Write the principles of the following methods:
(i) Vapour phase refining
(ii) Zone refining
(iii) Chromatography

Explanation

(i) Vapour phase refining: In this method, crude metal is freed from impurities by first converting it into a suitable volatile compound by heating it with a specific reagent at lower temperature and then decomposing the volatile compound at some higher temperature to given the pure metal.
(ii) Zone refining: It is based upon the principle that the impurities are more soluble in the molten state than in the solid state of the metal.
(iii) Chromatography: It is based upon the principle that the different components of a mixture are adsorbed to different extents on an dsorbent