NCERT Solution for Science Class 6 Chapter 5 – Separation Of Substances

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

Answer:

Sometimes, different components of a mixture are not useful or may be even harmful. So, we need to separate different components of the mixture.

For example :

After preparing the tea, the tea leaves are not useful.

Small stones present in rice are harmful. So we need to sepaate them.

  1. What is winnowing ? Where is it used ?

Answer:

Winnowing is a process of separating heavier and lighter components of a mixture by wind or by blowing air.

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

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

Answer:

This can be done by handpicking. The method of handpicking is normally used for separating slightly larger size  impurities like pieces of dirt, husk from pulses, followed by sedimentation and decantation.

  1. What is sieving ? Where is it used ?

Answer:

Sieving allows fine particles to pass through the holes of the sieve, while the bigger impurities remain on the sieve.

In a flour mill, impurities are removed from flour by sieving.

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

Answer:

Firstly mixture is allowed to stand in a glass. Sand settles at the bottom (sedimentation). Clear water present at the upper layer is poured in another glass (decantation).

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

Answer:

Yes, it can be done as follows:

The mixture of sugar and wheat is poured in lot of water.

It is filtered.

On the filter paper, wheat is obtained.

It is dried to get wheat flour.

The filterate is a sugar – water mixture.

This mixture is evaporated to get sugar.

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

Answer:

Muddy water is allowed to stand.

Mud settles at the bottom (sedimentation).

Upper layer is clear water.

It is decanted.

This water is filtered again to remove traces of mud particles.

  1. Fill up the blanks

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

(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 _

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

(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:

(a) threshing

(b) filtration

(c) evaporation

(d) decantation

  1. True or False ?

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

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

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

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

Answer:

(a) False

(b) False

(c) False

(d) False

  1. 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:

We should add ice to the lemonade after dissolving sugar.

It will be possible to dissolve more sugar before adding ice.

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