Question

Explain the principle of electrolytic refining with an example.

Answer 1

The crude metal is refined by electrolysis. It is carried out in an electrolytic cell containing an aqueous solution of the salts of the metal of interest. The rods of impure metal are used as anode and thin strips of pure metal are used as cathode.

The metal of interest dissolves from the anode passes into the solution while the same amount of metal ions from the solution will be deposited at the cathode. During electrolysis, the less electropositive impurities in the anode, settle down at the bottom and are removed as anode mud. Let us understand this process by considering the electrolytic refining of silver as an example.

Cathode: Pure silver

Anode: Impure silver rods

Electrolyte: Acidified aqueous solution of silver nitrate. When a current is passed through the electrodes the following reactions will take place.

Reaction at anode:

\[\ce{Ag_{(s)} -> {Ag}^+_{ (aq)} + 1e^-}\]

Reaction at cathode:

\[\ce{Ag^+_{ (aq)} + 1e^- -> Ag_{(s)}}\]

During electrolysis, at the anode, the silver atoms lose electrons and enter the solution. The positively charged silver cations migrate towards the cathode and get discharged by gaining electrons and deposited on the cathode. Other metals such as copper, zinc, etc., can also be refined by this process in a similar manner.