6th Chp 5 Notes

             Class 6th Science Notes        

     Chapter 5 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.