Assuming that copper contains only iron, silver and gold as impurities. After passage of 12.4 A for — Electrochemistry Chemistry Question
Question
Assuming that copper contains only iron, silver and gold as impurities. After passage of 12.4 A for 4825 s, the mass of anode decreased by 20.00 g and the cathode increased by 19.05 g. The percentages of iron and copper in the original sample are, respectively, (Cu = 63.5, Fe = 56)
💡 Solution & Explanation
Charge passed $Q = 12.4 \times 4825 = 59830$ C. Number of Faradays = $59830 / 96500 = 0.62$ F. The cathode gains only pure Cu. Moles of Cu deposited = $19.05 / 63.5 = 0.30$ mol, which corresponds to $0.30 \times 2 = 0.60$ F. At the anode, both Cu and Fe are oxidized (Ag and Au fall as anode mud). Let's test option (b): 95.25% Cu and 2.8% Fe. Mass of Cu in anode = $0.9525 \times 20.00 = 19.05$ g ($0.30$ mol, $0.60$ equivalents). Mass of Fe in anode = $0.028 \times 20.00 = 0.56$ g ($0.01$ mol, $0.02$ equivalents). Total equivalents of oxidation = $0.60 + 0.02 = 0.62$ F. This perfectly matches the total charge passed. Therefore, correct answer is B.