CBSE NOTES Class 9 Science Chapter-2. Is Matter around us Pure Methods of Separation of a mixture

2. Is Matter around us Pure?

The Separation of components of a Mixture:

Getting individual component from a mixture is known as separation. 

Importance of Separation: 

(i) Different methods of separation are used to get individual components from a mixture. 

(ii) Separation makes it possible to study and use the individual components of a mixture.

Common separating methods: 

(i) Filtration

(ii) Magnetic separation

(iii) Winnowing 

(iv) Decantation

(v) Sedimentation

(vi) Handpicking

(vii) Sieving 

Heterogeneous mixtures can be separated into their respective constituents by simple physical methods like handpicking, sieving, filtration that we use in our day-to-day life.

Sometimes special techniques have to be used for the separation of the components of a mixture.

There are many other important separating methods:

(1) Evaporation

(2) Centrifugation

(3) Seperating funnel

(4) Sublimation

(5) Crystallisation 

(6) Chromatography

(7) Distillation

(1) Evaporation: Liquid substances are heated to get vapourised and other remains particles obtained from mixture in this method. 

Applications: 

(a) Separating the volatile component (solvent) from its non-volatile solute by the method of evaporation.

(b) Obtaining coloured component (dye) from blue/black ink. 

(c) Obtaining salt from sea water. 

(2) Centrifugation : Sometimes the solid particles in a liquid 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.

Principle of Centrifugation: 

When it is rotated very fast the denser particles are forced to the bottom and the lighter particles stay at the top when spun rapidly.

Applications:

(a) Used in diagnostic 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.

(3) Separating funnel : It is used to separate a mixture of two immiscible (अघुलनशील) liquids, like oils and water. 

Principle of Separating funnel : The principle is that immiscible liquids separate out in layers depending on their densities.

Applications: 

(a) To separate mixture of oil and water.
(b) 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.

(4) Sublimation : In this method we use to separate such components of a mixture that have easily get sublimated, like ammonium chloride, camphor, naphthalene and anthracite.

Applications: 

(a) Salt from mixture of salt and ammonium chloride. 

(b) Iron fills from mixture of iron fills and camphor. 

(6) Chromatography : The method which is used to separates such solutes substances that are dissolved in only one kind of solvent. This method is known as chromatography. 

Principle of chromatography: The coloured component that is more soluble in water, rises faster and in this way the colours get separated.

Applications: 

(a) To separate colours in a dye. 

(b) To separate pigments from natural colours.

(c) To separate drugs from blood. 

(7) Distillation : This method is used to separate a mixture of two miscible (घुलनशील) liquids. This method is called distillation. 

It is used for the separation of components of a mixture containing two miscible liquids that boil without decomposition and have sufficient difference in their boiling points.

Applications: 

(a) Distillation is used in food industries for concentrating essencial oils, flavours and alcoholic beverages. 

(b) It is used in laboratory to seperates various miscible components of mixture. 

(c) Methenol or ethenol from water. 

(8) Fractional Distillation: 

To separate a mixture of two or more miscible liquids for which the difference in
boiling points is less than 25 K, fractional distillation process is used, for example, for the separation of different gases from air, different factions from petroleum products etc.

Fractionating Column: The apparatus is similar to that for simple distillation, except that a fractionating column is fitted in between the distillation flask and the condenser. A simple fractionating column is a tube packed with glass beads. The beads provide surface for the vapours to cool and condense repeatedly. 

Obtaining different gases from air: 

Air is a homogeneous mixture and can be separated into its components by fractional distillation. The air is compressed by increasing the pressure and is then cooled by decreasing the temperature to get liquid air. This liquid air is allowed to warm-up slowly in a fractional distillation column, where gases get separated at different heights depending upon their boiling points.

This process is as below: 

Air 

↓

Liquid air

↓

Obtaining oxygen, nitrogen, arogn and carbon dioxide on their boiling points

(9) Crystallisation : Crystallisation is a process that separates a pure solid in the form of its crystals from a solution.

The crystallisation method is used to purify solids. For example, the salt we get
from sea water can have many impurities in it. To remove these impurities, the process of crystallisation is used.

Applications:

(i) Purification of salt that we get from sea water.

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

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

Chemical properties: A chemical property of a substance that is observed when substance undergoes a chemical changes. Chemical properties cannot be determined by touching or viewing a sample of substance. 

Some chemical properties are as follows:

toxicity

flammability

heat of combustion

chemical stability

oxidation states

Differences between physical and chemical changes. 

Examples of physical changes: 

Cutting of trees, Making of chair or table, dissolving salt in water, Making of Salad from fruits etc. 

Examples of chemical changes: 

Digestion of foods, Cooking of foods, Rusting of Iron, changing colour of knife after cutting vegitables, buring of coal etc. 

Assignment : 

Q1. Which separation technique will you apply for the separation of the following? Write their name only.

(a) Ammonium chloride from a powdered mixture of sodium chloride and Ammonium chloride.

(b) Butter from cream.

(c) Oil from water. 

Q2. Write one property of colloids.

Q3. Write three differences between mixture and compound.

Q4. Classify into elements , compound and mixtures: sodium, Soil, Calcium carbonate, air.

Q5. Which of the following will show Tyndall effect:

(a) salt solution        

(b) milk

(c) starch                   

(d) copper sulphate solution

Q6. What is sublimation? Write the two substances that sublime.