Q1. Electrolysis of a dilute aqueous NaCl solution was carried out by passing a 20 milliampere current. The time required to liberate 0.02 mol of hydrogen gas at the cathode is:
A \(9.65 \times 10^{4}\) s
B \(28.95 \times 10^{4}\) s
C \(19.3 \times 10^{4}\) s Correct
D \(38.6 \times 10^{4}\) s
Explanation
At the cathode, hydrogen is formed by \(2H^+ + 2e^- \to H_2\), so 1 mol of hydrogen needs 2 faradays of charge. For 0.02 mol hydrogen, the charge needed is \(0.04F = 0.04 \times 96500 = 3860\) coulombs. The current is 20 milliampere, or 0.020 ampere. Hence \(t = Q/I = 3860/0.020 = 193000\) seconds, which is \(19.3 \times 10^4\) seconds. The smaller value uses only one electron per hydrogen molecule, while the larger values overcount the charge.