Notes of chapter: Is Matter Around us Pure? are presented below. Indepth notes along with worksheets and NCERT Solutions for Class 9.
Matter can be divided in two categories-, ie, pure substances and mixtures.
(2) Pure substances –
When all the particles of the matter are of same chemical nature, is called pure substance or pure matter.
Pure substances can be classified in two types –
Elements are first defined on the basis of experiments by French chemist, Antoine Laurent Lavoisier. Element is a basic form of the matter that can not be broken in to simpler substances by chemical reaction.
Robert Boyle was the first scientist to use the term elements.
Elements are divided in to three types–
(b) Non – metals
(c) Metalloids are those elements which have properties of metals and non –metals.
Eg:- silicon, boron, germanium etc.
Facts about elements are listed below-
(a) They are more than 100 in numbers. (2 elements are naturally occurring and the rest are man –made.
(b) Most of the elements are solid.
(c) 11 elements are in gaseous state at room temperature.
(d) Mercury and bromine are found liquid at room temperature.
(e) Elements, gallium and cesium become liquid at a temperature slightly above room temperature (303K).
The pure substances composed of two or more elements which are chemically combined with one another in a fixed are known as compound.
Eg:- Water, methane, sugar etc.
When two or more pure substances mix in any proportion is called mixture. Mixture can be separated in pure substances by separation techniques.
Eg:- Mixture of sodium chloride in water
Types of Mixture –
When a mixture has uniform composition of substances throughout, is called as homogeneous mixture.
Eg:- Salt in water – we get throughout same composition of water and salt.
When a mixture has non – uniform composition of substances, is called as heterogeneous mixture.
Eg:- Mixture of iron fillings or nails and water – Iron fillings or nails are not mixing with water uniformly, they set at the bottom of the beaker.
Oil and water – oil always find at the surface of water.
Solution is a homogeneous mixture of two or more substances.
Eg:- Lemonade tastes same in every sip.
(i) Components of the solution-
The substance which dissolves the other substances is called solvent.
Eg: – In lemonade, water is solvent which dissolves lemon juice.
The substance which dissolved in solution is called solute.
Eg:- In lemonade, lemon juice is solute which dissolved in water(solvent).
(ii) Types of solution-
(a) Solid solution or alloys-
When two or more metals or a metal and a non – metal are making mixture and can not be separated by any physical method, the mixture is called solid solution or alloys. The mixture shows all properties of its constituents.
Eg: – Brass is a mixture of zinc and copper.
When two or more solid or liquid or gas dissolve sin liquid and have same constituent through out is called liquid solution.
Eg: – Lemonade- Homogeneous mixture of lemon and water
Sweet lemonades – homogeneous mixture of lemon, water and sugar
(c) Gaseous mixture-
When two or more gasses make a homogeneous mixture is called a gaseous mixture.
(iii) Properties of solution-
(a) A solution is a homogeneous mixture.
Eg:- Lemonade, sugar solution
(b) The particles of a solution have size smaller than 1 nm(10-9 metres) in diameter. Therefore, we cannot see them by naked eyes.
(c)The path of light can not be seen by very small size of particles of solution.
(d) The particles of solution can not be filtered.
(e) The solution is stable.
(iv)Concentration of the solution-
The amount of solute in per unit volume or per unit mass of the solution is called concentration of the solution.
(a) The amount of the solute present in the saturated solution at particular temperature is known as solubility.
(b) A solution in which the maximum amount of the solute is dissolved in solvent at a particular temperature is known as saturated solution.
(c) A solution in which the amount of the solute is dissolved in solvent below the saturated level is known as unsaturated solution.
(d) Concentrated solution is the solution which has large quantity of solute in solution in comparison of solvent.
Concentration of the solution can be increase by increasing temperature of the solution.
(e) Dilute solution is the solution which has less amount of solute in solvent.
Formula to calculate concentration of solution –
Suspension is a heterogeneous mixture in which solute particles do not dissolve in solvent and remain suspended in the solution.
Eg:- Chalk in water
(i)Properties of the suspension-
(a) It is a heterogeneous mixture.
(b) The solute particles of the suspensions can be seen by naked eyes.
(c) The particles of suspension make its path visible by scattering light passing through it.
(d) A suspension is unstable (suspension settle down when left undisturbed). Therefore, they can be separated by the filtration. When particles of suspension settle down they can not scatter light.
A heterogeneous mixture of very small particles which cannot be seen by naked eyes but particles can scatter light beam easily, is called colloidal solution.
Eg:- Milk, jelly, smoke etc.
(i) Components of the colloidal solution-
(a) Dispersed phase are the solute of the colloidal solution.
(b) Dispersed medium are the solvent of the colloidal solution.
Common examples of colloids are tabulated below –
|Dispersed phase||Dispersed medium||Type||Example|
|Liquid||Gas||Aerosol||Fog, clouds, mist|
|Solid||Gas||Aerosol||Smoke, automobile exhaust|
|Liquid||Liquid||Emulsion||Milk, face cream|
|Solid||Liquid||Sol||Milk of magnesia, mud|
|Gas||Solid||Foam||Foam, rubber, sponge, pumice|
|Liquid||Solid||Gel||Jelly, cheese, butter|
|Solid||solid||Solid sol||Coloured gemstone, milky glass|
(ii)Tyndall effect –
When a beam of light passes through a hole and scattered by dust and smoke of the air (colloidal), the phenomenon is called tyndall effect.
Eg:- When beam of sunlight passes through the canopy of a dense forest, scattered by tiny droplets of water(mist) which act as colloid.
(iii) Properties of the colloid-
(a) It is a heterogeneous mixture.
(b) The size of the particles is two small that can not be seen by naked eyes but they are big enough to scatter a beam of light and make its path visible.
(c)They do not settle down. Therefore it is very stable.
(d) Colloids can not be separated by filtration but centrifugation can be used to separate the particles of colloid.
(7) Separation of components of mixture-
(i) By evaporation – Evaporation is a simple method in which we can separate solid from solid or liquid.
Eg:- Dye can be obtained from ink.
Put some ink on watch glass. Keep this dish on a beaker of filled with half water. Heat this beaker. After some time, evaporation will start. Water of ink will evaporate and we will get dye on watch glass.
Results from experiment –
(a) Water has evaporated from watch glass.
(b) Dye is found after evaporation on watch glass.
(c) Ink is a mixture of water and colour.
(ii) By centrifugation-
When centrifugation force is applied on mixture the denser particles settled down and lighter particles came up is called centrifugation process.
Centrifugation process is used when particles of mixture can not be filtered.
Eg:- Take full cream and use centrifugation machine to apply centrifugation force on it. After some time cream will come up and skimmed milk will settle down. We can do this experiment at home by using milk churner.
Results from experiment-
(a) After churning the milk, cream came up and skimmed milk settle down.
(b) Milk spun at high speed in centrifugation machine. The cream being lighter came up or float on the heavier particles of skimmed milk.
Applications of centrifugation –
(a) Used in laboratories for blood and urine tests.
(b) Used in dairies and home to separate butter from cream.
(c) Used in washing machines to squeeze out water from wet clothes.
(iii) By separating funnel-
Immiscible liquids can be separate by separating funnel by using property of their density.
Eg:- Take a separating funnel and fill it with water and oil. Let it stand undisturbed. After some time open up the stop cock of funnel and take out water from the mixture of oil and water. Close the stop cock, oil is inside the separating funnel which can be collected in different jar.
(a) To separate kerosene and water.
(b) In the extraction of iron from its ore.
(iv)By sublimation –
We can separate a mixture which contains sublimable particles by using property of sublimation of the particles.
Eg:- Take salt and camphor in a china dish. Cover this dish with funnel and put cotton the funnel mouth. Heat the arrangement. After some time camphor evaporated directly and collected on the walls of funnel as vapour. Salt left in china dish.
(v) Chromatography –
The technique used for the separation of those solutes that dissolves in the same solvent is known as chromatography.
Eg:- Place a drop of black ink on the line drawn on filter paper. Now keep this paper in a beaker with little water. Water level should be below the line on filter paper. After some time water raises on filter paper and water soluble colour of black ink rises faster and we can separate colour of black ink.
Results from experiments-
(a) The different colour of black ink raises as water rises on the filter paper.
(b) Yes, we obtain different colours on the filter paper strip.
(c) The black ink is a mixture of two or more water solubale colours. When water raises on the strip, colour of black ink soluble in water and get separated.
(a) colours in a dye.
(b) pigments from natural colours.
(c) drugs from abroad.
(vi) By distillation –
Distillation is a method in which a mixture of miscible liquids that boil without decomposition and have sufficient difference in their boiling points separated in its components.
Eg:- Take the mixture of acetone and water in a distillation flask. Fit a thermometer in the apparatus (shown in figure). Heat the mixture and check temperature from thermometer. After some time acetone vaporizes and condenses and collected from the condenser outlet. Water is left behind in the distillation flask.
(vii)By fractional distillation –
Fractional distillation can be done when miscible liquids have difference in boiling point is less than 256 k.
Eg:- Separation of different gases from air, different fractions from petroleum.
A simple fractioning column is a tube packed with glass beads. The beads are used to cool and condense the vapours. The process of fractional distillation of the gases are explained in flow diagram below-
(viii) Separation of gases from air by fractional distillation –
First, air is compressed and cooled by increasing pressure and decreasing temperature to change in to liquid air. This liquid air is then allowed to warm up in fractional distillation column and gases get separated at different heights.
The flow diagram below clears every step of separation of gases from air by fractional distillation –
(viii) By crystallisation –
Crystallisation is a process in which pure solid separates from a solution in the form of its crystal.
Eg:- Impurities of salt from sea water can be remove by crystallization process.