What is electro-refining? Explain with one example.

In electrolytic the impure metal is made to act as anode. A strip of the same metal in pure form is used as cathode. They are put in soluble salt of the same metal. The more basic metal remains in solution and less basic go to the anode mud.

Anode : M → Mⁿ⁺ + ne^-

Cathode : Mⁿ⁺ + ne^- → M

For example copper is refine using this method. Anodes are of impure copper and pure copper strips are taken as cathode. The electrolyte is acidified solution of copper sulphate and the net result of electrolysis is the transfer of copper in the pure form from the anode to the cathode:

Anode: Cu → Cu²⁺ +2e^-

Cathode : Cu²⁺ + 2e^-→ Cu