Question

Class 9th
science chapter 2
Give the short notes of methods of separation of mixtures​

Answer 1

Answer:

(1) Evaporation:

Evaporation is a process which is used to separate a solid substance dissolved in liquid. It is based on the fact that liquids vaporize easily whereas solids do not.

seperation by evaporation

Applications of Evaporation:

Obtaining salt from see water.

(2) Centrifugation:

It is a method of separating the suspended particles of a substance from a liquid in which the mixture is rotated at high speed in a centrifuge.

This method is useful in case the suspended particles in a liquid are too small too be retained by filter paper.

seperation by centrifugation

Principle of Centrifugation:

When a mixture is rotated very fast, the denser particles are forced to go to the bottom of the centrifuge and the lighter particles stay at the top.

Applications of Centrifugation:

Used in dairies to separate cream from milk.

Used in washing machines to squeeze out water from wet clothes.

(3) Separating funnel

It is used to separate a mixture of two immiscible liquids, like oil and water.

seperation by seperating funnel

Principle of Separating funnel :

When a mixture of two immiscible liquids is kept in a separating funnel, the liquids separate out in layers depending on their densities with the heavier forming the top layer.

Applications of Separating funnel:

To separate mixture of oil and water.

In the extraction of iron from its ore where the lighter slag (molten waste material) is removed from the top by to leave the molten iron at the bottom of the blast furnace.

(4) Sublimation:

This method is used to separate those components from a mixture which can sublime on heating.

For example: Ammonium chloride, camphor, naphthalene etc, can be separated from their mixture by sublimation

seperation by sublimation

Applications of Sublimation:

Iron can be separated from a mixture of iron fillings and camphor (volatile).

Common salt can be separated from a mixture of salt and ammonium chloride (volatile).

(5) Chromatography

This method is used to separate two or more dissolved solids which are present in a solution in very small quantities.

seperation by chromatography

Principle of Chromatography:

This method of separation is based on the fact that though two substances are dissolved in the same solvent but their solubilities can be different. The component which is more soluble in, rises faster and gets separated from the mixture.

Applications of Chromatography:

To separate colours in a dye by paper chromatography.

To separate drugs from blood.

(6) Distillation:

This method is used to separate a mixture solid in a liquid. It is the process of heating the liquid to form vapour, and then cooling the vapour to get back liquid.

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.

seperation by distillation

Principle of Distillation:

The volatile liquid evaporates on heating which can be recovered by cooling its vapours by the process of condensation.

Applications of Distillation:

It is used to remove salt from sea water to obtain drinking water.

(7) Fractional distillation

It is the process of separating two or more miscible liquids by distillation, the distillate being collected in fractions due to boiling at different temperatures.

sepeartion by fractional distillation

Fractionating Column:

The apparatus used in this process is similar to that for simple distillation except a fractionating column which is fitted in between the distillation flask and the condenser. A simple fractionating colunrn is a tube packed with glass beads. The beads provide surface for the vapours to cool and condense repeatedly.

Principle of Fractional Distillation:

In a mixture of two or more miscible liquids, the separation of various liquids depends on their boilibg points. The liquid having lower boiling point boils first and can be obtained first from the fractionating column than the liquid having higher boiling point.

Applications of Fractional Distillation:

It is used to separate a mixture of miscible liquids like alcohol-water mixture.

It is used to separate cruid oil ‘petroleum’ into useful fractions like kerosene, petrol, diesel, etc.

It is used to separate different gases of the air by taking the liquid air.

(8) Crystallisation :

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

Applications of Crystallisation:

Answer 2

Answer:-

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☛ Some commonly used methods are:-

• Explanation of some methods:-

1. Handpicking:- In the method of hand picking we used to pick up the slightly large particles undesirable particles from the grains by hands.
2. Threshing:- After, the crop is harvested, grains are seperated by threshing the plants on a stone or by making cattle walk over the crop. These days, machines called threshers are also used for this purpose. There are also machines called combines which can do both harvesting and threshing.
3. Winnowing:- The grains collected after threshing have some chaff which needs to be seperated. This is achieved by winnowing. It is the process where grains are dropped from a height. The heavier grains fall directly to the ground, while the lighter chaff blows away and collects at a distance.

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