Methods for Separation of Mixture
General methods used for the separation of a mixture follows:
(i) Crystallisation This method is based on the differene in the solubility of the various compound dissolved a common solvent. e.g. a mixture of KNO3 and Nacl can be separated by this process.
(ii) By separatory funnel This method is used to separate a mixture of two immiscible liquids. e.g. mixture of oil
and water, extraction of iron from its ore.
(iii) Sublimation When a solid changes directly from solid to gaseous state on heating, the process is known as
sublimation. This process is used to separate such mixtures that contain a sublimable volatile component from a non-sublimable impurity. This process is generally used for the separation of naphthalene,anthracene, benzoic acid, camphor, NH4Cl, iodine etc.
Iodine (I2) is the only halogen which sublimes. NH4Cl sublimes due its decomposition.
(iv) Distillation This method is used for the purification of liquids which boils without decomposition and contain
non-volatile impurities. e.g. pure water can be obtained From sea water by distillation, mixture of ether and toluene, benzene and aniline, etc.
(v) Fractional distillation This process is used to separate a mixture of two or more miscible liquids which possess their boiling points within the limit of 10 to 15 K. e.g. petrol, diesel, kerosene.
(vi) Distillation under reduced pressure This process is used for those liquids which decomposes below their boiling point under reduced pressure, liquid boils at low temperature. Hence, the temperature for decomposition is not reached. Thus, this process is known as vacuum distillation, e.g. glycerol can be
separated by this method. lt is also used for the concentration of sugar cane juice in sugar industry.
(vii) Steam distillation It is used for the separation and purification of liquids which are appreciably volatile in steam from non-volatile components of mixture, e.g O-nitrophenol and p-nitrophenol are separated by this method. Aniline is also purified by this method.
(Viii) Evaporation It is the process by which soluble solids can be obtained from their solution by allowing the
solvent to vaporise, e.g. salt can be obtained from Sait solution by evaporation.
(ix) Chromatography It is a modern method proposed by Tswett in 1903. This method is based on the difference in the rates at which the components of a mixture are adsorbed on a suitable adsorbent.
This method has been used
(a) to separate o and p-nitrophenol,
(b) to separate blue and red dyes,
(c) to separate plant pigments and other natural products.
(x) Atmolysis It is used for separating the mixture of gases. This method is based on the difference in their rates of diffusion.
(xi) Dialysis The process of separating the colloidal particles
from those of crystalloids by ditfusion of mixture
through a parchment or animal membrane is known as
dialysis e.g. A ferric hydroxide sol can be purified by
this method.
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