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Class 6 NCERT Solutions Science Chapter 3 - Separation of Substances

Separation of Substances Exercise 29

Solution 1

We need to separate different components of a mixture:
a.To separate two different but useful components.
b.To remove non useful components.
c.To remove impurities or harmful components.

i.Through winnowing, we can separate grain from husk.
ii.Through evaporation, salt can be obtained from sea water.

Concept insight: Mixtures are separated to obtain individual components.

Solution 2

Winnowing is a physical method of separation. It is used to separate heavier and lighter components of a mixture by wind. It is used by farmers to separate lighter husk particles from heavier seed grains.

Concept insight: When a mixture is made to fall down from a height due to wind, lighter particles fall far away and heavier particles fall near the winnowing platform. It is used to separate husk from wheat grains.

Solution 3

To separate husk, winnowing is done. To separate dirt from pulses, we will add water to them. Dirt will get dissolved in water, husk being lighter will float on water and pulse grain will settle down.

Then, water with impurities can be removed by decantation.

Concept insight: Husk being light in weight can removed by winnowing and dust is soluble in water so, it can be separated by decantation.

Solution 4

Sieving is a process through which dirt impurities and bran present in grains and pulses are removed with the help of sieve. It is used at home, in flour mills and at construction sites.

Concept insight: Stones and bran cannot be separated by sedimentation or winnowing so, they are separated by sieving.

Solution 5

We can separate a mixture of sand and water by:
i.Sedimentation and decantation.

Concept insight: Sand is insoluble in water and being heavy, it settles down in the beaker thus, it can be separated by sedimentation and decantation. Also sand particles are big so they do not pass through a cotton cloth hence, sand and water can also be separated by filtration.

Solution 6

Yes. It is possible to separate a mixture of sugar and wheat flour. This can be done by the process of sieving. If the mixture of sugar and wheat flour is allowed to pass through a sieve, then the fine wheat flour particles would pass through the sieve, the sugar particles would be retained by the sieve.

Solution 7

Clear water can be obtained from a sample of muddy water by the method of filtration. In this method, the sample of muddy water is passed through a cloth having fine pores or through a filter paper. Clear water will pass through the filtering medium, leaving behind the mud.

Solution 8

(a) Threshing.

Concept insight: It is very difficult to take out each grain from the stalks so stalks are beaten to free the seeds. This process is called threshing.

 (b) Filtration. 

Concept insight: Cream particles being bigger do not pass through cloth.

(c) Evaporation.

Concept insight: Conversion of water into water vapour below its boiling point is called evaporation.

(d) Sedimentation and Decantation

Concept insight: Soil particles being heavy settle at the bottom of the container. After that, clear liquid can be removed by decantation.

Solution 9

(a) False. 

Concept insight: No, because both are liquids.

 (b) False.

Concept insight: Winnowing is used to separate a mixture of solids of which one is light weight and other is heavy weight.

(c) False. 

Concept insight: No, filtration can not be used to separate dissolved substances. 

(d) False.

Concept insight: Decantation is used to separate a mixture of insoluble solid in liquid.

Separation of Substances Exercise 30

Solution 10

We should add ice after dissolving sugar because the dissolving power of water decreases with decrease in temperature. So, if we add ice before dissolving sugar, less amount of sugar will get dissolved.

Concept insight: Dissolving power of water increases with temperature and vice versa.

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