a.
When Pt
electrodes are used :
At anode :H2O→2H⊕+
1
2
O2+2e-
[Since oxidation potential of H2O>
oxidation potential of SO
2-
4
ion]
At cathode :Cu2++2e-→Cu
( Since reduction potential of Cu>
reduction potential of H2O)
.
b.
When Cu
electrode are used :
At anode :Cu
dissolves into solution to form Cu2+
ions.
At cathode :Cu
is depostited as cathdoe.
Since both the reduction and oxidation potential of Cu2+
and Cu
is greater than that of H2O
.