Methods of Separation I


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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
mixtures. 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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Activities & Simulations

Activity 1 
has created student friendly animation on “Methods Used for Separation of Substances”. This animation imprints the various separation methods in students mind. This activity also explain why separating mixing up material can be useful. It explain each technique with an appropriate example along with good animation. At the end of the activity students also get questions related to this activity.
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Activity 2 has created an interactive video on “Methods of Separating Mixtures”. Students learn different separation methods on their own by doing activities. This activity also has interactive session in which students have different separating mixtures and apparatus. Student has to drag the separation mixture to the apparatus which would use to separate it. At the end of the activity students also get questions related to this activity.
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1 . what is handpicking ? When is this method used?


Handpicking is a method to remove slightly larger impurities like pieces of dirt,stones and husk from wheat,rice and...

2 . what is the differece between sedimentation and decantation

Sedimentation is the process of settling down of heavy insoluble impurities. Decantation is pouring out of clear water.

3 . How is salt obtained from sea water?

The sea water is first collected and it is kept for evaporation.When the water is fully evaporated the salt remains.By this way salt is obta...

4 . Define saturated solution . How would you prepare a saturated solution of sugar in water


As the temperature of the solvent increases, solubility increases. Additionally, pressure and the nature of the solut...

5 . what is sieving? where is it used?


An instrument with a meshed or perforated bottom used for seperating impure substances from fine substances or for s...