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Methods of Separation - I

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Methods of Separation - I - Lesson Summary

In our day to day life we might have separate the useful substance from the mixture.  
For example rice and pulses are cleaned before they cooked. We find tiny stones, small insects and husk among the grains. We need to separate them before they are cooked.

Substances are mostly available in mixture s. A few substances are available in pure form. Hence, we need to separate the useful substance from the mixture by using some methods.
Before studying the various separation methods we should know the need to separate the components of a mixture.

Need for separation of substances
Substances need to be separated from each other to remove impurities or to get two or more useful products.

Separation of substances can be carried out under two conditions
     •  Dry conditions
     •  Wet conditions

Separation of substances under dry conditions
There are various methods for separating substances, such as handpicking, threshing, winnowing and sieving.

It involves simply picking out substances by hand and separating them from others. The substances being separated may be impurities that have to be thrown away or it may be that both the substances being separated are useful – such as if you separate green grapes from black ones from a mixture of the two.

This is done after harvesting of crops. Once wheat is harvested, the stalks are dried. Then, each grain of wheat is separated from the stalks to which it is attached, so that it can be ground into flour.
This method of separating grains from stalks is called threshing. It is basically the beating of the dry stalks to shake off the dried grains
It can be done by hand, by cattle, or by using machines. Traditionally, threshing was done by hand, but cattle help to do this job quickly. Nowadays, threshing machines are also used to separate large quantities of grain at a time. One of these machines is a combine harvester

Once the wheat has been threshed, the grains should be cleared of the husk and chaff before grinding into wheat flour.
The process of separation of lighter and heavier particles from the mixture by wind or blowing air is called winnowing. The chaff is separated from the grains by winnowing. In this method the farmer gently drops the mixture to the ground from a height. The heavier grains are collected at a place, while the lighter chaff blows away.

Sieving is used to separate substances that are of different sizes. In this method a sieve is used. The smaller components of the mixture can pass through the pores of the sieve whereas bigger components of the mixture are retained by the sieve.
For example, Wheat flour has some fine powdered wheat as well as some bigger impurities. When this flour is put through a sieve, the fine powder falls through the small holes in the sieve, while the thicker impurities remain as they are too big for these holes. And hence, the substances are separated. 


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