Question

During electrolysis of molten lead bromide, graphite anode is preferred to other electrodes. Give reasons.

Answer 1

Electrolysis:

1. It is a process in which electric current is passed to the liquid or molten state of an element or a mixture of two elements to induced a chemical reaction.
2. Oxidation takes place at anode and reduction takes place at cathode.
3. Cathode is the negative terminal end where as anode is the positive terminal end of the cell.

During electrolysis of molten lead bromide,

At Anode: $2{\mathrm{Br}}^{-}\to {\mathrm{Br}}_2+2{\mathrm{e}}^{-}$

at Cathode: ${\mathrm{Pb}}^{2+}+2{\mathrm{e}}^{-}\to \mathrm{Pb}$

As a result of electrolysis of molten ${\mathrm{PbBr}}_2$, dark reddish brown, highly reactive Bromine vapors are formed at anode which will react with anode metal if it is other than graphite. ${\mathrm{Br}}_2$ vapors have no action over graphite.
Thus, graphite anode is preferred to other electrodes.