Is Matter Around Us Pure Chapter 2 CBSE Notes Class 9 DailyHomeStudy
We have studied the physical nature of matter in previous chapter. Now in this chapter, we will study and know about the chemical nature of matter.
• Classification of Matter on the Basis of Chemical Composition
A complete classification of matter into fundamental groups is a difficult task. On the basis of chemical composition, the-matter exists either as a single substance or, as a mixture containing two or more substances.
• A sample of matter containing only one substance is called a pure substance.
A sample of matter containing two or more substances is called a mixture.
What is a substance?
A substance may be defined as follows: A kind of matter that cannot be separated into other kinds of matter by any physical process is called a substance? For example, iron, sucrose (cane sugar), water, sodium chloride etc are substances. The composition of a substance is the same throughout even at the atomic or molecular level.
What are the characteristics of a substance?
A substance shows the following characteristics:
■ A substance contains only one kind of atoms or molecules.
• A substance is perfectly homogeneous.
■ A substance has a definite composition which does not change with time.
■ A substance has definite melting point, boiling point, density etc. Pure substances can be further classified into
♦ Elements ♦ Compounds
How to check the purity of a substance?
Each substance has definite (or fixed) melting point, boiling point, density, refractive index etc. These properties are very sensitive to the impurities. Therefore, the purity of any substance can be checked by determining its melting and boiling points, or any other property. The melting and boiling points at 1 atm pressure for some common substances are given in Table 2.1.
Mixtures
What is a mixture?
A mixture is defined as follows: A mixture is that form of matter in which two or more substances (elements or compounds) are present in any proportion. The constituents of a mixture can be separated by simple laboratory methods. The composition of a mixture is not fixed. The constituents of a mixture may be present in any proportion. For example, air is a mixture of mainly oxygen, nitrogen; smaller amounts of carbon dioxide (CO2), dust particles etc., are also present in the air.
What are the type of Mixture?
A mixture may be homogeneous or heterogeneous depending upon the nature of the substances present therein.
• Homogeneous mixture
A mixture which is perfectly uniform in its composition and properties throughout is called homogeneous mixture. Liquid homogeneous mixtures are called solutions. Kerosene is a homogeneous mixture of many hydrocarbons, Solution of common salt in water, some common alloys (e.g., brass) etc. are homogeneous mixtures.
• Heterogeneous mixture
A mixture which has different compositions and different properties at different locations in the mixture is called heterogeneous mixture. For example, muddy water from a pond, Mixture containing sugar and sand are heterogeneous mixtures.
Some other heterogeneous mixtures are,
♦ A mixture consisting of sodium chloride (or common salt) and iron powder (or filings).
♦ A mixture consisting of common salt and sulphur.
♦ A mixture consisting of an oil and water. Depending upon the physical states (gas, liquid or solid) of the components, the following types of mixtures are possible.
What are the characteristics of a mixture?
Mixtures show the following characteristics.
• In mixtures, the constituents may be present in any proportion.
• Mixtures show the properties of all the constituents present therein. For example, a mixture containing sugar and salt will be salty-sweet.
• During the preparation of a mixture, no energy such as heat, light and electricity is either absorbed or evolved. Mixtures (except solutions) are heterogeneous.
• The components of a mixture can be separated by simple physical methods.
Solutions
What do you mean by Solution?
A lump of sugar when placed in tea-water disappears, and the tea-water becomes sweet. Where is sugar gone? Why does the tea-water taste sweet? The sugar placed in tea-water gets dissolved in it, but remains unchanged. This is an example of a solution. Sharbat is a solution of sugar in water. Sea water is another example of a solution. But before we discuss solutions in detail, let us learn something about the term’s solute, solvent and solution. We describe these terms here.
What is meant by a solution?
A solution may he defined as follows: A homogeneous mixture of two or more substances is called a solution.
• When a small amount of sodium chloride is dissolved in water a homogeneous mixture so obtained is called a solution of sodium chloride in water.
The solution of sodium chloride in water is homogeneous because the properties of the solution are the same throughout the solution. This means that if we take out 1 mL samples from different parts of this solution, it will have
♦ the same degree of salty taste, and
♦ the same concentration. It means, all 1 mL samples of this solution will contain the same number of sodium chloride and water molecules. Some other common solutions are,
• Sugar solution in water.
• Copper sulphate solution in water.
• Vinegar (vinegar is a solution of acetic acid in water).
• A homogeneous mixture of two (or more) miscible liquids is also called a solution (or true solution). For example, ethanol (ethyl alcohol) dissolves in water to give a solution of ethanol (ethyl alcohol) in water.
• Copper sulphate solution in water.
• Vinegar (vinegar is a solution of acetic acid in water).
• A homogeneous mixture of two (or more) miscible liquids is also called a solution (or true solution). For example, ethanol (ethyl alcohol) dissolves in water to give a solution of ethanol (ethyl alcohol) in water.
♦ Aqueous solutions of low molecular mass solutes are true solutions. A solution in which size of the solute particles is about 10-10 m is called a true solution. In a true solution, the solute particles and the solvent molecules cannot be distinguished even under a microscope. In a true solution, the solute particles are trapped into the spaces between the solvent molecules. For example, solutions of sodium chloride, copper sulphate, glucose, etc., in water are true solutions.
• Solid solution. Homogeneous solution of a solid into another solid is called a solid solution. Common metal alloys are solid solutions. The gold used in making jewellery is a solid solution containing gold and small quantities of copper or silver.
What is meant by solute and solvent?
A solution is obtained when a substance is dissolved in another substance. The substance which is dissolved to obtain a solution is called solute, whereas the substance in which the solute is dissolved is called solvent. For example, when sugar is dissolved in water to obtain a sugar solution, sugar is the solute and water is the solvent.
In general, the component present in larger amount in a solution is called the solvent, whereas the component present in smaller amount is called the solute. Most common solutes are solids, and solvents are liquids. However, solutes may also be liquids and gases. In some solutions, the solvent may be a gas or a solid. Some typical combinations of solute and solvent are given in Table 2.3.
What are aqueous solutions?
Solutions in which water is the solvent are called aqueous solution. For example, when sugar is dissolved in water, the solution obtained is called an aqueous solution of sugar.
What are nonaqueous solutions?
The solutions obtained by dissolving a solute in any solvent other than water is called nonaqueous solutions (nonaqueous means without water). For example, if a solute is dissolved in any solvent such as benzene, alcohol, ether, carbon disulphide, carbon tetrachloride, acetone, etc., the solution obtained is called a nonaqueous solution. Some commonly used nonaqueous solutions are,
• solution of sulphur in carbon disulphide.
• solution of iodine in carbon tetrachloride.
• solution of iodine in alcohol (tincture of iodine).
What are the characteristics of a true solution?
A true solution (or simply a solution) shows the following characteristics:
• A true solution (or simply a solution) is a homogeneous mixture That is, in a true solution, the solute and solvent molecules cannot be distinguished even under a microscope. The composition and properties of a true solution are the same throughout.
• In a true solution, the solute particles are very small, of the order of about 10-1° m.
• A true solution is clear and transparent.
• A true solution does not scatter light.
• The components of a true solution (the solute and the solvent), cannot be separated by filtration. This is because both solute particles and the solvent molecules are very small as compared to the pores in the filter paper.
▪ The solute particles in a true solution do not settle down.
What are the advantages of preparing/using solutions?
In a solution, the solute and the solvent may be present in the form of molecules, ions or both. Solutions are prepared for the following purposes.
• For carrying out reactions.
For a reaction to take place, the reacting molecules or ions, must come closer to each other. In solutions, the reactants can come closer easily. So, reactions in solutions take place at a faster rate because the reactants in solutions are available in the form of molecules or ions.
■ For dissolving medicines.
Certain medicines are given to patients in the form of their solutions in suitable aqueous or nonaqueous solvents, such as alcohol. For example, saline glucose solution contains glucose and sodium chloride in water. This solution is administered to a patient suffering from dehydration.
Concentration of a Solution
How is the concentration of a solution described?
Most reactions are carried out in solutions. In order to perform calculations, it is necessary to know concentrations of the solutions. The quantity of solute dissolved in a given mass or volume of the solution or the solvent is called concentration of the solution. There are many ways to describe the concentration of a solution. The simplest way to express the concentration of a solution is in terms of mass- by-mass or mass by volume percentage of solute in solution.
Mass-by-mass per cent (or per cent by mass)
The mass of solute in grams per 100 grams of the solution is called mass percent of solute in the solution. For example, a 5% solution of sodium chloride means that 5 grams of sodium chloride are present in 100 grams of the solution.
Mathematically, mass percent of a solute in solution can be expressed
(Mass of solute x 100)/ Mass of solution
Both, the mass of solute and that of the solution must be expressed in the same mass units, viz., both in grams or both in kilograms, etc. However, when a solute is present in trace quantity (very small quantity), the concentration is expressed in the units of parts per million (abbreviated as ppm). For example, a sample containing 5 grams of solute in 106 grams of a solution is said to have a concentration of 5 ppm. The composition of gaseous mixtures is also expressed in ppm units based on the volume ratio. For example, 10 mL in 106 mL corresponds to 10 ppm.
Example
Question: A solution is prepared by dissolving 15.0 g of sodium chloride in 200.0 g of water. What is the mass-by-mass per cent of sodium chloride in this solution?
Answer
Mass of sodium chloride dissolved = 15.0 g
Mass of water taken = 200.0 g
So, Total mass of the solution = 200.0 g + 15.0 g = 215.0 g
From the detinition,
So, the mass-by-mass concentration of sodium chloride in solution is 6.98%,
Mass-by-volume percentage
The concentration of a solute in any solution can also be expressed in terms of mass by volume percentage. This is defined as follows:
The unit of mass-by-volume percentage may be expressed as gram per millilitre (g/mL), gram per litre (g/L), or kilogram per litre (kg/L}4 etc.
Example:
Question: 11.0 g of sugar is dissolved in water to make up a volume of 55 ml. What is the concentration of sugar solution in terms of mass-by-volume percentage?
Answer
Mass of sugar dissolved, m = 11.0 g
Volume of the sugar solution, v = 55 mL
Mass-by-volume percent of sugar in solution = 11.0 g x 100/ 55 mL = 20%
What is an unsaturated solution?
A solution in which some more solute could be dissolved at any fixed temperature is called an unsaturated solution. For example, a solution of sugar in which some more sugar could be dissolved without changing its temperature is called an unsaturated solution of sugar.
What is a saturated solution?
A solution in which no more solute can be dissolved at any fixed temperature is called a saturated solution. In other words, a solution which contains the maximum possible amount of solute at any given temperature is called a saturated solution. In a saturated solution, dissolved and undissolved solutes are in equilibrium with each other. Any solution containing more solute than that required to prepare a saturated solution, at any fixed temperature, is called supersaturated solution. The state of supersaturation is a metastable state. How to prepare the saturated solution of a substance
Suspensions
Suspensions are heterogeneous in nature.
What are suspensions?
A suspension is a heterogeneous mixture in which very fine particles (size: 10-7 m or more) of a solid are dispersed in any medium (liquid or gas). In any suspension, fine particles of the solid remain suspended in the medium. Muddy pond water, Smoke coming out of a chimney of a factory, Chalk-water mixture and Coarse Lime particles in water are the examples of suspensions.
What are the properties of suspensions?
Following are the characteristic properties of suspensions:
• Heterogeneous nature. A suspension is a heterogeneous system.
• Visibility. The particles in a suspension can be seen with naked eyes or under a simple microscope. ■ Particle size. In a suspension, the size of the particles is of the order of 10-7 m or larger.
• Sedimentation. The particles in a suspension have a tendency to settle down. Very fine particles, however, remain suspended in the medium.
■ Separation by filtration. Larger particles in a suspension can be separated from the liquid or air by filtration.
Colloids
What are colloids?
A homogeneous-looking heterogeneous mixture in which particles, having size between 1 and 100 nm (nm is the symbol for nanometre: 1 nm = 10 m) are dispersed in a continuous medium is called a colloid Colloids are commonly called sols. In a colloid, particles of the dispersed phase may be 10 to 1000 time, the size of a small molecule. The continuous medium in a colloid is called the dispersion medium and the particles form the dispersed phase. The particles of the disperse phase are commonly called colloidal particles.
Examples: Milk, Office paste (gum), Blood, Toothpaste, Jelly, etc., are colloids. Fog is a common colloid, in which water droplets (the dispersed phase) are dispersed in air (the dispersion medium). Depending upon the nature of the dispersed phase and the dispersion medium, the colloids may be classified into various types.
What are the properties of colloid?
■ Separation of colloidal particles by filtration. Colloidal particles can easily pass through the pores of a filter paper. Therefore, colloidal particles cannot be separated by ordinary filtration.
■ Stability. Colloids are unstable unless stabilized by adding suitable stabilizer. The colloidal particles tend to come together and settle down.
• Brownian movement of colloidal particles. When seen under a microscope, the colloidal particles in a colloid are seen to be moving in a random (zig-zag) fashion. This zig-zag motion of particles in a colloid is called Brownian motion.
■ Light scattering by colloidal particles — Tyndall effect.
When a of light is passed through a colloid kept in a dark room, the path of the light beam through the colloid becomes visible. This occurs due to the scattering of light by the colloidal particles. The scattering of light by the particles in a colloid is called Tyndall effect. True solution doesn’t scatter light. Therefore, true solutions do not show Tyndall effect.
• Electrophoresis. Many colloidal particles have electrical charge on them, i.e., colloidal particles may have positive or negative charge on them. So, when electric current is passed through a colloid, the Ne, colloidal particles move towards the oppositely charged electrode. The movement of colloidal particles under the influence of electric P field is called electrophoresis.
What are the applications of colloids?
Due to their unique properties, colloids find many applications in our daily life and industry. Some typical applications of colloids are described below:
■ In our food. Many items in our food contain colloidal materials. For example, milk, starch, proteins, fruit-jellies are colloidal in nature.
• In medicines. A large number of medicines and pharmaceutical preparations are colloidal in nature. Some of them are in fact emulsions. Such colloidal medicines are easily adsorbed by the both tissues and, therefore, are more effective. For example, colloidal gold, calcium, silver is used in medicines or as ointments.
Colloids are important in understanding certain natural processes. For example, raw natural rubber (latex) and clay in soil are colloidal in nature. Formation of deltas in the sea at the mouth of a river is due to the precipitation (or coagulation) of the colloidal clay in the river water.
How to Separate Pure Substance from a Mixture?
Most materials occur in nature as mixtures containing two or moil constituents. For making use of the constituents, it is necessary separate the constituents of a mixture.
The components of any mixture can be separated by simple laboratory methods.
The choice of method depends upon the basis of differences in the properties (such as Density, Particle size, Solubility, Boiling/Melting points, Volatility, behaviour towards magnet etc.) of the components of the mixture. To choose a suitable method for separation, one should find out a property of the component which is different from that of the others. Some most commonly used methods for separating the constituents of a mixture are listed below:
What is the purpose of separating the constituents of a mixture?
■ Magnetic separation method— For separating magnetic material from non-magnetic Materials.
■ Winnowing, Hand picking and Sieving— For separating a solid from other solid.
■ Sedimentation, Filtration, Evaporation- For separating solid from liquid.
■ Crystallisation- For obtaining pure crystalline solid from impure solid sample or an impure solution of the solid.
■ Filtration – Separating an insoluble solid from the liquid.
■ Sublimation- For obtaining pure sample of a solid from other solids.
■ Distillation- For separating the components of a mixture containing two miscible liquids having boiling point differing by 20°C or more.
■ Centrifugation- For separating finer particles present in a liquid.
■ Chromatography- For separating coloured components of a mixture. The constituents of a mixture are separated for the following purposes:
■ To remove any harmful or undesirable constituents – For example, small pieces of stones and undesirable seed grains are removed from rice and dais before cooking.
■ To obtain pure sample of a substance-Impurities present in any substance are removed to obtain a pure sample of the substance. Pure substances are needed in medicines, research, industry and also in daily use.
■ To obtain useful constituents-A mixture may contain one or more useful constituents. These should be separated for their proper use. For example, petrol, diesel, kerosene etc., are obtained from crude petroleum by a method called fractional distillation.
Separating a solid from other solids which differ in their density, particle size
The desired solid can be separated from a mixture of solids by various methods, such as winnowing, handpicking and sieving.
Winnowing is based on the property that grains are heavier than husk and hay.
Hand-picking and sieving are based on particle size difference.
Separating a solid that sublimes from other solids which do not sublime
Changing of a solid into vapour by heating is called sublimation. The substance that undergoes sublimation is called sublime. Sublimation method is used for separating substances which on heating change directly into vapour (i.e., sublimation on heating). The vapour on cooling gives pure substance in solid form which is called sublimate.
Substances like Camphor, Ammonium chloride, Naphthalene (mothballs), Benzoic acid and Iodine sublime on heating. Dry ice (solid carbon dioxide) sublime at room temperature.
Separation of a magnetic material from the nonmagnetic materials
The magnetic materials can be separated from the nonmagnetic materials by magnetic separation method. Iron is a magnetic material. Therefore, iron filings can be recovered from a mixture containing some nonmagnetic substances such as coal powder, sulphur powder, sand etc.
Separating a solid from its mixture with a liquid
The components of a mixture containing a solid in a liquid can be separated by any one of the following methods.
- Sedimentation and decantation
- Filtration
- Evaporation
- Crystallisation
- Distillation
- Centrifugation
These are described below:
Separating insoluble solids from liquids
The insoluble solids can be separated from liquids by the following methods:
By Sedimentation and Decantation
Sedimentation and decantation are used for separating coarse particles of a solid which is insoluble in any liquid.
For example, the coarse particles of sand in muddy water can be separated by decantation. Before cooking, rice, pulses etc., are washed with water. The wash-water is removed by decantation.
During sedimentation, the heavier coarse particles settle down quickly. Fine particles of clay settle down very slowly. The finer particles can be made to settle down faster by dissolving a small quantity of alum in muddy water. This method is called loading.
By Filtration
This method is used for separating fine insoluble solid particles from any liquid. In this method, the mixture is allowed to pass through a filter. Filter is a medium with fine pores. The insoluble solid particles are retained by the filter, and the clear liquid is collected as the filtrate.
Commonly used filters are a piece of muslin cloth, filter paper etc.
A layer of cotton or a layer of river bed sand can also be used as a filter. Now-a-days, special ceramic filters are used to obtain high purity drinking water.
In filtration, size of the pores in the filter is very important. For good filtration, the pores in the filter should be smaller than the size of the particles to be removed. An experimental set-up for filtration uses filter paper.
Filtering tea by using a strainer is an example of filtration. Here, the tea leaves are retained by the strainer. Tea-strainer cannot be used for filtering turbid water.
Obtaining pure solid from impure solid sample by crystallisation
Pure solid can be obtained from its impure sample by crystallisation. The process of crystallisation is described in the following activity.
separating a soluble solid from its solution by evaporation
Evaporation is used to recover a solid substance from its solution. Evaporation can be made quicker by heating the solution.
Separation by Distillation
Separating pure solvent (liquid) From the solution of a soluble salt by distillation
Pure solvent can be obtained from the solution of a soluble salt b% distillation.
Separating the components of a mixture containing two miscible liquids having boiling point differing by 20°C or more
The components of a mixture of two miscible liquids having boiling points differing by 20°C or more can be separated by distillation.
Separating the components of a mixture containing two or more miscible liquids having boiling points within a narrow range of temperature
When the boiling points of two or more liquids in a mixture do not differ much, the simple distillation does not give complete separation.
To have complete separation of liquids, a modified version of the distillation technique is used. This technique is called fractional distillation. In this method, the vapour from the boiling liquid mixture moves up through a glass column packed with glass beads.
The vapour of high boiling liquid gets condensed in the column and return back to the distillation flask. The vapour of the low boiling liquid moves higher in the column, leave the column from the exit near the top. These vapours get condensed in the condenser and get collected in a flask.
The high boiling liquid is left behind in the distillation flask.
One typical application of the fractional distillation, technique on commercial scale is the refining of crude oil (petroleum) to get petroleum gas, petrol, kerosene, diesel lubricating oil, fuel oil.
Separation of two immiscible liquids using a separating funnel
The liquids which do not dissolve in each other are called immiscible liquids. Immiscible liquids can be separated from each other by using a separating funnel. This method is based on difference in the densities of the two liquids. This method is used for separating two immiscible liquids, such as, oil and water.
Separation of finer particles present in a liquid by centrifugation
The particles which in very small and can easily pass-through filter paper can be separated by centrifugation.
In this method, the mixture containing suspended particles is rotated at a high speed in a centrifuge.
The denser particles settle down to the bottom of the container. The lighter particles stay at the top.
Centrifugation method is also used for separating cream from milk When milk is rotated at high speed, the cream collects in the centre and is removed through an outlet.
In case, the centrifuge machine is not available, one can use domestic churner for separating cream from the milk. You can also separate butter from curd with the help of a churner.
Applications of churning/centrifugation
• Used in washing machines to squeeze out water from the washed we clothes.
■ used for separating cream from milk and butter from curd.
• Used in diagnostic laboratories for testing blood/urine.
Separating the coloured components of a mixture by chromatography
The coloured components of a mixture can be separated by a technique called chromatography (Kroma in Greek means colour).
This technique is based on the principle of distribution. There are many different kinds of chromatographic techniques used these days. Here we illustrate the use of chromatographic technique by using a filter paper strip (called paper chromatography)
Water Purification System For City/Town Water Supply
Big cities need a very large amount of purified water for its people. This demand of purified water is met by purifying raw water taken from a river or a lake. The river/lake water is processed to make it fit for drinking through the following steps:
■ Sedimentation: The raw water from the river is pumped into the settling tank. Here, heavier particles present in the water settle down. The supernatant water is then sent to another settling tank.
■ Loading: Here, alum (also called potash alum) is added to make the finer suspended particles of clay settle down.
■ Filtration: The supernatant water from the second tank is then allowed to pass through a sand and gravel filter. This removes all suspended impurities from the water.
■ Aeration: The filtered water is then aerated to kill micro-organisms and saturate water with oxygen.
■ Chlorination: The aerated water is then mixed with a calculated amount of chlorine. Chlorination kills harmful micro-organisms. This process is called sterilisation of water.
Physical and Chemical Changes
What is a physical change?
A physical change may be defined as follows:
A change in which only the physical properties of the substance get changed, while its chemical composition remains unchanged, is called a physical change.
During a physical change, physical properties such as, colour, volume, size and shape, magnetic properties etc., of the substances may change. For example, when sugar is added to water, it disappears to form its solution. In solution, both water and sugar retain their properties. Sugar can be recovered from its solution by evaporating water. Some typical physical changes are
• Evaporation/condensation of water (or any other liquid).
• Dissolution of common salt or sugar in water.
• Crystallisation of a substance from its solution.
• Magnetisation of an iron piece, and demagnetisation et a magnet.
What are the characteristics of a physical change?
A physical change is characterised by the following properties:
• In a physical change, only the physical properties of the substances undergo change. The chemical properties of the substances remain unchanged.
■ In a physical change, no new substance is formed.
• Physical changes are temporary and can be reversed easily, i.e., the original form of the substance can be obtained easily by simple methods.
What is a chemical change?
A chemical change may be defined as follows:
A change in which chemical composition and chemical properties of the reacting substances undergo a change is called a chemical change.
Thus, due to a chemical change, the nature of the reacting substance is completely changed, and a new substance is formed. The new substance so formed is called the product. Properties of the product are different from those of the original substance. For example, when carbon is burnt, carbon dioxide is produced. Carbon dioxide has properties entirely different from those of carbon. Thus, the burning of carbon (or coal) is a chemical change.
Carbon (s) + Oxygen (g) à Carbon dioxide (g)
Carbon (s) is usually black solid,
Oxygen (g) is used from air
Their mixture makes the colourless gas which turns limewater milky (noncombustible)
Some common chemical changes are
• Burning of coal (or carbon), wood, paper etc.
• Burning of a candle.
■ Souring or curdling of milk.
• Burning of a matchstick.
■ Burning of magnesium in air.
■ Ripening of fruits, and growing of a plant into a tree.
• Digestion of food.
■ Rusting of iron.
• Bursting of a cracker.
What are the characteristics of a chemical change?
A chemical change is characterised by the following properties:
■ In a chemical change, the chemical composition and chemical properties of the reacting substance are completely changed. For example, during the burning of coal, the dark coloured solid coal gets converted into a gaseous substance called carbon dioxide. The composition and properties of carbon dioxide are entirely different from those of coal.
■ Whenever a chemical change takes place, one or more new substances are formed. For example, during the burning of coal, the new product formed is carbon dioxide.
• A chemical change cannot be reversed easily, i.e., a substance undergoing chemical change cannot be regained by simple methods. For example, it is not possible to get back milk after it is converted into curd.
■ A chemical change is a permanent change. For example, a grown tree cannot be converted back into a small plant.
■ During a chemical change a certain amount of energy in the form of heat, light or sound energy, is either absorbed or evolved. For example, when a cracker bursts, heat, light and sound energies are evolved.
Types of Matter
Based on the chemical constitution, matter is classified into two kinds — substances and mixtures.
• Substances are further classified into elements and compounds.
• Elements are further classified into three kinds — metals, nonmetals and metalloids.
Elements
What is an element?
Elements are the basic constituents of till matter. An element is the simplest form of matter, which cannot be split into simpler substances by any chemical or physical method.
In terms of the atomic theory, an element is composed of atoms of the same kind.
Some common metals, nonmetals and metalloids are given following
Metals
Gold Silver Copper
Nonmetals
Hydrogen Oxygen Nitrogen
metalloids
Boron Silicon Germanium
Only a few elements occur in their pure form. Most elements are present in nature in the combined form, i.e., in the form of their compounds. Common elements cannot be made in a laboratory. However, certain elements can be made in very small amounts by using special techniques in laboratories.
Chemical Compounds
All compounds are formed as a result of chemical reactions. That is why, compounds are also called chemical compounds.
What is a chemical compound?
Two or more elements combine together chemically to form a new substance called compound. Compounds are commonly termed as chemical compounds, because these are formed due to a chemical reaction between two or more elements.
A compound is a pure substance made up of two or more elements combined chemically in a definite (or constant) proportion by mass (or by weight). For example,
■ Water is a chemical compound made up of hydrogen and oxygen combined in the ratio 2:1 by volume, or 1:8 by mass (2 g of hydrogen combines with 16 g of oxygen).
■ Pure sodium chloride (NaCl) contains 60.66% of chlorine by mass.
What are the characteristics of a chemical compound?
What are the characteristics of a chemical compound?
A chemical compound has the following characteristics
• A chemical compound is obtained by the chemical combination of two or more elements in a definite proportion by mass.
• Compounds are homogeneous, i.e., their properties are the same throughout.
• The chemical and physical properties of a compound are entirely different from those of the constituent elements. For example, hydrogen is a combustible gas, while oxygen is a supporter of combustion, but their compound, water is neither combustible nor a supporter of combustion.
■ During the formation of a compound from its elements, a certain amount of energy in the form of heat, light, electricity is either absorbed or evolved. For example, when carbon bums, it reacts with oxygen to form carbon dioxide, and heat is liberated (given out). Carbon dioxide is a chemical compound, and its formation from the elements involve the evolution of heat.
Carbon + Oxygenà Carbon dioxide + Heat
