Question

How is impure copper purified by electrolysis? Explain.

Answer 1

Impure copper is purified by the process of electrolysis. In this process, the electrolytic cell consists of a thick lump of impure copper as the anode and very thin piece of pure copper as the cathode. Acidified copper sulphate solution is used as the electrolyte.
When current is passed through the electrolyte, copper ions are generated at anode, that go into the electrolyte (copper sulphate solution). Then, these copper ions generated from the electrolyte are deposited at cathode. Next, impure anode becomes thin, while the cathode becomes thicker by the deposition of reddish brown pure copper metal. The copper deposited would be 99.9% pure. After electrolysis, these pure copper strips are separated and are then transformed into the required shapes.

In the electrolytic refining of copper, some of the impurities dissolve in the electrolyte, while metals like silver and gold, which are not soluble in acid, settle down under the anode. This is called anode mud. This anode mud is later recovered and the precious metals are separated.

Reaction at cathode: ${\mathrm{Cu}}^{2+}+2{\mathrm{e}}^{-}\stackrel{}{\to \mathrm{Cu}}$
Reaction at anode: $\mathrm{Cu}\stackrel{}{\to }{\mathrm{Cu}}^{2+}+2{\mathrm{e}}^{-}$