A 3.7 amp current is passed through an electrolytic cell, and Al3+ is reduced to Al at the cathode. What mass of solid aluminum is produced after six hours?

• A. 1.24 g
• B. 0.828 g
• C. 7.45 g
• D. 22.3 g

Answer: (C)

The key idea is how much aluminum mass you gain per unit of electric charge passed, using Faraday’s law of electrolysis. To deposit aluminum from Al3+, three electrons are needed for each aluminum atom, so the number of moles of Al produced is moles = Q / (nF), with n = 3 and F ≈ 96485 C/mol e−.

First find the total charge: Q = I × t. With a current of 3.7 A for six hours, t = 6 × 3600 = 21600 s, so Q = 3.7 × 21600 = 79,920 C.

Then the moles of aluminum produced: moles Al = Q / (nF) = 79,920 / (3 × 96485) ≈ 0.2763 mol.

Finally, convert to mass using the molar mass of aluminum, M ≈ 26.98 g/mol: mass = moles × M ≈ 0.2763 × 26.98 ≈ 7.45 g.

So about 7.45 g of aluminum is produced.