Methods of separation

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All substances are not present in their pure form in nature. Most of the substances are present in the form of mixtures. We can separate useful components of the mixtures by using various methods of separation. You must have seen your mother separating stones or other impurities from rice by washing it before cooking it. You generally use different methods of separation in your daily life. 


Methods of Separating Mixtures 

You must have studied many separating techniques in chemistry of class VI, VII and IX. So, here in this article we are going to discuss various separation techniques so that if you have any doubts then you can clear through this article – 

  • Handpicking 

  • Threshing

  • Winnowing 

  • Sieving 

  • Sedimentation 

  • Decantation 

  • Filtration 

  • Evaporation 

  • Condensation 

  • Sublimation 

  • Distillation 

  • Fractional distillation 

  • Separating funnel 

  • Magnetic separation  

Now we will discuss all above stated types of separation methods in detail – 

Handpicking 

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If you want to separate black grapes from the mixture of black and green grapes, then you will simply pick black grapes using your hands from the mixture. So, the separation method in which components of a mixture can be separated by just picking them out by hands is called handpicking. 

Conditions for handpicking – Mixture should contain impurities of little larger size and different colors.

Threshing 

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This method of separation is generally used by farmers in agriculture during the harvesting of crops as it is used in separating edible part from non-edible part of grain. For example, the grain is separated from the stalks by beating it on the ground or large stone. 

Winnowing 

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It is an agricultural technique being used since ancient times. Now a days many machines are available for winnowing. Winnowing meaning is separation of grains from straw by the use of current of air. The word winnow is originated from old English word ‘windwian’ which means separation of mixture through wind. Winnowing can be defined as separation of heavier substance from lighter substance of a mixture using current of air or by blowing air. Corns are separated from straw by winnowing. 


Difference Between Winnowing and Threshing

If you also generally get confused between winnowing and threshing, then here we are providing you difference between winnowing and threshing to clear your doubt

S.No. 

Winnowing 

Threshing 

1. 

It is the process of separating husk from grains. 

It is the process of loosening the edible part (grain) from non-edible parts (chaff).

2. 

Farmers used to do it by making the grains and husk mixture to fall from the height. During this process husk gets separated by wind. 

Farmers used to do it by striking the crop on the hard surface. 

3. 

It is done after threshing. 

It is done before winnowing. 


Sieving 

You must have either used this separation technique or seen someone using this at home. Generally, mothers use this technique in kitchens to separate stones or other larger impurities from rava, rice etc. We use this technique in making tea also. 


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The separation technique in which we use porous sieve to remove the impurities of the mixture is called sieving. It only removes those impurities which are larger in size than the pores in the sieve. 

Sedimentation 

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Sedimentation is a separation technique in which heavier impurities present in water settle down at the bottom after some time if you keep the mixture still at one place. The heavier constituent which get settled at the bottom is known as sediment and the water above it is known as supernatant. 

Decantation 

Decantation is the technique of removal of water after using sedimentation technique. 


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Filtration 

Filtration is the method of separation in which impurities are removed from water by using a filter paper. 

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The solid impurity which we get on the filter paper is called residue and the water which passed through the filter paper and gets collected in conical flask is called filtrate. 

Evaporation 

It is used to separate those mixtures in which solvent is liquid and solute is soluble solid. As the name suggests, evaporation is the process of conversion of water into vapour. It is the method of separation in which liquid (solvent or organic solvent) evaporates and leaves the solid residue behind. For example, salt is obtained from sea water by evaporation. 

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Condensation 

Condensation is the process of conversion of vapours into liquid state. This process is used in many separation techniques to collect the vapours of pure substance. 


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Sublimation 

Sublimation is the process in which substance directly changes from solid state to liquid state. It is used as a separation technique for those mixtures which contain sublimable volatile substance and non-sublimable volatile components. Some substances such as ammonium chloride, camphor, naphthalene and anthracene are sublime substances. 

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Mixtures of ammonium chloride and salt can be separated by sublimation method of separation of mixtures. 

Distillation 

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It is used for the separation of components of a mixture containing two miscible liquids that boil without decomposition and have sufficient difference in their boiling point. In this technique liquid mixtures are boiled, vaporized, condensed and isolated. Mixture of acetone and water is separated by distillation. Boiling point of acetone is 56°∁ and water is 100°∁.

Fractional Distillation 

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It is same technique as distillation, but its apparatus has fractionating column also. So that it can separate mixture of miscible liquids which has difference in their boiling point less than 25K. Separation of different gases from air can be done by fractional distillation. 

Separating Funnel 

It is used to separate two immiscible liquids such as oil and water. This method is used in the extraction of iron also. The principle is that immiscible liquids separate out in layers depending on their densities. 

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Magnetic Separation 

It is used in the separation of components of those mixtures in which one component shows magnetic properties and another one doesn’t. It is used in the extraction of metals to separate the metal from its impurity. 


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