How many faradays are required to produce one mole of water in a hydrogen-oxygen fuel cell containing an aqueous alkali as the electrolyte?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 2
One faraday (1 F) is the charge on one mole of electrons. In the hydrogen-oxygen fuel cell with aqueous alkali, oxygen is reduced at the cathode and hydrogen is oxidised at the anode:
Cathode: \( \displaystyle \ce{O2(g) + 2H2O(l) + 4e^- -> 4OH^-(aq)} \)
Anode: \( \displaystyle \ce{2H2(g) + 4OH^-(aq) -> 4H2O(l) + 4e^-} \)
Net reaction: \( \displaystyle \ce{2H2(g) + O2(g) -> 2H2O(l)} \)
Electrons per 2 mol of water: 4 mol of electrons pass through the circuit.
Electrons per 1 mol of water: \( \frac{4}{2} \) = 2 mol of electrons.
Charge: 2 mol of electrons = 2 F.