In electrolysis of water with inert electrodes in basic solution, what are the products at the cathode and anode respectively?

• A. Cathode: O2; Anode: H2
• B. Cathode: H2O; Anode: O2
• C. Cathode: H2; Anode: H2
• D. Cathode: H2; Anode: O2

Answer: (D)

In alkaline electrolysis with inert electrodes, the cathode is where reduction happens and the anode is where oxidation occurs. The hydrogen gas comes from the reduction of water: 2 H2O + 2 e− → H2 + 2 OH−, so hydrogen appears at the cathode. The oxidation happens on hydroxide ions at the anode: 4 OH− → O2 + 2 H2O + 4 e−, so oxygen appears at the anode. The overall reaction is 2 H2O → 2 H2 + O2. Therefore, the products are hydrogen at the cathode and oxygen at the anode.