[Short Notes – E&B] NCERT Class VI – Science, Separation of Substances – Chapter 5
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we need to separate harmful or non-useful substances that may be mixed with it. Sometimes, we separate even useful components if we need to use them separately.
The substances to be separated may be particles of different sizes or materials. These may be solids, liquids or even gases.
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Methods of Separation
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Hand Picking
This method of handpicking can be used for separating slightly larger sized impurities like the pieces of dirt, stone, and husk from wheat, rice or pulses. The quantity of such impurities is usually not very large.
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Threshing
The process that is used to separate grain from stalks etc. is threshing. In this process, the stalks are beaten to free the grain seeds. Sometimes threshing is done with the help of bullocks. Machines are also used to thresh large quantities of grain.
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Winnowing
Winnowing is used to separate 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.
The husk particles are carried away by the wind. The seeds of grain get separated and form a heap near the platform for winnowing. The separated husk is used for many purposes such as fodder for cattle.
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Sieving
Sieving allows the fine flour particles to pass through the holes of the sieve while the bigger impurities remain on the sieve.
In a flour mill, impurities like husk and stones are removed from wheat before grinding it. Usually, a bagful of wheat is poured on a slanting sieve. The sieving removes pieces of stones, stalk and husk that may still remain with wheat after threshing and winnowing.
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Similar sieves being used at construction sites to separate pebbles and stones from
Sand.
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Sedimentation, Decantation and Filtration
Rice or pulses are usually washed before cooking. When water is added to these, the impurities like dust and soil, particles get separated. These impurities go into water, which becomes a little muddy.
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When the heavier component in a mixture settles after water is added to it, the process is called sedimentation. When the water (along with the dust) is removed, the process is called decantation.
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Filtration is the process of separating suspended solid matter from a liquid, by causing the latter to pass through the pores of some substance, called a filter.
To filter muddy water, a filter with very small spores is required. It can’t be filtered with a strainer or cloth. A filter paper is one such filter that has very fine pores in it.
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Fruit and vegetable juices are usually filtered before drinking to separate the seeds and solid particles of pulp. The method of filtration is also used in the process of preparing cottage cheese (paneer) in our homes.
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The process of conversion of water into its vapour is called evaporation. The process of evaporation takes place continuously wherever water is present.
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Process of making Salt ( by Evaporation)
Sea water contains many salts mixed in it. One of these salts is the common salt. When sea water is allowed to stand in shallow pits, water gets heated by sunlight and slowly turns into water vapour, through evaporation. In a few days, the water evaporates completely leaving behind the solid salts
Common salt is then obtained from this mixture of salts by further purification.
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Use of more than one method of separation
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Often, one method is not sufficient to separate the different substances present in a mixture. In such a situation, we need to use more than one of these methods.
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Condensation
The process of conversion of water vapour into its liquid form is called condensation.
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After adding a few spoons of salt, if you find that some salt remains undissolved and settles at the bottom of the beaker? If yes, this means that no more salt can be dissolved in the amount of water we have taken. The solution is now said to be saturated.
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Water dissolves different substances in different amounts.
More of a substance can be dissolved in a solution by heating it.
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