Class 6th Ch- Separation of Substances

 What is Separation?


• The removal of substances from a mixture of two or more substances is known as separation.

• Some examples of separation are:

→ Separating stones from rice
→ Churning milk to obtained butter

Why do we need to separate substances? 

→ To obtained two different components
→ To remove impurities or harmful components
→ To group substances of different sizes

Separation of substances

• Pure substance: The substance which contain only one type of particles.
Examples: Water

• Impure substances: The substance which contain more than one kind of particle.
Examples: A plate of rice is mixed with some stones.

Separation of components of mixtures

• Mixture of solid with solid

(i) Hand picking

→ The component of a solid-solid mixture can be separated by hand picking.

→ It is used for separating large size impurities like stones and husk.

→ For example: separating grass from mint leaves, separating pebbles from dal.

(ii) Threshing

→ The process in which the stalks are beaten to free the grain seeds.

→ Threshing is done with the help of bullocks. For large quantity of grains machines are used for threshing.

This method is used by the farmers to separate the grains from the stalks after harvesting.

(iii) Winnowing

→ It is process which is used to separate heavier and lighter components of a mixture by wind or by blowing air.

→ This method is used by farmers to separate lighter husk particles from heavier seeds of grain.

(iv) Sieving

→ It is a process in which a components of a mixture with different size can be separated by sieve.

→ The smaller particles remove out through the pore of sieve and the larger particle is left behind it.
This method is used to separate wheat bran (the bigger particles) from flour.
(v) Sublimation

→ The process in which the solid changes directly into gaseous state on heating is called sublimation.

Mixtures of solids with liquids

(i) Evaporation

→ It is a process which is used when we want to get back a substance that has been dissolved. In this process liquid changes into gaseous form on heating.

→ Example: Getting salt out of salty water.

(ii) Crystallization

→ It is a process which separates a pure solid in the form of crystals from a saturated solution.

Separation of solids that do not dissolve in liquids

(i) Sedimentation: The process of separation of 2 components in such a way that the heavier substance settles down
(ii) Decantation: separation of 2 components which do not mix together.
Example: Water and oil.

(iii) Filtration: The process in which separation of solid from liquid by the filter paper or strainer.
Example: separating mud from water by using filter paper.


• Condensation: It is a process by which a substance changes from the gas phase to liquid phase.

Can water dissolve any amount of a substance?

→ Water dissolves different amounts of soluble substances in it.

→ A saturated solution is one which cannot dissolve more of that substance.

→ To dissolves more of a substance in a solution we have to heating it. 

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