Answer:
(a) Crystallisation: It involves
the preparation of saturated solution of the impure organic compound in a suitable
solvent at a higher temperature, i.e., near its boiling point. The solution so
formed is filtered while it is hot to remove insoluble impurities. The clear
solution is cooled when the solid organic compound separates out in the form of
fine crystals. The solid is filtered and dried. If a compound is highly soluble
in one solvent and sparingly soluble in other solvent then crystallization can
be carried out in the mixture of these solvents.
Fractional
crystallisation is used for the separation of mixture of two compounds
which are soluble in the same solvent but their solubilities are different.
Note:
Coloured impurities present with the solid can be removed by adsorption on the
surface of activated charcoal.
(b)
Distillation: It is most important method for purifying the organic liquids
Distillation is a process which involves two steps:
(i) Vaporisation
(ii) Condensation
Several
methods of distillation such as simple distillation, fractional distillation,
vacuum distillation, steam distillation etc., simple distillation is used for those
liquids which boil without decomposition. Similarly, steam distillation is used
for the purification of the liquids which are steam volatile. The type of distillation
depends mainly on the nature of organic liquid and the nature of impurities
present in it.
(c)
Chromatography: It is most efficient technique given by Tswett, a botanist
in 1906.
Chromatography is
based on selective distribution of the various constituents of a mixture
between two phases, a stationary phase and a moving or mobile phase. Different
constituents migrate, at a different rates, through the stationary phase. On
the basis of nature of stationary phase, the chromatography techniques are divided
as follows :
(a) When stationary phase is solid, the chromatography is known
as adsorption or column chromatography. Depending upon the nature of
mobile phase, partition chromatography is further classified as follows:
(b) When stationary
phase is liquid, the chromatography is known as partition chromatography.
Depending upon the nature of mobile phase, partition chromatography is further
classified as follows:
The most
common ones are:
(i) Column
chromatography or adsorption chromatography,
(ii) Thin
layer chromatography (TLC),
(iii) Paper
chromatography,
(iv) Gas
chromatography,
(v) Ion-exchange
chromatography.
You need to login to perform this action.
You will be redirected in
3 sec