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

Explanation

(i) Electrolytic refining : In this method , the impure metal is made to act as anode . A strip od the same metal in pure form is used as Cathode. They are put in a suitable electrolyte both containing soluble salt of the same metal . The more basic metal remains in the solution and the less basic ones go to the anode mud . the reactions are ,
Anode : `MtoM^(n+)+"ne"^(-)`
Cathode : `M^(n+)+"ne"^(-)toM`
Copper and zinc are refined by this method.
(ii) Vapour phase refining : In this method , the metal is converted into its volatile compound and collected elsewhere . It is then decomposable , so that recovery is easy.