓ + Na2SO4\n\nThe precipitate compound is denoted by a bottom- faced arrow mark (↓)at its right.", "figures": [ { "caption": "Precipitation reaction", "reference": "Fig 7.02" } ] } ], "subsections": [ { "title": "2. Precipitation Reaction", "text": "When two soluble compounds are mixed in a certain solvent and if any new compound is produced that is insoluble or sparsely soluble in that solvent, the compound settles at the bottom of the container as a solid. This new solid compound at the bottom is called the precipitate. The reaction in which the produced compound settles at the bottom of the container as precipitate is called the precipitation reaction. For example, when silver nitrate (AgNO3) solution is mixed with sodium chloride (NaCl) solution, they react to produce silver chloride and sodium nitrate. NaNO3 is highly soluble in water, so it remains dissolved in the solution. But since solubility of AgCl is sparse, it settles at the bottom as precipitate:\n\nNaCl(aq) + AgNO3(aq) → AgCl(s)↓ + NaNO3(aq)\n\nWhen you add barium chloride (BaCl2) solution with sodium sulfate (Na2SO4) solution, they produce barium sulfate (BaSO4) and sodium chloride (NaCl). Barium sulfate is precipitated.\n\nNa2SO4(aq) + BaCl2(aq) → BaSO4(s)↓ + 2NaCl(aq)\n\nHowever, there are some precipitation reactions in which there occurs an electron exchange. You will know about them in higher classes." } ] }, { "section": "7.3 Special Types of Chemical Reactions", "text": "There are some chemical reactions which do not fall in the redox and non- redox classifications. Some of them are discussed below:\n\nHydrolysis Reactions: The chemical reactions, in which water as a reactant reacts with other compounds and produces some new compounds is called hydrolysis. For example:\n\nSiCl4 + H2O → Si(OH)4 + 4HCl\n\nHere, SiCl4 and H2O are participating in a reaction so it is a hydrolysis reaction. This kind of reaction sometimes produces non- transparent soluble compounds. In that case, the reaction may be considered as a precipitation reaction. The following reaction can be classified as both a hydrolysis reaction and a precipitation reaction:\n\nAlCl3(s) + 3H2O(l) → Al(OH)3(s) + 3HCl(aq)\n\nHere, Al(OH)3 is non- soluble in water.\n\nHydration Reaction: One or more molecules of water combine with ionic compounds during formation of a crystal lattice. This kind of reaction is called a hydration reaction. Water molecules that combine with ionic compounds is called lattice water or hydrated water. For example, 5 moles of water (5H2O) combines with copper sulfate (CuSO4) and produces pentahydrate copper sulfate (CuSO4.5H2O).\n\nCuSO4 + 5H2O → CuSO4.5H2O\n\nThere are many such reactions:\n\nA hydration reaction is basically similar to an addition reaction. However, in addition reactions, there is electron exchange whereas electron exchange does not occur in hydration.\n\nIsomerization Reaction: Two compounds with similar molecular formula but with different properties are called isomers of each other. A chemical reaction in which atoms in a molecule rearrange themselves to form one isomer from another isomer is called isomerization. For example, H4N2CO molecular formula denotes two compounds with varied structural formula: NH4CNO (ammonium cyanate) and urea (H2N - CO - NH2). They are isomers of each other. When heat is applied to ammonium cyanate, it produces urea.\n\nNH4CNO →(Heat) H2N - CO - NH2\n\nPolymerization Reaction: A large number of molecules of the same compound combine together to form a large molecule of heavy atomic mass, at high temperature and pressure and in the presence of a catalyst. This reaction is called polymerization. In such cases, the large molecule is called a polymer and each of the smaller molecules that combine together are called monomers. Under the effect of 1200 atm. pressure, 200°C temperature and O2 catalyst, numerous smaller molecules of ethylene combine into a large polymer molecule of polythene. This reaction is polymerization reaction of ethylene. Here, ethylene molecules are the monomers while polythene molecule is the polymer. In the equation, n denotes the number of molecules.\n\nn(CH2 = CH2) →(O2) 200°C, 1200 atm" }, { "section": "7.4 Examples of a Few Real Life Chemical Reactions", "subsections": [ { "title": "7.4.1 Chemical Reactions in Reality", "text": "We observe many happenings around us everyday which are caused by chemical reactions. For example:\n\n1. Rust on Iron: We use various instruments made of iron everyday like knife, scissors, machete etc. If we keep them exposed in open air, they undergo rusting. Here, iron undergoes reaction with oxygen and water vapor and produces ferric oxide. Since rust is fragile in nature, oxygen and water vapor from air pass through it and continue to corrode the iron. Thus the whole object made of iron is ruined.\n\n2Fe + 1.5O2 + 3H2O → 2Fe(OH)3\n2Fe(OH)3 → Fe2O3.nH2O (Rust)\n\nThe number of moles of water in rust is not fixed. That is why, the formula of rust is Fe2O3.nH2O. Here, the value of n can be 1, 2, 3, 4..... etc. integers.\n\n2. Prevention of Corrosion of Copper and Aluminum: We also use copper- aluminum products in our day to day life. When products made of Cu and Al come in touch with open air, they produce a layer of CuO and Al2O3. This layer acts to prevent the air to come in direct contact with Cu and Al and no more reaction takes place. Thus the decay of Cu and Al is prevented.\n\n3. Relief from the bite of ants and Bee: When ants or bees bite us, we feel pain at the spot of the bite. We use lime on that spot to get relief from the pain. The ant in its mouth or the bee in its sting carries an acid which is the cause of our pain. The lime (base) reacts with that acid and neutralizes it. As a result, we are relieved of the pain.\n\n4. Energy Produced through Respiration: Respiration occurs in every cell of our body. In respiration, basically, the glucose (C6H12O6) molecule is oxidized by O2 and in this process CO2, H2O and energy is produced.\n\nC6H12O6 + 6O2 → 6CO2 + 6H2O + Energy\n\nThe digestion system in the human body forms excess HCl in many of us. To neutralize this acid, many doctors prescribe an antacid type medicine. Antacid is a mixture of Mg(OH)2 and Al(OH)3. These two bases neutralize excess HCl and the patient feels relieved. The equation of the reaction is:\n\n2HCl + Mg(OH)2 → MgCl2 + 2H2O\n3HCl + Al(OH)3 → AlCl3 + 3H2O\n\n5. Natural Gas as Fuel: Natural gas is used as fuel. Maximum percentage of natural gas is composed of methane. When this methane gas is burnt in oxygen, it produces CO2, H2O and heat. When we burn CNG, diesel, petrol, kerosene and octane, they produce the same products.\n\nCH4 + 2O2 → CO2 + 2H2O + Energy" }, { "title": "7.4.2 Ways to Prevent Some Harmful Reactions that Occur in Real Life", "text": "Many products around us are continuously being decayed or eroded due to some chemical reactions. We can make use of our knowledge of chemistry to prevent such decaying and save many of them.\n\n(i) To prevent corrosion of rust on iron, one can paint the outside of the iron products so that it does not come in contact with air. A coating of a comparatively less active metal on iron through electrolysis, which is called electroplating, can also save iron from rusting. The process which lays a coating of zinc on other metals is called galvanizing and the process of tin plating lays a tin coating. The process which lays a coating of a metal on other metals through electrolysis is called electroplating. This way we can save metals from corrosion.\n\n(ii) The roofs and yards of our houses become slippery during the rainy season. We spread sand on those slippery spots. The slippery substance is alkaline. Therefore, it requires some acidic substance to be neutralized. Sand (SiO2) is acidic. This sand neutralizes the alkaline there.\n\n(iii) Sewing needles are kept in coconut oil. The reason is to prevent it from getting rust due to the reaction between oxygen and water vapor." } ] }, { "section": "7.5 Rate of Reaction", "text": "We know that in any reaction, reactants convert to products. Some reactions take less than 1 second while, some take quite a lot of time.\n\nThe amount of products produced from reactants per unit time is called the rate of reaction.\n\nFor example, when AgNO3 is added to the NaCl solution, it takes less than 1 second to create the white precipitate of AgCl. On the other hand, it takes years for a bridge to rust. Reactions that take less time have a higher rate of reaction and reactions that take more time have a lower rate of reaction.", "figures": [ { "caption": "Reactions with different rates, rust on iron, combustion of candle, explosion of bomb", "reference": "Fig 7.03" } ], "experiments": [ { "title": "Experiment on the Rate of Reaction", "description": "Take four test tubes and mark them 1, 2, 3, 4. Take an approximate amount of 0.5 mg sodium carbonate (Na2CO3) or washing soda in each of them. Then add normal water to tube 1 and 2 and hot water to 3 and 4. Now add 1 mL lemon juice (citric acid) or vinegar (4-10% acetic acid) to tube number 2 and 4. Observe the following changes:\n\n1. Which of the test tubes produces gas bubbles?\n2. Which of the test tubes does not produce gas bubbles?\n3. Which test tube produces the maximum number of gas bubbles?\n4. Which test tube produces the minimum number of gas bubbles?\n\nThink: Why does gas come out in a larger amount from one of the tubes of number 2 and 4?", "figures": [ { "caption": "Reaction between sodium carbonate and acetic acid or vinegar", "reference": "Fig 7.04" } ] } ] }, { "section": "7.5.1 Le Chatelier's Principle", "text": "In some reactions products react and turn into reactants again. When the reactants react and produced a new substance that is called a forward reaction. When the products again react and revert back to reactants they are called backward reactions. At the beginning of the reaction, the forward reaction has a higher rate. It decreases gradually with the progress of time. Again, at the beginning, the rate of the backward reaction remains slow but it increases gradually with the progress of time. At a stage, both the rates become equal. This state is known as equilibrium of the reversible reaction. Similarly, over time, the concentration of the reactants decreases and the concentration of the products increases. Eventually, the concentrations of both become stable and remain unchanged over time.\n\nBoth forward and backward reactions continue in equilibrium. The amount of reactants that have already turned into products in the forward reaction are equal to the reactants that have been produced in the backward reaction at this state. Therefore, it appears that the reaction has stopped but in reality it has not. However, in equilibrium, if we change the parameters of the reaction such as temperature, pressure and concentration etc. the equilibrium also changes. Increase and decrease of products in equilibrium of a reversible reaction is controlled by the Le Chatelier's principle. The principle is:\n\nIf a chemical reaction is at equilibrium and an external change occurs in that state, such as a change in pressure, temperature, or density of the substance, then the existing equilibrium of the reaction changes and a new equilibrium is formed that mitigates the effect of the external change.", "figures": [ { "caption": "Chemical equilibrium", "reference": "Fig 7.05" } ], "subsections": [ { "title": "Explanation of Le Chatelier's Principle:", "text": "The effect of temperature, pressure and concentration of reactants in equilibrium can be explained by Le Chatelier's principle.\n\nEffect of Heat on Equilibrium: Let us consider a reversible reaction:\n\nN2 + 3H2 → N2H3 + 92 kJ\n\nThe forward part of this reaction is exothermic; when reactants N2 and H2 react to produce NH3, they also evolve heat. Conversely in the backward part, when NH3 converts to N2 and H2, it absorbs heat. Therefore, heat is required to be applied. Now we shall see according to Le Chatelier's principle, what will happen as we apply heat to this reversible reaction. According to the principle, if heat is applied, the effect due to that heat has to be neutralized. Application of heat will increase the forward reaction, increasing production of heat and that will not neutralize the heat. If the reverse reaction is increased, that will absorb more heat and neutralize the excess heat. Therefore, according to Le Chatelier's principle, we can say that if heat is increased, the reverse reaction will also increase. In other words, the effect of application of heat in exothermic reactions will drive the equilibrium state to the left side, meaning, NH3 converts into N2 and H2.\n\nIn the same way, we can say that the decrease of temperature in equilibrium will increase the exothermic forward reaction and neutralize the effect of lesser heat. The equilibrium will shift from left to right. Reactions that are not affected by temperature will not have any effect on its equilibrium too.\n\nLet us consider another reaction:\n\nN2 + O2 + 180 kJ → 2NO\n\nApplication of heat to this reaction will increase the forward endothermic reaction or the equilibrium will shift left to right; N2 and O2 will react and produce NO. In equilibrium, if heat is decreased, the reverse exothermic reaction will increase reversing the equilibrium right to left; NO will convert into N2 and O2.\n\nEffect of Pressure on Equilibrium: In equilibrium of gaseous reactions, equilibrium of the reaction will change with the change of pressure. In equilibrium, change of the total number of moles of reactants and of products will create effect of pressure. Example:\n\nN2(g) + 3H2(g) → 2NH3(g)\n\nAccording to Le Chatelier, if pressure is applied, the effect of increased pressure has to be neutralized. In the same volume, the gas with the greater number of moles has the greater pressure and the gas with the smaller number of moles has smaller amount of pressure. In the above reversible reaction, the gaseous product has the greater number of moles (1 + 3 = 4) whereas the right side has the smaller number (2). So, to neutralize the effect of increased pressure, the gaseous substance has to shift from larger number to smaller number. The forward reaction will increase and N2 and H2 will produce NH3. In other words, the equilibrium will shift from greater moles to smaller moles. So, if pressure is decreased at equilibrium, according to the principle, to neutralize the effect of decreased pressure, the equilibrium state will shift toward greater moles from smaller moles.\n\nWe can consider another reversible reaction:\n\nN2(g) + O2(g) → 2NO(g)\n\nIn this reaction, mole number of reactants is (1 + 1) = 2 and mole number of product is also 2. Since this reaction has no change in the number of moles, there is no change in pressure too. The reaction does not show any effect of pressure on its equilibrium.\n\nEffect of Concentration on Equilibrium: Equilibrium of all reactions are effected by the concentration of reactants. If the concentration of any reactant in the equilibrium state of the reaction is increased, according to Le Chatelier principle, the concentration of the reactant has to be decreased in order to neutralize the effect of increased concentration. Similarly, if the concentration of any product is increased, the amount of product is neutralized as the reaction reverts and the concentration of reactants is increased. That means, the equilibrium shifts toward left." } ] } ] }, { "chapter_number": 8, "title": "Chemistry and Energy", "start_page": 168, "end_page": 205, "content": [ { "section": "8.1 Chemical Energy", "subsections": [ { "title": "8.1.1 Source of Chemical Energy", "text": "Matter has molecules and atoms. An atom remains connected to another atom because of attraction energy (bond). The energy by which atoms are connected to each other is called chemical energy.\n\nBond Energy: In a chemical bond, the energy by which an atom remains joined with another atom is called bond energy. In sodium chloride, there is an ionic bond between a sodium ion and a chloride ion. There is a covalent bond between carbon and oxygen in carbon dioxide. In iron, one atom is bonded with another due to a metallic bond. In these bonds the energy of attraction that connects one atom to another atom is called the bond energy.\n\nInter Molecular Energy: In a covalent compound, the energy that keeps the molecules combined with each other is called the inter molecular energy. For example, water is a covalent compound. Inter molecular energy combines the molecules of surrounding water with a molecule of water. On the other hand, in the ionic compound sodium chloride, 6 chloride ions surround a sodium ion. There is energy active in between them. Again, each chloride ion is surrounded by 6 sodium ions. They are also combined due to the energy.\n\nThe attraction energy in between ions of an ionic compound is stronger than inter molecular energy present between covalent molecules. That is why the melting point and boiling point of ionic compounds is greater than those of covalent bond substances.\n\nDue to the same reason, ionic compounds remain as solids at room temperature whereas covalent compounds usually remain in liquid or gaseous state at room temperature. However, there are some exceptions like naphthalenes. Even though it is a covalent compound, it remains solid in room temperature.\n\nThe inter molecular energy in a covalent compound consisting of atoms of two elements (HCl) is greater than inter molecular energy in a covalent compound consisting of atoms of the same element (H2)." }, { "title": "Transformation of Energy in Chemical Reactions", "text": "Each substance contains some energy. Usually in chemical reactions, the energy of the reactants is necessary to make the reactions happen or some chemical reactions result in generation of energy. That means, energy is transformed in chemical reactions. The energy required to make a reaction take place or the resultant energy from a reaction may have different forms like heat energy, light energy, electricity, sound etc." }, { "title": "Units of Measurement of Energy", "text": "Earlier, calorie or kilocalorie was used as unit to measure energy. The heat applied to raise the temperature of 1 gram water by 1°C is called a calorie (cal in brief). 1 kilocalorie is 1 thousand calories. Kilocalorie is expressed by kcal.\n\nPresently, the international standard unit to measure all kinds of energy is Joule. A joule is the work done by a force of one newton acting through one metre displacement. It is expressed by the abbreviate j. 1 kilojoule (kJ) is equal to 1000 joule.\n\nThe relation between calorie and joule is 1 cal = 4.18 J" }, { "title": "8.1.2 Classification of Chemical Reactions According to Change of Heat", "text": "Some reactions occur spontaneously while some reactions require the application of energy. Reactions that occur spontaneously heat is produced during the conversion of reactants to products. According to the change of heat, reactions are of two kinds: (i) Exothermic reactions and (ii) Endothermic reactions. In exothermic reactions, the value of ΔH is negative and in endothermic reactions, the value of ΔH is positive. Here H is the heat contained of substance.\n\nAny substance has a specific energy at a specific temperature. This energy is called internal energy. If we express the total internal energy of reactants in a reaction with H1 and the total energy of the products with H2, then the change of heat energy in that reaction will be:\n\nΔH = Total internal energy of the products (H2) - Total internal energy of the reactants (H1)\n\nIn exothermic reactions, the total internal energy of reactants (H1) is greater than the total internal energy of products (H2). Therefore, the value of ΔH = (H2 - H1) becomes negative. In this reaction, heat is released.\n\nFor example, when in a reaction, the total internal energy of reactants 50 kJ/mol and the total internal energy of products is 20 kJ/mol, ΔH = (20–50) = -30 kJ/mol.\n\nAgain, in endothermic reactions, the total internal energy of reactants is lesser than the total internal energy of products. Therefore, the value of ΔH = (H2 - H1) in this case is positive. For example, when in a reaction, the total internal energy of reactants 70 kJ/mol and the total internal energy of products is 80 kJ/mol, ΔH = (80–70) = +10 kJ/mol.", "figures": [ { "caption": "Exothermic and endothermic process", "reference": "Fig 8.01" } ] }, { "title": "Exothermic Reactions", "text": "The chemical reactions in which heat is evolved are called exothermic reactions. An equation of an exothermic reaction can be written with the word Heat at the right side. If it is written with the expression ΔH, the value will be negative (-). You have seen the natural gas burnt while cooking, produces heat. If water is poured on dry lime, that substance becomes hotter. Methane is the basic ingredient of cooking gas. When we burn this gas, each mole of it reacts with oxygen of air and produces carbon dioxide, water and 890 kJ heat.\n\nAgain, dry lime is calcium oxide (CaO). When water is poured in it, calcium hydroxide Ca(OH)2 is produced. Alongside, 63.95 kJ/mol heat is produced. That's the reason of it being heated.\n\nIn both the above reactions, the total internal energy of reactants is greater than the total internal energy of products. That extra energy has evolved as heat in the reaction." }, { "title": "Endothermic Reactions", "text": "Chemical reactions in which heat is absorbed are called endothermic reactions. They are also called heat absorbing reactions. In the equation of endothermic reactions, on the left side, the heat may be recorded. If it is written with the expression ΔH, the value will be positive (+). In villages, the outer shells of snails or oysters are gathered and burnt to produce edible lime. Actually, these casts contain about 98% calcium carbonate. The heat from the fire transforms this calcium carbonate into calcium oxide and carbon dioxide. The calcium oxide is lime which remains as left over and the carbon dioxide mixes in the air.\n\nOr,\n\nCaCO3(s) → CaO(s) + CO2(g) ; ΔH = 176.8 kJ / mole", "figures": [ { "caption": "Preparation of lime from oysters.", "reference": "Fig 8.02" } ] }, { "title": "8.1.3 Calculation of Heat Change in Chemical Reactions Using the Bond Energy", "text": "The value of ΔH in a chemical reaction is determined in two ways: by using internal energy and by using bond energy.\n\nIf internal energy is used, ΔH is calculated by subtracting the total internal energy of the reactants from the total internal energy of products. If bond energy is used, ΔH is calculated by subtracting the total bond energy of products from the total bond energy of reactants. No matter how it is calculated, the value of ΔH for the reaction remains the same.\n\nThe energy required to break the bonds of the atoms of a compound and separate them is called the bond energy. Again, the energy required to form the bonds of atoms of a compound and combine them is called the bond energy.\n\nWhen a chemical reaction takes place, the bonds between the atoms in the reactants break and new bonds are formed in the products. Energy is required to break the bonds in the reactants, and energy is released when new bonds are formed in the products.\n\nIn any reaction, if the total bond energy of reactants is B1, and the total bond energy of products is B2, then the heat change in that reaction will be:\n\nΔH = The total bond energy of reactants (B1) - The total bond energy of products (B2) = Total energy required for breaking the old bonds (B1) - Total energy released in the formation of new bonds (B2)\n\nIn exothermic reactions, the value of B1 is lesser than B2, so the value of ΔH is negative while in endothermic reactions, the value of B1 is greater than B2, so the value of ΔH is positive.", "tables": [ { "caption": "Table 8.01: Bond and Bond Energy", "headers": ["Bond", "Bond Energy (kJ/mol)"], "rows": [ ["C-H", "414"], ["C-Cl", "326"], ["C-C", "344"], ["C=C", "615"], ["N≡N", "946"], ["Br-Br", "193"], ["O-O", "143"], ["H-Cl", "431"], ["H-I", "299"], ["C=O", "724"], ["N-H", "391"], ["O-H", "464"], ["O=O", "498"], ["C=C", "812"], ["Cl-Cl", "244"], ["I-I", "151"], ["H-H", "436"], ["H-Br", "366"], ["H-F", "563"], ["C-O", "350"] ] } ], "examples": [ { "problem": "Determine the heat change (ΔH) in the reaction CH4 + Cl2 → CH3Cl + HCl. Given, bond energy of C-H = 414 kJ/mol, bond energy of C-Cl = 244 kJ/mol and bond energy of H-Cl = 431 kJ/mol.", "solution": "In the reaction CH4 + Cl2 → CH3Cl + HCl 1 mole C-H bond and 1 mole Cl-Cl bond has been broken among the reactants while 1 mole H-Cl bond and 1 mole C-Cl bond has been formed. Therefore,\n\nTotal bond energy applied on reactants to break bonds = (414 + 244) kJ = 658 kJ\n\nTotal bond energy evolved from products to form bonds = (326 + 431) kJ = 757 kJ\n\nThe heat change in the reaction ΔH = (658 - 757) kJ = -99 kJ\n\nSince the value of ΔH is negative here, so the reaction is exothermic. This reaction evolves 99 kJ/mol heat." } ] } ] }, { "section": "8.2 Uses of Chemical Energy", "subsections": [ { "title": "8.2.1 Transformation of chemical energy into different types of energy", "text": "Chemical energy can transform into any type of energy like heat, light, electricity, sound or mechanical energy. Some examples are discussed below.\n\nBurning of Fuel: We get heat and light energy when we burn coal, natural gas, wood etc. This energy is obtained basically from the chemical energy present in these substances. Burning is actually to let a substance react with the oxygen of air. Methane (CH4) is the main ingredient of natural gas. When methane is burnt, it produces carbon dioxide, water vapor, heat and light.\n\nFireworks: The fireworks that you see on the sky during large festivals render light, sound and mechanical energy. The chemical elements inside the fireworks react with each other and the chemical energy in them produces light, sound and mechanical energy.\n\nDry Cell: You are familiar with battery. The batteries used in torches and remotes are dry cells. The chemical ingredients inside a dry cell react with each other and the chemical energy is transformed into electricity.\n\nDaniel Cell: The batteries you see on buses, trucks etc. are Daniel cells. Zinc metallic sticks in zinc sulfate salt solution and copper metallic sticks in copper sulfate salt solution are used to make Daniel cells. The following reaction takes place in this cell:\n\nZn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)\n\nThis reaction turns the chemical energy into electricity." }, { "title": "8.2.2 Chemical Energy and Use of Various Energies Obtained from Chemical Energy", "text": "Chemical energy remains stored in molecules and atoms of elements. When a substance reacts with another, then we get chemical energy. We turn that energy into various energies and put them to use. Chemical energy is the most used of all kinds of energies on earth.\n\nWhen wood or natural gas is burnt for cooking, their chemical energy turns into heat energy. The heat obtained from burning wood is used for making bricks or making earthen pots. Iron, steel and ceramic industries require huge amount of heat. Coal, petroleum, natural gas etc. mineral fuels are used in heat engines. These fuels are burnt in the burning chamber to produce heat and the heat is then turned into mechanical energy to run automobiles, ships, planes, trains etc.\n\nThe first thing that strikes our mind when we talk about chemical energy is photo-synthesis. Plants have chlorophyll in their green parts. Chlorophyll helps them to utilize sunlight and conduct the reaction between water absorbed from the earth through their roots and carbon dioxide from air. Thus, they produce glucose (C6H12O6) and oxygen (O2). This oxygen is released by the plants. This reaction is called photo-synthesis. However, the sunlight that participates in the reaction remains in the plant in the form of chemical energy.\n\n6CO2 + 12H2O →(Chlorophyll, Sunlight) C6H12O6 + 6O2 + 6H2O\n\nBesides, the body of both plants and animals produce fat and protein. They also contain chemical energy. Again, humans and other animals consume them as food. The body of humans and plants can be called chemical engines. Plants get chemical energy from this carbohydrate, protein and fat. This energy turns into heat or other energy. Plants and animals use these transformed energies to conduct different activities. Therefore, it is understood that without chemical energy, life is impossible." }, { "title": "8.2.3 Appropriate Use of Chemical Energy", "text": "Petroleum, coal natural gas etc. are called fossil fuel. These fuels have chemical energy stored in them. Burning these fuels or letting them to react with oxygen, heat energy can be obtained. This heat energy is used for cooking, running automobiles and electricity generation.\n\nBesides providing heat energy, burning these fossil fuels has harmful effects on nature. They produce carbon dioxide. The amount of that every year is 21.3 billion tons of carbon dioxide. This gas is a greenhouse gas, meaning it contains heat. As a result, the world is getting warmer day by day. Again, carbon dioxide reacts with rain water and produces carbonic acid (H2CO3). When it comes down to earth with rain, we call that acid rain, which is very harmful for nature. These bad effects of fossil fuels are imposing a threat to life on earth. Therefore, we need to be meticulous in using fossil fuels. We should not use excess fossil fuel. Excessive use of fossil fuels will end up their reserve. Meticulous use will ensure that the reserve remains for our future and they won't impose any bad effect on our lives." }, { "title": "8.2.4 Importance of Purity of Fuel", "text": "We are constantly making use of various kinds of fuels to get chemical energy. Their purity is an important factor. If we burn them in insufficient air, carbon monoxide is produced alongside carbon dioxide, which is a harmful gas. It is dangerous for our health. Natural fuels are of crude form. They have mixture of compounds of nitrogen, sulfur, phosphorus etc. That is why, these fuels need refinement before being sent to the market. If we burn them without refinement, the oxides of these elements also go in the air. These oxides mix with rainwater and form acids which again come down to earth with rain. The acid rain is:\n\nThis acid rain causes huge damage to our environment. Plants die due to this rain. Water in water bodies turn acidic which makes survival of the fishes and other living bodies tough. Then, the smoke of automobiles consists of carbon monoxide, nitrous oxide and unused methane. In the presence of sunlight, these react to create various poisonous gases. They are known as photochemical smog which is harmful to health.", "figures": [ { "caption": "Acid rain", "reference": "Fig 8.04" } ] }, { "title": "8.2.5 Negative Effects of the Use of Chemical Energy", "text": "We burn fuels in order to get energy. Mainly, we make use of chemical energy through the use of fuels. Although, presently we are using solar energy, nuclear energy, wind energy, hydro energy etc. yet, the major part of our required energy is provided by fossil fuels. We have already learned that every year, we are producing 21.3 billion tons of carbon dioxide gas by burning fossil fuels. Trees take in carbon dioxide in its photo-synthesis process. Besides, some other natural processes use up half of it. The other half remains on earth. As carbon dioxide is a heavy gas, it remains below the atmosphere. It does not undergo reactions with other elements of the atmosphere too. However, it has high heat absorbing capacity. Due to this, the temperature of the earth is increasing day by day. This is called global warming. This global warming is melting the ice of the polar region and thus increasing the sea level. Many countries including Bangladesh are at risk of being submerged. Besides carbon dioxide, some other gases are also contributing to the global warming. It is denoted by the term 'Greenhouse effect.' The gases responsible are known as greenhouse gases. You have already learned about acid rain and photochemical smog. These facts put carbon dioxide as a major portion of the greenhouse gases for harming the atmosphere." }, { "title": "8.2.6 Uses of Ethanol as Fuel", "text": "The other name of ethanol is ethyl alcohol the formula of which is CH3 - CH2 - OH. Burning of this alcohol also produces heat like the fuels already discussed. Therefore, it can also be used in engines of all kinds of vehicles and carriers as a fuel. Many countries including North America are using it as a mix with fossil fuels. All automobiles in USA use fuel with 10% ethanol mixed in it. Thus ethanol may be a suitable substitute for fossil fuels relieving the pressure on our reserves." } ] }, { "section": "8.3 Chemical Process by Electricity", "subsections": [ { "title": "8.3.1 Electrochemical Cells", "text": "Burning fuels, chemical energy can be turned into heat energy which can again be transformed into electrical energy. Now we will learn how to convert chemical energy directly into electrical energy and how to put that electrical energy to use in order to conduct reactions. The mechanism that helps chemical reactions to convert chemical energy into electrical energy directly or uses electrical energy to conduct chemical reactions is called an electrochemical cell. In an electrochemical cell, two metal sticks or graphite sticks are submerged in one or two electrolytic solutions. The sticks are connected directly or through a battery with a metallic wire. The graphite sticks are called electrodes. Electrochemical cells are of two kinds:\n\n(i) Electrolytic Cells: The cell where electricity is driven from an outer source to carry out a chemical reaction inside the cell is called an electrolytic cell.\n(ii) Galvanic Cells: The cell where chemical elements undergo reactions and produce electrical energy is called a Galvanic cell.\n\nThe materials, through which electricity can pass, are called electrical conductors. For example, metals, graphite, molten salt, salt solution, acid and base solutions etc are electrical conductors.\n\nDepending on the mechanism of passing of electricity, conductors are of two kinds: Electronic Conductors and Electrolytes.", "subsections": [ { "title": "Electronic Conductors", "text": "The substances through which electricity is passed by means of electrons are called electronic conductors. You have seen, metals contain metallic bonds. As a result, they contain lots of free electrons. Graphite also contains free electrons. These substances let electricity pass through and for that, they are electronic conductors. For example, iron (Fe), copper (Cu), nickel (Ni) etc. are electron conductors." }, { "title": "Electrolyte", "text": "The substances that let electricity pass in their melted and solution state but do not allow in their solid state and simultaneously brings about a chemical change in that substance are called electrolytes. The electrolytes remain ionized during their melted or solution state. The ions are used by electrolytes to conduct electricity. Ionic compounds and some polar covalent compounds become electrolytes in their molten or solution state. For example, sodium chloride (NaCl), copper sulfate (CuSO4), sulfuric acid (H2SO4), water (H2O), ethanoic acid (CH3COOH) etc. are of this type.\n\nElectrolytes are again of two types:\n\n(i) Strong Electrolyte: The electrolytes that remain completely ionized in molten or solution state are called strong electrolytes. Sodium chloride (NaCl), copper sulfate (CuSO4) and sulfuric acid (H2SO4) are strong electrolytes.\n\n(ii) Weak Electrolyte: The electrolytes that remain ionized at a very little amount in molten or solution state are called weak electrolytes. Water (H2O), ethanoic acid (CH3COOH) etc. are of this type." }, { "title": "Electrode", "text": "Electrode is a metallic or non-metallic electric conductor. They are electronic conductors sunk in the solution of electrolytes. In the electrochemical cell, an element or ion donates an electron to an electrode in an oxidation reaction. The positive ion accepts electrons from the other electrode in the reduction reaction. This way, oxidation-reduction occurs in the whole cell. The electrode where oxidation occurs is called the anode electrode and the electrode where reduction occurs is the cathode." } ] }, { "title": "8.3.2 Electrolytic Cell, Electrolysis and the Mechanism of Electrolysis", "text": "Electrolytic cell uses electricity to conduct chemical reactions. There occurs a chemical reaction at the time of electricity passing through molten or solution of electrolytes, which is known as electrolysis. When electricity passes through molten sodium chloride, it produces chlorine gas at the anode and sodium metal at the cathode. This is electrolysis of sodium chloride:\n\n2NaCl(l) → 2Na(s) + Cl2(g)", "subsections": [ { "title": "Mechanism of Electrolysis of Molten Sodium Chloride", "text": "Take molten sodium chloride in a glassware or ceramic ware. The molten sodium chloride contains sodium ion (Na+) and chloride ion (Cl-) ion. Both of them are able to migrate. Two metallic bars or graphite sticks are submerged into the molten sodium chloride. If we connect one of them to the positive part of a battery and another to the negative part, the anode connected to the positive part of the battery will attract negatively charged Cl- ions while cathodes connected with the negative part of the battery will attract positively charged Na+ ions. Cl- ions will donate electrons at the anode and become chlorine gas. The oxidation at the anode:\n\nCl- → 1/2 Cl2 + e-\n\nOn the other side, Na+ accepts electron from the cathode and becomes metallic sodium. The reduction at the cathode:\n\nNa+ + e- → Na\n\nThe ion that is attracted by the cathode is called a cation and the ion attracted by the anode is an anion.", "figures": [ { "caption": "Electrolysis of sodium chloride in electrolytic cell", "reference": "Fig 8.04" } ] }, { "title": "Identification of Chlorine Gas at Anode with Litmus Paper", "text": "If we collect the gas produced during the electrolysis of molten NaCl in a test tube and hold a wet blue litmus on the test tube, the paper will turn red. That will prove the presence of chlorine gas.\n\nSince Chlorine gas and water undergo a reaction and produce two acids, the blue litmus turns red." }, { "title": "Electrolysis of Concentrated Sodium Chloride Solution", "text": "In concentrated sodium chloride solution, NaCl becomes ionized and produces Na+ and Cl- ions.\n\nNaCl → Na+ + Cl-\n\nThe difference from molten sodium chloride is that the solution contains H+ and OH- ions too as water is partially ionized here.\n\nH2O → H+ + OH-\n\nDuring the electrolysis in this electrolytic cell, Na+ and H+ will go towards the cathode together. We know that H+ ion is more prone to accept electrons than the Na+ ion. So, H+ ion accepts one electron at the cathode and becomes a H atom. Two H atoms again join together and become a H2 molecule. The reaction at the cathode:\n\nH+ + e- → H (Reduction reaction)\nH + H → H2\n\nCl- and OH- go simultaneously towards the anode. We know that OH- ion is more prone to donate an electron than Cl-. However, since the molarity of Cl- in the solution is higher than OH- ion, so it donates electrons at the anode earlier than OH-. One Cl- ion donates an electron at the anode and becomes a Cl atom. Two Cl atoms join together producing a Cl2 molecule. The reaction at the anode:\n\nCl- → Cl + e- (Oxidation)\nCl + Cl → Cl2\n\nNa+ and OH- remain as left over in the container. They undergo a reaction and produce NaOH.\n\nThus, if more than one type of cation and anion is present is a solutions, which cation will be discharged at the cathode first or which anion will be discharged at the anode first depends on three factors. The factors are:", "figures": [ { "caption": "Electrolysis of sodium chloride concentrate solution", "reference": "Fig 8.05" } ] }, { "title": "(i) The Tendency of Cations and Anions to Discharge", "text": "If there are more than one kind of cations in an electrolysis, there is a priority list for the cations which specifies which of them will discharge first. The series is called Reactivity Series of Metals or Electro Chemical Series. Between any two elements of this series, the element above is more reactive and it take parts the reaction earlier than the other. Again, the one ion of element at the lower order between any two elements will accept the electron earlier and discharge or become reduced. For example, among Na+ and H+, H+ is at lower order than Na+ and so, it will discharge accepting electrons earlier and be reduced. Again, Fe2+ is at a comparative lower order between Fe2+ and Zn2+. So, Fe2+ will discharge earlier.", "tables": [ { "caption": "Table 8.02: Electrochemical Series", "headers": ["Cation", "Anion"], "rows": [ ["Li+", "NO3-"], ["K+", "SO42-"], ["Na+", "Cl-"], ["Mg2+", "Br-"], ["Al3+", "I-"], ["Zn2+", "OH-"], ["Fe2+", ""], ["Sn2+", ""], ["Pb2+", ""], ["H+", ""], ["Cu2+", ""], ["Ag+", ""], ["Au3+", ""] ] } ], "text": "There is another series specifying the priority of anions to donate electrons and discharge in electrolysis. This series is called Electrochemical Series of Anions.\n\nThe one that is at the comparative lower order between any two ions in the series will donate an electron earlier and discharge or be oxidized. Between SO4^2- and Cl-, Cl- is situated lower than the other. So, Cl- will donate an electron earlier and be discharge or be oxidized. OH- is at the lower order between Cl- and OH-. So OH- will discharge, donating an electron first and be oxidized." }, { "title": "(ii) Effect of Concentration of Cations and Anions", "text": "When there are more than one cations and anions in the solution, the effect of molarity is a more important factor than the tendency to discharge. The molarity of Cl- ion in 0.1 molar NaCl solution at room temperature will be 0.1 molar. On the other hand, ionizing water, the molarity of OH- ion will be 10^-7 molar. That means the molarity of Cl- ion is 10^6 times larger than that of OH- ion. According to the electrochemical series, OH- is situated lower than Cl- and it is supposed to be the first to discharge. But due to molarity or concentration, Cl- ion in this case will be the first to discharge." }, { "title": "(iii) Nature of Electrode", "text": "Sometimes, the kind of electrode causes an exception in the above two factors of discharge in an electrolytic cell. NaCl aqua solution has two kinds of cations- Na+ and H+. When a platinum electrode is used, then according to the factor (i), H+ discharges and produces H2 gas. If mercury is used as a cathode, Na+ ion will discharge at first." }, { "title": "Electrolysis of Pure Water", "text": "In the electrolysis of pure water, anodes and cathodes of some inert metals are used in electrolytic cells. Usually it is platinum. Water exists a little bit ionized:\n\n4H2O → 4H+ + 4OH-\n\nA few drops of sulfuric acid is added to water to increase decomposition of water. Now, when electricity is passed through, anode attracts hydroxyl (OH) ion and cathode attracts hydrogen (H+) ion. The following reactions take place at the electrodes:\n\nCATHODE: 4H+ + 4e- → 2H2 (Reduction)\nANODE: 4OH- → O2 + 2H2O + 4e- (Oxidation)\n\nHydrogen is produced at the cathode and Oxygen is produced at the anode.\n\nYou may be thinking why some drops of sulfuric acid or some lattice of NaCl is required here. You know, electricity does not pass until it is a complete circuit. Electron is the medium of the flow of electricity in anode, cathode or battery. Water hardly gets ionized. So, pure water acts like non-conductor.\n\nTo increase the conductivity of water, some drops of sulfuric acid is necessary.", "figures": [ { "caption": "Electrolysis of water", "reference": "Fig 8.06" } ] } ] }, { "title": "8.3.3 Use of electrolysis", "text": "Presently, mills and industries have sprung up all over the world. The contributions of electrolysis in the industrial sector is enormous. Production of important compounds, extraction of metals from ores, purification of metals, protection from decay, prevention of rust etc. processes require electrolysis and electrolysis requires electrolytic cells. Some of the usages are described below:\n\nExtraction of Metals: Alkali metals, alkaline earth metals, aluminium etc. active metals are extracted through electrolysis. Usually, the cathodes produce these metals when electricity is passed through the electrodes in the liquids of such metallic compounds or solutions. For example, in the electrolysis of sodium chloride, we find sodium metal at the cathode and chlorine gas at the anode.\n\nIn the electrolysis of molten pure aluminium oxide or alumina (Al2O3) aluminium metal is produced at the cathode and oxygen gas is produced at the anode.\n\nAl2O3 → 2Al3+ + 3O2-\n\nReaction at the anode: 3O2- → 3/2 O2 + 6e-\nReaction at the cathode: 2Al3+ + 6e- → 2Al\n\nPurification of Metals: After extraction, the metals contains various other elements mixed in them. Electrolysis is highly effective to purify these metals. Purification of copper, zinc, lead, aluminium etc. involves the electrolysis process. The same adulterated metal electrode of the adulterated metal is connected to the positive edge of the battery. A pure electrode of the same metal is connected to the negative edge of the battery. When electricity is passed through, the metallic ion from the impure electrode goes into the solution and from the solution the ion is transferred to the pure electrode. As a result, the pure electrode thickens while the impure electrode decays.\n\nElectroplating: Adding a coating of a metal on another metal is called electroplating. The process is used for increasing brightness of a metal or to prevent degradation of a metal. Less reactive metals do not react with oxygen of the air. To prevent degradation of a metal, a coating of a comparatively less reactive metal is given on the outer layer of that metal. Usually, nickel, chromium etc. metals are used in electroplating. Iron rusts and decays when it comes in contact with water vapor and air. Nickel, chromium or silver coating is used on iron. They prevent air and water vapors to come in direct contact with iron. The process is discussed below:\n\nTo electroplate iron products such as a spoon, a solution of AgNO3 is taken in a glass container. The product that will receive the coating is connected to the negative edge of a battery and thus is dealt as a cathode. A silver foil is used as an anode. When electricity is passed in the solution, the metallic Ag atom from the anode donates an electron and goes into the solution as Ag+ ions. This Ag+ ion from the solution accepts an electron from the cathode and sticks itself to the cathode as metallic silver. Thus the coating of silver is done.\n\nDecomposition of AgNO3 in solution: AgNO3 → Ag+ + NO3-\nOxidation at anode: Ag → Ag+ + e-\nReduction at cathode: Ag+ + e- → Ag", "figures": [ { "caption": "Silver electroplating on spoon.", "reference": "Fig 8.07" } ] }, { "title": "Commercial Use of Products with Electrolysis", "text": "We can do many things with electrolysis. Various metals such as sodium, aluminium, zinc, calcium, magnesium etc. are extracted from ores by electrolysis. Besides, purification of copper, gold, silver etc. involves electrolysis. The present world has a great demand for these metals.\n\nWe know that silver and copper has the least amount of resistance. Since silver is a precious metal, copper is generally used in producing an electric wire. Can you imagine how much electric wire is used around the world? Aluminium is another important metal as it is necessary to make utensils. Since the metal is light, it is extensively used in making airplanes. Zinc and magnesium are required to add coatings on iron products. Chromium, nickel, gold, silver etc. are electroplating metals on less precious metals to add brightness. This makes the ornaments more lucrative.\n\nChlorine gas produced from electrolysis of sea water is used as an anti-parasite agent. Sodium hydroxide is used as a raw material in different industries." } ] }, { "section": "8.4 Production of Electricity by Chemical Reaction", "subsections": [ { "title": "Galvanic Cell or Voltaic Cell", "text": "Galvanic or Voltaic cells are those electrochemical cells where the elements within undergo reactions to produce electricity. In a Galvanic cell, usually two electrodes of different elements are submerged in two different electrolytic solutions in two different containers. The more reactive metal electrode is used as the anode and the less reactive metal electrode is the cathode. In a galvanic or voltaic cell, an electrode made of a particular metal must be placed in a solution of a salt of the same metal (electrolyte) so that ions of that metal are present in the electrolyte. For example, if an electrode is made of copper, it has to be kept in CuSO4 solution. Similarly, a zinc electrode is kept in ZnSO4 solution. When the two electrodes are externally connected with a metal wire, electrons can flow from one to other, meaning flow of electricity is ensured. A U shaped salt bridge is created between the two electrolytic solutions. The U shaped glass tube contains KCl salt solution. To make it more clear to you, the structure of a Daniell cell is described below.", "subsections": [ { "title": "Daniell Cell", "text": "The cell was invented by John Frederick Daniell in 1836. It is named after him. Two glass or ceramic containers are taken, one partially filled with copper sulphate (CuSO4) solution and another with zinc sulphate (ZnSO4) solution. A copper stick is dipped in CuSO4 and a zinc stick is dipped in ZnSO4. A U-shaped salt bridge is dipped in the two solutions, as shown in the picture, to connect them. A metal wire is used to connect the two electrodes. A bulb connected at the middle of the wire lights up when electricity starts to flow. Here, a zinc atom donates two electrons to the zinc electrode and turns into zinc ion (Zn2+). It leaves the electrode and goes into the solution. The zinc electrode accepts the two electrons and becomes negatively charged. Then the electrons flow through the connecting wire. Since the metallic zinc turns into Zn2+ in the electrode, so it is an oxidation reaction at the anode:\n\nOxidation at anode: Zn → Zn2+ + 2 e-\n\nNow, the two electrons from the zinc anode enters the copper electrode. Through this electrode, the Cu2+ ion from CuSO4 solution accepts the electrons and turns into metallic copper (Cu). Since the process is reduction here, so the copper electrode is regarded as the cathode electrode.\n\nReduction at cathode: Cu2+ + 2 e- → Cu\nThe total reaction in the cell: Zn + Cu2+ → Zn2+ + Cu\n\nHere an oxidation reaction occurs at the anode because Zinc donates electrons to the anode. But donating electron only does not complete a reaction. The copper ion at the cathode electrode has accepted those electrons and completed the reduction reaction. That means half the reaction has occurred at the anode and the other half at the cathode. So, the reaction at the anode is oxidation half reaction and the reaction at the cathode is reduction half reaction. And the total reaction is a redox reaction.\n\nElectrons from anode enter the cathode through the connecting wire. That means the flow of electricity occurred here or electricity was produced. That proves, a Galvanic cell transforms chemical energy into electrical energy.", "figures": [ { "caption": "Galvanic (Deniell) cell", "reference": "Fig 8.08" } ] } ], "tables": [ { "caption": "Table 8.03: Difference between Electrolytic Cell and Galvanic Cell.", "headers": ["Electrolytic Cell", "Galvanic Cell"], "rows": [ ["The cell where electric energy is used to facilitate a chemical reaction is called an electrolytic cell.", "The cell where a chemical reaction produces electric energy is called a Galvanic cell."], ["In an electrolytic cell the anode is positively charged and cathode is negatively charged.", "In a Galvanic cell, the anode is negatively charged and the cathode is positively charged."], ["Producing substances, electroplating, metal purification etc. involve electrolytic cells.", "Electricity production mechanism like a battery uses this technology."] ] } ] }, { "title": "Electrodes in Galvanic Cells", "text": "There are various kinds of electrodes of Galvanic cell. The easiest to make is a metal-metal ion electrode. This kind of electrode can be made by dipping half or more than half of a stick or foil of a metal in a solution containing ion of the same metal. The written expression of such an electrode can be composed of the metal name followed by its ion with a vertical line in between. For example, if a Zn stick is dipped in a ZnSO4 solution, which makes a zinc metal electrode, it can be expressed Zn|Zn2+. The reaction that occurs here is:\n\nZn →(Zn2+) Zn2+ + 2e-\n\nElectrodes of more reactive metals such as sodium, potassium, calcium etc. cannot be produced in this manner. In such cases, amalgam is commonly used. An amalgam is a mixture of mercury and active metals.", "tables": [ { "caption": "Table 8.04: Electrode and Reaction", "headers": ["Electrode", "Reaction"], "rows": [ ["Zn|Zn2+", "Zn(s) → Zn2+(aq) + 2e-"], ["Cu|Cu2+", "Cu(s) → Cu2+(aq) + 2e-"], ["Fe|Fe2+", "Fe(s) → Fe2+(aq) + 2e-"], ["Ag|Ag+", "Ag(s) → Ag+(aq) + e-"] ] }, { "caption": "Table 8.05: Electrode", "headers": ["Electrode"], "rows": [ ["Li|Li+"], ["K|K+"], ["Na|Na+"], ["Mg|Mg2+"], ["Al|Al3+"], ["Zn|Zn2+"], ["Fe|Fe2+"], ["Ni|Ni2+"], ["Sn|Sn2+"], ["Pb|Pb2+"], ["H2|H+"], ["Cu|Cu2+"], ["Ag|Ag+"], ["Au|Au3+"] ] } ] }, { "title": "Salt Bridge and Its Use", "text": "You have seen in the Daniell cell, metallic zinc donates two electrons to become zinc ion at anode. This electron is conducted through the connecting wire towards the cathode. As a result, the ion at the anode solution increases.\n\nOxidation half reaction at anode: Zn → Zn2+ + 2e-\n\nOn the other hand, the Cu2+ ion in the CuSO4 solution at the cathode accepts the two electrons and turns into charge neutral Cu atom without changing the composition of SO4^2- ion. As a result, the solution becomes negatively charged and the flow of electricity stops within a while. The salt bridge comes into effect at this stage. A chemical substance named agar-agar mixed with KCl is put inside a U-shaped tube. It creates a gel like substance which is called the salt bridge.\n\nBoth K+ and Cl- ions in this substance have the same velocity. Two cotton buds at the two faces of the bridge (like in the fig) help connect the two solutions externally.\n\nNow, the surplus charges in the anode are joined by the same number of Cl- ion from the bridge in the anode solution. Similarly, the reduced number of positive charges in cathode solution is joined by K+ ions from the bridge. Thus, the charge neutrality of both the solutions is maintained and the flow of electricity is continued.", "figures": [ { "caption": "Salt bridge in cell", "reference": "Fig 8.09" } ] }, { "title": "Dry cell", "text": "Dry cell is a kind of Galvanic cell. Dry cell transforms chemical energy into electrical energy. We use dry cells in torch lights, TV remotes, toy remotes etc. Dry cell is also composed of an anode and a cathode.\n\nA small container made of zinc is used as an anode in a dry cell. The container is filled with a paste of manganese dioxide (MnO2), ammonium chloride (NH4Cl), zinc chloride (ZnCl2) and distilled water. A carbon (graphite) stick is inserted at the center of the container to act as a cathode. When two wires connect the two edges (positive and negative) of a bulb or electronic item with the zinc container and the carbon stick, the following reaction occurs:\n\nZinc at the anode donates two electrons and becomes Zn2+:\nAnode reaction: Zn → Zn2+ + 2e-\n\nThese two electrons come to the carbon rod through the connector and combine with ammonium ion (NH4+) and manganese dioxide (MnO2) to produce ammonia gas (NH3), dimanganese tri-oxide. The reaction:\n\nCathode reaction: 2NH4+ + 2MnO2 + 2e- → 2NH3 + Mn2O3 + H2O", "figures": [ { "caption": "Dry cell", "reference": "Fig 8.10" } ] } ] } ] }, { "chapter_number": 9, "title": "Acid - Base Balance", "start_page": 206, "end_page": 232, "content": [] }, { "chapter_number": 10, "title": "Mineral Resources: Metal- Nonmetal", "start_page": 233, "end_page": 260, "content": [] }, { "chapter_number": 11, "title": "Mineral Resources: Fossils", "start_page": 261, "end_page": 286, "content": [] }, { "chapter_number": 12, "title": "Chemistry in Our Lives", "start_page": 287, "end_page": 304, "content": [] } ] }