CLASS 9
Separating the components of a mixture 

The components of a heterogeneous mixture can be separated by simple methods like hand picking, sieving, filtration etc.

   Sometimes special techniques are used to separate the components of mixtures like :-

   i) Evaporation

  ii) Centrifugation

 iii) Decantation (Using separating funnel) 

 iv) Sublimation

  v) Centrifugation

 vi) Chromatography

vii) Distillation and fractional distillation

centrifugation

The method of separating denser particles and lighter particles from a mixture by using a centrifuging machine

is called centrifugation.

    Eg :- If we take some milk in a centrifuging machine and spin it rapidly, the cream separates from the milk because cream is less dense than milk.

 DECANTATION USING SEPARATING FUNNEL

This method is used for separating a mixture of immiscible liquids. Liquids separate into different layers depending on their densities.

     Eg :- If we take a mixture of kerosene oil and water in a separating funnel, it forms separate layers of oil and water. The water can be separated by opening the stop cock. After the water flows out the stop clock can be closed.

SUBLIMATION

This method is used to separate a mixture of a sublimable component from a  component  that does not sublimateby heating the mixture.

    Eg :- If a mixture of ammonium chloride and common salt is heated, the ammonium chloride sublimes and can be cooled and solidified and collected and salt is left behind

CHROMATOGRAPHY

This method is used for separating coloured components from a liquid by using a filter paper or blotting paper.

   Eg :- Put a drop of ink near one end of a strip of filter paper and dip the end of the paper in a test tube containing water. Ink is a mixture of two or more coloured components. The component which is more soluble in water rises faster and get separated.

DISTILLATION

 This method is used for separating a mixture of miscible liquids by boiling the mixture and cooling and condensing the vapours.

     Simple distillation :- is used for separating a mixture of two miscible liquids having sufficient difference in their boiling points.

     Eg :- If a mixture of acetone and water is heated in a distillation apparatus, the acetone which has a lower boiling point than water first boils and cools and condenses and is separated from the water

Fractional distillation :- is used for separating a mixture of two or more miscible liquids whose difference in boiling points is less than 25K.

    The apparatus used for fractional distillation is similar to that used for simple distillation except that a fractionating column is fitted between the distillation flask and condenser. The fractionating column has glass beads which increases the surface for the vapours to cool and condense.

    Fractional distillation is used for separating the components of petroleum, separating the different gases from air etc.

Separation of components of air

Air is a mixture of gases. The components of air can be separated by fractional distillation.

   Air is compressed by increasing the pressure and cooled by decreasing the temperature to get liquid air. The liquid air is then allowed to warm up slowly in a fractional distillation column. Then the different components separate at different heights depending on their different boiling points.

flow chart from the book

PURIFICATION OF SOLIDS BY CRYSTALLISATION

Crystallisation is the process of obtaining a pure solid in the form of crystals from its solution.

     Eg :- By crystallisation we can obtain pure copper sulphate from its solution.

     Dissolve about 5g of copper sulphate in minimum amount of water. Filter the solution to remove the impurities. Evaporate the solution in a china dish to get a saturated solution. Cover the solution with a filter paper and alllow it to cool. Pure copper sulphate crystals are formed.

TYPES OF PURE SUBSTANCES

         Pure substances are of two types. They are elements and

     compounds.

 i) Element :- is a basic form of matter which cannot be broken down

    into simpler substances by chemical reactions. Elements are of 

    three types. They are metals, non metals and  metalloids.  

   Properties of metals :-

   They have lustre. They are malleable and ductile. They are good

   conductors of heat and electricity. They are sonorous.

   Eg :- iron, aluminium, zinc, mercury, copper, silver, gold etc.

   Properties of non metals :-

   They do not have lustre. They are not malleable or ductile. They are 

   poor conductors of heat and electricity. They are not sonorus.

   Eg :- hydrogen, oxygen, nitrogen, iodine, carbon, sulphur,

   phosphorus etc.

   Properties of metalloids :-  

   Metalloids are elements which show some properties of metals and

   some properties of non metals.

   Eg :- boron, silicon, germanium etc.

(ii) COMPOUNDS