Outline the principles of refining of metals by the following methods :
(a) Electrolytic refining
(b) Zone refining
( c) Vapour phase refining.

Explanation

(i) Zone refining : It is based upon the principle that the impurities are more soluble in the molten state that in the solid state of metal.
(ii) Electrolytic refining : In this method, impure metal in taken as anode, while cathode is made up of pure strip of same metal. Electrolyte is the solution of a soluble salt of the metal. When electric current is passed, metal ions from electrolyte are deposited at cathode, white equal ions of metal dissolves from anode. As a result, pure metal transfers from anode to cathode.
(iii) Vapour phase refining : In this method, curde metal is freed from impurities by first converting it inot a sutabe volatile compound by heating it with a specific reagent at a lower temperature and then decomposing the volatile compound at some higher temperature to give the pure metal.