Describe the principle behind each of the following
processes:

i. Vapour phase refining of a metal.

ii. Electrolytic refining of a metal

iii. Recovery of silver after silver ore was leached with NaCN.

(i) Vapour Phase refining: The impure metal is first converted to its unstable volatile compound which is evaporated and then decomposed by heating at higher temperature to give pure metal, leaving behind the impurities.

(ii) Electrolytic refining of a metal: In this method impure metal is made anode and a thin sheet of pure metal is made cathode, and are put in a suitable electrolyte containing soluble salt of same metal. On passing current the more basic metal remains in the solution and the less basic one go to the anode and gets deposited as anode mud

(iii) Recovery of silver after silver ore was leached with NaCN:

More basic and cheaper zinc can displace silver from the complex and silver metal can be recovered. NaCN acts as a leaching agent or oxidizing agent, thus oxidize Ag to Ag⁺ which then combine with CN^- ions to form respective soluble complex.

2[Ag(CN)₂]^- (aq) + Zn (s) → [Zn(CN)₄]^2- (aq) + 2Ag (s)