Predict the products of electrolysis in each of the following:
(i) An aqueous solution of AgNO3 with silver electrodes.
(ii) An aqueous solution of AgNO3 with platinum electrodes.
(i) At cathode:
The following reduction reactions compete to take place at the cathode.
Ag+(aq) + e- → Ag(s) ; E° = 0.80 V
H+(aq) + e- → 1/2 H2(g) ; E° = 0.00 V
The reaction with a higher value of E° takes place at the cathode. Therefore, deposition of silver will take place at the cathode.
At anode:
The Ag anode is attacked by NO3- ions. Therefore, the silver electrode at the anode dissolves in the solution to form Ag+.
(ii) At cathode:
The following reduction reactions compete to take place at the cathode.
Ag+(aq) + e- → Ag(s) ; E° = 0.80 V
H+(aq) + e- → 1/2 H2(g) ; E° = 0.00 V
The reaction with a higher value of E° takes place at the cathode. Therefore, deposition of silver will take place at the cathode.
At anode:
Since Pt electrodes are inert, the anode is not attacked by NO3- ions. Therefore, OH- or NO3- ions can be oxidized at the anode. But OH- ions having a lower discharge potential and get preference and decompose to liberate O2.
OH- → OH + e-
4OH- → 2H2O + O2