NCERT Solutions for Class 6 Science Chapter 5 Separation of Substances

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

Answer: Separation is required to remove unnecessary components from useful components from the mixture. Also, separation is necessary to extract different useful components from the mixture. Following are the examples of separation:

1. Separation of stones and other impurities from food grains
2. Separation of tea leaves while straining tea.

2. What is winnowing? Where is it used?

Answer: Winnowing is the process of separating heavier particles from lighter particles with the help of wind or blowing wind. In general, this method is used by farmers to remove husk from grain.

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

Answer: Husk or dirt particles can be separated from pulses, by the method of sieving and sedimentation. Dirt particles are smaller in size, therefore, it can pass through holes of the sieve, thereby getting separated. Later, pulses are put in water, due to which lighter husk particles floats on top of water and pulses settles at the bottom. Thus, husk gets separated from pulses.

4. What is sieving? Where is it used?

Answer: Sieving is the process of separation of fine particles from bigger particles with the help of sieve. Mixture of fine particles and bigger particles is allowed to pass through holes, due to which, fine particles pass through the sieve and bigger particles remain in the sieve. In general, it is used to remove sand from grains and to remove husk from the flour.

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

Answer:

Mixture of sand and water can be separated by the process of sedimentation and decantation. Take the mixture of sand and water in a container and allow the mixture to stand still for sometime. As the sand is insoluble in water, it settles down at the bottom of the container. Tilt the container and pour clean water in another container. Thus, sand particles remains in the container and water gets separated.
Mixture of sand and water can also be separated by the process of filtration. Take a container and cover it using cloth or filter paper. Now, pour the mixture into this container. It can be observed that, sand particles remains on the cloth or filter paper, whereas, water passes into the container. Thus, sand and water gets separated.

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

Solution: Yes, sugar mixed with wheat flour can be separated. Sugar can be separated by a method called sieving. Take the mixture in the sieve and shake the sieve slowly. It can be observed that, sugar remains on the sieve and wheat flour is passed out through the holes of the sieve.

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

Answer: To obtain clear water from muddy water, there is need to separate mud from water. Take a container and cover its mouth using cloth or filter paper. Now, pour muddy water into this container. It can be observed that, mud remains on top of cloth or filter paper and clean water gets collected within the container.

8. Fill up the blanks

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

Answer: 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 ___________.

Answer: Filtration.

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

Answer: 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 ___________.

Answer: Sedimentation and decantation.

9. True or false?

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

Answer: False. [Mixture of milk and Water can not be separated.]

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

Answer: False. [Mixture of powdered salt and sugar can not be separated.]

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

Answer: False. [Sugar have a soluble property. So, while making tea sugar will dissolve in water and hence, cannot be separated.]

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

Answer: False.[Grain and husk can be separated with the process of handpicking.]

10. 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?

Answer: It is easy to dissolve sugar in warm water. Also, in warm water more sugar can be dissolved. Therefore, ice should be added after dissolving sugar, so that sugar can dissolve in water easily.

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