Is Matter Around Us Pure? Class 9 Notes Science Chapter 2

Is matter around us pure ?

1. Introduction

We know that all the matter around us is not pure. If we observe some soil (Mitti) and some sugar placed on two different sheets of paper with a magnifying glass, we find soil contains clay particles, some grass particles and even some dead insects etc. That is soil contains particles of different kinds is called an impure substance
(or mixture). Now observe sugar which contains only one kind of particles is called a pure substance.

We can see that most of the matter around us exist as a mixture of two or more pure components, for example, milk, sea water, minerals etc. are all mixtures.

Type of matter :_

On the basis of chemical nature, matter can be classified into two types:

(i) Pure substance. (ii) Impure substance (mixture)

(i) Pure substance :_ A homogeneous material which contains particles of only one kind and has a definite set of properties, is called a pure substance. OR

A pure substance is a distinct type of matter that can not be separated into other types of matter by any physical process e.g. oxygen, sulphur, iron etc. are pure substance however, if a substance is composed of two or more different kinds of particles combined together in fixed proportion by weight, then the substance is also regarded as pure substance. e.g. Sodium chloride is a pure substance, because it has a fixed number of sodium and chloride ions, combined together in fixed proportion by weight. Similarly, magnesium oxide (MgO), carbon dioxide (CO₂), copper sulphate (CuSO₄) etc. are pure substances.

It does not imply all homogeneous substances for example, common salt solution in water, is a homogenous solution. Yet it cannot be called a pure substance, as it is made of two different substances e.g. salt and water.

(ii) Mixture :_ When two or more substances (elements, compounds or both) are mixed together in any proportion, such that they do not undergo any chemical change, but retain their individual characteristics the resulting product is called a mixture. e.g. Brass is a mixture of copper and zinc. Crude oil is a mixture of large number of different hydrocarbons.

Type of mixture :_ Depending upon the nature of components a mixtures can be divided into two types

(a) Heterogeneous mixture :_ A mixture is which different constituents are not mixed uniformly, is called a heterogeneous mixtures. The components of a heterogeneous mixture can be observed with naked eyes or with the help of a microscope. e.g. Sand and iron filings, sand & water etc.

(b) Homogeneous mixture :_ A mixture in which different constituents are mixed uniformly, is called a homogeneous mixture. Homogeneous mixtures are also known as solution. The components of such a mixture cannot be seen even under a microscope. e.g. salt solution, copper sulphate solution, sugar solution. Similarly alloys such as brass, bronze etc. are homogeneous solid solutions of metals.

Solutions :_ A homogeneous mixture of two or more substances is called a solution. In a solution there is homogeneity at the particle level. Usually we think of a solution as a liquid that contains either a solid or a liquid or a gas dissolved in it. However, this is not true. We can have a solid solution as in the case of Alloys.

e.g. Air is a mixture of gas in gas. Air is a homogeneous mixture of a number of gases. It's two main constituents of gases are oxygen (21%) and Nitrogen (78%)

Alloys :_ Alloys are homogeneous mixtures of metals and cannot be separated into their components by physical methods. But still, an alloy is considered as a mixture, because it shows the properties of it's constituents and can have variable composition. For example, brass is a mixture of 30% zinc and 70% copper.

Components of a solution :_ The substances present in a homogeneous solution, are called components of the solution. A solution basically has two components i.e. a solvent and a solute.

(a) Solvent :_ The component of a solution which dissolves the other component in it self, is called solvent. A solvent is the larger component of the solution. e.g. a solution of sugar in water is a solid in liquid solution. In this solution, sugar is the solute and water is the solvent.

(b) Solute :_The component of the solution which dissolves in the solvent, is called solute. Solute is the smaller component of the solution e.g. solution of iodine in alcohol known as 'tincture of iodine', iodine is the solute. Similarly, in carbonated drinks (Soda water), carbon dioxide gas is the solute.

Characteristics of a solution :_

· Solution is a homogeneous mixtures.

· The size of solute particles in a solution is extremely small. It is less than 1 nm in diamter.

· The particles of a solution cannot be seen even with a microscope.

· The particles of a solution pass through the filter paper. So, a solution cannot be separated by filtration.

· The solutions are very stable. The particles of solute present in a solution do not separate out on keeping.

· A true solution does not scatter light (because its particles are very small).

Concentration of a solution :_ The concentration of a solution is the amount of solute present in a given quantity of the solution. In other words the mass of the solute in grams, which is present in 100 g of a solution.

In a solution the relative proportion of the solute and solvent can be varied. Depending upon the amount of solute present in a solution, it can be called a dilute, concentrated or a saturated solution. Different substances in a given solvent have different solubilities at the same temperature.

The most common method for expressing the concentration of a solution, is called percentage method.

The concentration of solution refers to the percentage of solute present in the solution. The percentage of solute can be expressed in terms of -

(i) Concentration of a solution in terms of mass of solute :_ If the solution is of a 'solid solute' dissolved in a liquid, then we consider the 'mass percentage of solute' in calculating the concentration of soluton. So, in the case of a solid solute dissolved in a liquid solvent.

Mass by mass percentage of a solution = 

The mass of solution = mass of solute mass of solvent.

(ii) Concentration by mass by volume percentage of a soluiton.

Mass by volume percentage of a solute in - Solution = 

Depending upon the unit of the mass and volume, the mass by volume percentage of a solute in solution, can have following units.

(a) gram/ml (b) gram/litre

Saturated solution :_

A solution which at a given temperature dissolves as much solute as it is capable of dissolving, is
said to be a saturated solution.

Ex. At 30°C, 55 g of common salt dissolves in 100g of water. However, if more of common salt is added to the above solution, it just does not dissolve. In such a situation, the solution of common
salt containing 55 gm of salt in 100 gm of water, is a saturated solution at 30°C.If a saturated solution at some particular temperature is heated, the solution becomes unsaturated, because of the increase in solubility. If a saturated solution at some higher temperature is cooled, it remains saturated. The excess solute comes out of the solution and deposits it self in the form of crystals.

Unsaturated solution :_

When the amount of solute contained in a solution is less than the saturation level, the solution is said to be an unsaturated solution.

Ex. At 30°C, if 45 g of common salt is dissolved in 100 g of water, such solution so formed is capable of dissolving more of the common salt, then such a solution is called unsaturated solution.

Super saturated solution :_

A solution which contains more of the solute than required to make a saturated solution, is called a
super saturated solution.

Solubility of a solute :_ The amount of solute (in gram), which dissolve in 100 g of water (solvent), at a given temperature, is called solubility of the solute at that temperature.

Substance (or Solute) Solubility in water (at 20°C)

1. Copper sulphate 21 g

2. Potassium nitrate 32 g

3. Potassium chloride 34 g

4. Sodium chloride 36 g

5. Ammonium chloride 37 g

6. Sugar 204 g

Suspensions :_ A suspension is a heterogeneous mixture in which the small particles of a solid are spread throughout a liquid without dissolving in it. The particles have a tendency to settle down at the bottom of solvent and can be filtered out, because their size is bigger than the size of the pores of filter paper.

eg. (1) Chalk-water mixture is a suspension of fine chalk particles in water.

(2) Muddy water is a suspension of soil particles in water.

Properties of a suspension :

1. A suspension is a heterogeneous mixture.

2. The size of solute particles in a suspension is quite large. It is larger than 100nm in diameter.

3. The particles of a suspension can be seen easily.

4. A suspension scatters a beam of light passing through it, because it's particles are quite large.

5. The particles of suspension settle down, when the suspension is kept undisturbed.

6. The process of setting of suspended particles under the action of gravity is called sedimentation. So suspensions are unstable.

Colloidal solution or Colloids :

A heterogeneous solution in which the particle size is in between 10^_7cm to 10^_5cm such that the solute particles neither dissolve nor settle down in a solvent, is called colloidal solution. The components of a colloidal solutions are the dispersed phase and the dispersion medium. The solute-like component or the dispersed particles in a colloidal form of the dispersed phase, and the component in which the dispersed phase is suspended is known as the dispersing medium.

Properties of colloids :

1. The size of particles of a colloid is too small to be individually seen by naked eyes.

2. They do not settle down when left undisturbed, that is colloid is quite stable.

3. They can not be separated from the mixture by the process of filteration. But, special technique of separation known as centrifugation can be used to separate the colloidal particles.

4. Colloidal solutions are not transparent, but translucent in nature.

5. The particles of a colloidal solution scatter light i.e. when strong beam of light is passed through the colloidal solution, the path of beam becomes visible.

Dispersed phase :- It is the component which is present in small proportion and consists of particles of colloidal dimensions (10⁹ m to 10⁷ m).

Dispersion medium :- It is the component which is present in excess and acts as a medium in which colloidal particles are dispersed.

Common examples of colloids

Dispersed Phase Dispersing Medium Type Example

Liquid Gas Aerosol Fog, clouds, mist

Solid Gas Aerosol Smoke, Automobile Exhaust

Gas Liquid Foam Shaving cream

Liquid Liquid Emulsion Milk, face cream

Solid Liquid Sol Milk of magnesia, mud Gas Solid Foam Foam, rubber, sponge, pumice

Solid Solid Solid Sol Coloured gemstone, milky glass

Brownian movement of colloids :-

The colloidal particles are moving at random in a zigzag motion in all directions. This type of zig-zag motion of colloidal particles is called Brownian movement. This is shown figure. The brownian movement is caused by the collision (hitting) of

the colloidal particle with the molecules of the dispersion medium.

Tyndall effect :

The phenomenon due to which the path of light becomes visible, due to scattering of light by the colloidal particle is called Tyndall effect.

Example : Tyndall effect can also be observed when a fine beam of light enters a room through a small hole. This 
happens due to the scattering of light by the particles of dust and smoke in the air. Tyndall effect can be observed when sunlight passes through the canopy of a dense forest. In the forest mist contains tiny droplets of water, which act as particles of colloids dispersed in air.

Difference between true solutions and colloidal solutions :

Difference between colloidal solutions and suspensions :

Colloidal Solutions Suspension

Separating the components of a mixture :

Many of the material around us are mixtures, these mixtures have two or more than two constituents mixed in them. It may not be possible to use a mixture as such in homes and in industries. We may require only one or two separate constituents of a mixtures for our use. So, we have to separate the various mixtures into their individual constituents to make them useful in our daily life.

The various constituents of a mixture have different physical properties such as density, solubility, size of particles volatility, boiling points, etc.

Heterogeneous mixtures can be separated into their respective components by simple physical methods such as handpicking, sieving, filtration etc. in every day life. However, for separating homogeneous mixtures special techniques are employed depending upon the difference in one or more.

`Separation of coloured components (Dye) from Blue or Black ink :

The blue ink (or black ink) used in fountain pens is a liquid mixture. It is a mixture of a 'dye' in water. We can separate the 'coloured component (dye) by the process of evaporation. In process of separation we do not heat the china dish containing ink directly over the flame.This is because the 'dye' obtained from ink can get decomposed by the high temperature produced by the direct heating with a burner. We use a 'water bath' for evaporating ink.

Experiment to obtain coloured component (Dye) from ink :

We take a beaker and fill it half with water (as a water bath). About 5ml of ink (Blue ink or black ink) is put in a china dish. The china dish containing ink is then placed over the mouth of beaker containing water, which is kept on a tripod stand.

We now start heating the beaker with a burner, soon the water in beaker starts boiling to form steam, this steam heats the ink in the china dish. Due to this heating, the water present in ink starts evaporating gradually. When all the water has evaporated from ink . we stop heating. We will find that a small amount of a solid coloured material is left in the china dish. Thus we can separate the volatile component (Solvent) from its non-volatile solute by the method of evaporation.

Separation of Cream from milk :

Sometimes the solid particles in a liquids are very small and pass through a filter paper. for such particles the filtration technique cannot be used for separation. Such mixtures are separated by centrifugation.

Centrifugation :

The method of separating finely suspended particles in a liquid, by whirling the liquid at a very high speed is called centrifugation.

Principal of centrifugation : It is based on that when a very fine suspensions or a colloidal solution is whirled rapidly, the heavier particles are forced towards the bottom of liquid and the lighter stay at the top.

Method :

Milk is suspension of tiny droplets of oil cream in a water of liquids. The milk is put in a closed container in big centrifugation machine. When the centrifugation machine is switched on, the milk is rotated at a very high speed in its container. Due to this, the milk separates into 'cream' and 'skimmed milk'. The cream, being lighter, floates over the skimmed milk can then be removed. Thus, cream is separated from milk by centrifugation.

Application of centrifugation :

• It is employed in diagnostic Laboratories in testing urine and blood samples.
• It is employed in blood banks to separate different constituents of blood.
• It is used in drying machines to squeeze out water from the wet clothes.

Separation of a mixture of two immiscible liquids :

The separation of two immiscible liquids is based on the difference in their densities. The apparatus used for separation is separating funnel.

Methods :

The mixture of two immiscible liquids is put in a separating funnel and allowed to stand for some time. The mixtures separates into two layers according to the densities of the liquids in it.

Water and kerosene oil are two immiscible liquids. Pour the immiscible liquids mixture in the separating funnel. Allow the mixture to stand for half an hour or more. It forms two layers. Water being heavier, forms the lower layers in the separating funnel. Whereas kerosene, being lighter, forms the upper layer: on opening the stop-cock of separating funnel, the lower layer of water comes out first and collected in a beaker. When the water layer has completely run off, then the stop-cock is closed. The kerosene is left behind in the separating funnel. It can be removed in a separate breaker by opening the stop-cock again.

Application :

• To separate mixture of oil and water.
• In the extraction of iron from its ore, the lighter slag is removed from the top by this method to leave the molten iron at the bottom in the furnace.

Separation of a mixture of common salt and Ammonium Chloride :

This method is used in the separation of such solid-solid mixtures where one of the components sublimes on heating. However it is useful only if the components of the mixture do not react chemically on heating. So, we can separate ammonium chloride from a mixture of common salt and ammonium chloride by this process.

Methods :

The mixtures of common salt and ammonium chloride is taken in a china dish and placed on a tripod stand. The china dish is covered with an inverted glass funnel. A loose cotton plug is put in the upper, open end of the funnel to prevent the ammonium chloride vapours from escaping into the atmosphere. The china dish is heated by using a low Bunsen flame, on heating the mixture ammonium chloride changes into white vapour. These vapours rise up and get converted into solid ammonium chloride on coming in contact with the cold, inner walls of the funnel.

When the mixture gives off no more white fumes, lift the funnel, scrap the fine white powder from its sides on a piece of paper. This is pure ammonium chloride. The residue left behind in the funnel is sodium chloride. Some examples of solids which sublime are camphor, naphthalene and anthracene.

Chromatography :

The process of separation of different dissolved constituents of a mixture by adsorbing them over an appropriate adsorbent material is called, Chromomatography. Kroma in greek means colour. The adsorbent medium is generally magnesium oxide, alumina or filter paper.

There are many types of chromatography but the simplest form is the paper chromatography. This separation is based on the fact that the different constituents of a mixture get adsorbed differently on the same adsorbent material, because they have different rates of movement. The rate of movement of each adsorbed material depends upon.

The relative solubility of the constituent of mixture in a given solvent. The relative affinity of the constituents of mixture for the adsorbent medium. Paper chromatography is very useful in separating various constituents of coloured solutes present in a mixture lime, ink, dyes etc.

Separation of coloured constituents present in a mixtures of ink and water.

Method :

The different coloured dyes present in black ink can be separated by performing a paper chromatography.

• Take a thin and long strip of filter paper. Draw a pencil line on it, about 3 centimeters from one end.
• Put a small drop of black ink on the filter paper strip at the centre of the pencil line. Let the ink dry.
• When the drop of ink has dried, the filter paper strip is lowered into a tall glass jar containing water in its lower part (keeping the pencil line at the bottom). The filter paper strip is held vertically by attacking its upper end to a glass rod with cellotape (the glass rod being kept over mouth of glass jar). The lower end of the paper strip should dip in water but the pencil line should remains above the water level in the jar. 
• The water gradually rises up the filter paper strip by capillary action. As water moves up on the paper strip, it takes along the dyes present in ink. The dye which is more soluble in water dissolves first rises faster and produces a coloured spot on the paper at a higher position. The less soluble dyes dissolve a little later, rise slower and form coloured spots at lower heights. In this way, all the dyes present in black ink get separated.
• When the water reaches near the top end of the filter paper strip, the paper strip is removed from the jar and dried. The paper with its separate coloured spots is called a chromatogram.
• The chromatogram obtained by using black ink in this experiment has three coloured spots on it. This means that the given sample of black ink has three different dyes mixed in it.

Application :

To separate

1. Colours in a dye

2. Pigments from natural colours

3. Drugs from blood.

Separation of mixture of two miscible liquids :

Different types of fractionating column

Those liquids which mix together in all proportions and form a single layer, are called miscible liquids. Alcohol and water are miscible liquids because they mix together in all proportions and form a single layer on mixing.

To separate a mixture of two or more miscible liquids for which the difference in boiling points is less than 25K, fractional distillation process is used.

A simple fractionating column is a long vertical glass tube filled with glass beads. The glass beads provides a large surface area for hot vapours to cool and condense respectively.

Separate  a mixture of Ethylalcohol and water

Method :

Ethylalcohol and water are miscible liquids. The boiling point of ehtylalcohol is 78°C and the boiling point of water is 100°C, a mixture of ehtylalcohol and water can be separated by fractional distillation. The mixture of ehtylalcohol and water is heated in distillation flask fitted with a fractionating column. When the mixture is heated, both ehtylalcohol and water form vapours as their boiling points approach. The ehtylalcohol vapour and water vapour rise up in the fractionating column. The upper part of the fractionating column is cooler, so as the hot vapours rise up in the column, they get cooled, condense and trickle back into the distillation flask. As the experiment goes on, the fractionating column warms up by the heat released by the condensed vapours. After some time, a temperature at the top of column being much less than at its bottom. When the temperature at the top of the fractionating column reaches 78°C, then ehtylalcohol vapour passes into the condenser, gets cooled and collects in a beaker kept at the end of the condenser. The ehtylalcohol water mixture is kept boiling at such a rate that the thermometer shows the boiling points of ehtylalcohol (78°C). In this way, all the ehtylalcohol distills over and gets separated.

Separation of the Gases of the air :

Air is a mixture of gases like nitrogen, oxygen, argon, carbon dioxide, helium, neon etc. The major component of air is nitrogen (78.03%). The second major component of air is oxygen (20.99%) and the third major component of air is argon (0.93%).

All these gases are obtained from air on a large scale. This is because air is the cheapest source of these gases.

Air is a homogeneous mixture and can be separated into its components by fractional distillation of liquid air.

Methods :

• The air is first filtered to remove dust, then water vapour and carbon dioxide are removed. If water vapour and carbon dioxide are not removed, they would become solid in the cooling process and block the pipes.
• Air is compressed to a high pressure and then cooled. This cooled air is then allowed to expand quickly into a chamber through a jet. This expansion cools the air even more.
• The process of compression, cooling and rapid expansion of air is repeated again and again makes the air more and more cool. Ultimately the air gets so cooled that it turns into a liquid. In this way, liquid air is obtained.

• The liquid air is fed into a tall fractional distillation column from near its bottom and warmed up slowly.
  • Liquid nitrogen which present in air, has the lowest boiling point, of , _ 196°C. So, on warming, liquid nitrogen boils off first to form nitrogen gas.
  • Liquid argon which present in liquid air has a slightly higher boiling point of , _186°C, so liquid argon boils off next and collected as argon gas in the middle part of the fractional distillation column.
  • Liquid oxygen also present in liquid air has a still higher boiling point of, _ 183°C. so, liquid oxygen boils off last and collected as oxygen gas from the bottom of the fractional distillation column.

Separation of pure copper sulphate from impure sample :

The process involved in obtaining pure copper sulphate from its impure sample, is crystallisation.

Crystallisation :

The process of cooling a hot, concentrated solution of a substance to obtain crystals is called crystallisation. Crystallisation is a process that separates a pure solid in the form of its cyrstals from a solution.

Methods :

1. We take about 10 grams of impure copper sulphate and dissolve it in minimum amount of water in a china dish to make copper sulphate solution.
2. Filter the copper sulphate solution to remove insoluble impurities.
3. Heat the copper sulphate solution gently on a water bath to evaporate water and obtain a saturated solution. This can be tested by dipping a glass rod in hot solution from time to time. When small crystals form on the glass rod, the solution is saturated. Then stop heating.
4. Allow the hot, saturated solution of copper sulphate to cool slowly.
5. Crystals of pure copper sulphates are formed, impurities remains behind in the solution.
6. Separate the copper sulphate crystals from solution by filtration and dry.
7. Crystallisation is a better technique than evaporation to dryness because of following reasons.
   •  Some solids decompose or get charred on heating to dryness during evaporation.
   •  The soluble impurities do not get removed in the process of evaporation. But such impurities get removed in crystallisation.

Application :

1. Purification of salt that we get from sea water

2. Separation of crystals of alum (phitkari) from impure samples.

Supply of drinking water in a city :

In cities, drinking water is supplied from water works. In water works, the methods like sedimentation , decantation, loading, filtration and chlorination etc are used to remove undesirable materials from water. The source of water supply in a city is either a nearby river or a lake called reservoir. The river water and lake water usually contain suspended solid substances and some germs, so, before this water can be supplied to homes, it must be purified to remove suspended impurities as well as germs.

The purification of river water or lake water is done in the following steps.

(1) Sedimentation : The water is allowed to stand in big tanks, where heavier suspended impurities settle down. To increase the rate of sedimentation, alum is added to it. The impurities settle at the bottom.

(2) Filtration : The semi-clear water is allowed to pass through beds of sand, charcoal and gravel to remove suspended impurities.

(3) Removal of harmful - organism or sterilisation : The harmful bacteria in filtered water can cause very serious diseases such as typhoid, cholera etc. Thus, to the filtered water bleaching powder or chlorine gas is added. This kills the micro-organism and hence the water becomes fit for drinking. This water is directly pupmed into overhead tanks for supply to a city.

Physical and chemical changes :

There are some changes during which no new substances are formed. On the other hand, there are some other changes during which new substances are formed. So, on the basis of whether new substances are formed or not, we can classify all the changes into two groups. Physical changes and chemical changes.

Physical Properties : The properties that can be observed and specified like colour, hardness, rigidity, fluidity, density, melting point, boiling point etc. are the physical properties.

Physical changes : Those changes in which no new substances are formed, are called physical changes. In a physical change the substances involved do not change their identity. They can be easily returned to their original form by some physical process. This means that physical changes can be easily reversed to form the original substance. The changes in physical state, size and shape of a substances are called physical changes.

Example : When ice is heated it melts to form water. Though ice and water look different, they are both made of water molecules. Thus no new chemical substance is formed during the melting of ice. So, the melting of ice to form water is a physical change. When water is cooled, then water solidifies to form ice. This is called freezing of water. The freezing of water to form ice is also a physical change. Some other example of physical changes are : Boiling of water, condensation of steam, ringing of an electric bell and breaking of a glass.

Chemical changes : Those changes in which new substances are formed, are called chemical changes. A chemical change is also called a chemical reaction. In a chemical change, the substances involved, change their identity . They get converted into entirely new substances. The new substances usually cannot be returned to their original form. This means that chemical changes are usually irreversible.

Example : When a magnesium wire is heated it burns in air to form a white powder called 'magnesium oxide'. This magnesium oxide is an entirely new substance. Thus a new chemical substance is formed during the burning of a magnesium wire is a chemical change. Some other examples of chemical changes are : Burning of candle, Burning of character, and burning of hydrogen in oxygen to form water.

 Differences between Physical and Chemical Changes :

Types of pure substances :

On the basis of their chemical composition, substances can be classified either as elements or compounds.

Elements :

Robert Boyle was the first scientist to use the term element is 1661. Elements are the basic building block of matter, every substances on the earth made from one or more elements. There are 115 elements discovered so far, amongst these elements , 92 elements occur in nature, whereas 23 have been made in nuclear laboratories, majority of the element are solid. Eleven elements are in gaseous state at room temperature. Two elements are liquid at room temperature -mercury and bromine. Antoine Laurent Lavoiser (1743-94). A french chemist, defined an element as a basic form of matter that can not be broken down into simpler substances by chemical reactions. Element also can be defined as a substance made up of the atoms with same atomic number.

Example :

Elements can be classified as metals, non-metals and metalloids. eg. hydrogen, oxygen, nitrogen , zinc, mercury etc. Metals usually show some or all of the following properties.

Metalloids : Some element have intermediate properties of the metals and non-metals. The elements which exhibit the properties of metals as well as non-metals, are called metalloids.

Example : Boron, Silicon, Germanium etc.

Compounds : A pure substance, which is composed by two or more elements, combined chemically in a definite ratio, such that it can be broken into elements only by chemical means, is called compound.

Explain :-

The two or more elements present in a compound, are called constituents or components of the compound, for example, water is a compound of hydrogen and oxygen, combine together in the ratio of 1 : 8 by weight. The water can be broken into its consitituents only by electro-chemical method i.e. by passing electric current through it. The compounds can be further classified as acids, bases and salts.

The product formed by mixing 1 g of sulphur powder and 2g of iron filings / turnings called a mixture.

• The constituents of product i.e. iron fillings and yellow particles of sulphur can be seen with naked eye, which is the property of a mixtrue.
• The iron fillings can be separated by dissolving the mixture in carbon disulphide, sulphur dissolves, but not the iron. As the constituents can be separated by physical means therefore the product is a mixture.
• The constituents iron and sulphur are not evenly spread. At some places iron filings are more than sulphur.
• No energy is absorbed when the sulphur powder is mixed with iron filings.
• The particles of iron and sulphur retains individual chemical and physical properties.

The product formed on heating 1g of sulphur powder and 2g of iron turnings called a compound.

• The product formed is iron sulphide the yellow particles of sulphur and fillings of iron are no longer visible.
• The iron or sulphur cannot be separated from the iron sulphide by any physical means.
• The composition of iron sulphide is same throughout.
• Heat energy is evolved when the iron reacts with sulphur. The product continues glowing with red dull colour, even when the heating is stopped.
• The properties of the product (iron sulphide) are entirely different from the properties of iron and sulphur.

Difference between mixtures and compounds :