Question

Why are products of electrolysis of $AgNO_3$ different with silver electrodes and platinum electrodes?

Hint:

Active electrodes (metals) dissolve at the anode instead of releasing gas. Inert electrodes (Pt, graphite) do not.

Answer 1

Step 1: Nature of the electrodes.
Platinum is an inert electrode (does not dissolve). Silver is an active electrode (dissolves as $Ag \rightarrow Ag^+ + e^-$ at the anode).
Step 2: With Pt electrodes.
Cathode: $Ag^+$ ions reduce, silver deposits. Anode (Pt, inert): water is oxidised, $O_2$ gas is released ($2H_2O \rightarrow O_2 + 4H^+ + 4e^-$). The $AgNO_3$ concentration in solution decreases.
Step 3: With Ag electrodes.
Cathode: $Ag^+$ ions reduce, silver deposits as before. Anode (Ag, active): silver metal oxidises preferentially ($Ag \rightarrow Ag^+ + e^-$), replenishing the $Ag^+$ ions consumed at cathode. Solution concentration stays constant.
Step 4: Summary of difference.
With Pt: Ag deposits + $O_2$ released; solution concentration falls. With Ag: Ag transfers from anode to cathode; solution concentration unchanged.