Science class 6 – Chapter 5 – Separation of Substances – NCERT Exercise Solution (Question-Answer)

Q1. Why do we need to separate different components of a mixture? Give two examples.

Solution: Two or more substances are mixed together to form a mixture. Components of a mixture should be separated because the non-useful substance is mixed with useful substance. They may harm and spoil the useful substance.

Q2. What is winnowing? Where is it used?

Solution: Winnowing is the method of separating the components from a mixture.

Winnowing is used to separate heavier and lighter components of a mixture by wind or by blowing air. Farmers use this method to separate lighter husk particles from the heavier seeds of grains.

Q3. How will you separate husk or dirt particles from a given sample of pulses before cooking?

Solution: Husk and dirt particles are separated from pulses by handpicking method of separation.

Q4. What is sieving? Where is it used?

Solution: Sieving is the method of separation.

In this method fine particles are sieved through holes of the sieve while the bigger impurities remain on the sieve.

Sieving is used in flour mill to separate impurities like husk, stalk and stones that may still remain with wheat after threshing and winnowing.

When the component of the mixture has a difference in size, we use the sieving method to separate.

Q5. How will you separate sand and water from their mixture?

Solution: Sand and water are separated from their mixture by the method of sedimentation and decantation.

We take a mixture of sand and water in a glass. We know sand is heavier than water.

So, leave the glass (containing the mixture of sand and water) for half an hour. After that, we observe that sand settles at the bottom of the water.

Now, slightly tilt the glass without disturbing the water. Let the water move from the top flow into another glass. 

So, the component from the top layer (water) can be separated.

Q6. Is it possible to separate sugar mixed with wheat flour? If yes, how will you do it?

Solution: Yes, it is possible to separate sugar mixed with wheat flour by the following method:

a) Add the mixture of sugar and wheat flour in water.

b) Stir the solution to allow sugar to dissolve because sugar can dissolve in water.

c) Now, filter the mixture.

d) Filtrate contains sugar solution and residue will be wheat flour.

Q7. How would you obtain clear water from a sample of muddy water?

Solution: The following process should be carried out to obtain clear water from muddy water-

a) Take a mixture of muddy water in a glass.

b) Leave the glass (of mixture) for half an hour.

c) After that we observe that mud is settled at the bottom of water.

d) Now, slightly tilt the glass without disturbing the water.

e) Let the water move from the top-flow into another glass. 

Q8. Fill up the blanks

(a) The method of separating seeds of paddy from its stalks is called ___________.

Solution: threshing

(b) When milk, cooled after boiling, is poured onto a piece of cloth the cream (malai) is left behind on it. This process of separating cream from milk is an example of ___________.

Solution: filtration.

(c) Salt is obtained from seawater by the process of ___________.

Solution: evaporation.

(d) Impurities settled at the bottom when muddy water was kept overnight in a bucket. The clear water was then poured off from the top. The process of separation used in this example is called ___________.

Solution: decantation.

Q9. True or false?

(a) A mixture of milk and water can be separated by filtration.

Solution: False

(b) A mixture of powdered salt and sugar can be separated by the process of winnowing

Solution: False

(c) Separation of sugar from tea can be done with filtration.

Solution: False

(d) Grain and husk can be separated with the process of decantation.

Solution: False

Q10. Lemonade is prepared by mixing lemon juice and sugar in water. You wish to add ice to cool it. Should you add ice to the lemonade before or after dissolving sugar? In which case would it be possible to dissolve more sugar?

Solution: Ice should be added to sugar after dissolving sugar.

It is possible to add more sugar before adding ice.