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Molten aluminium oxide is electrolysed at 1000 deg C to obtain aluminium metal, the cathode reaction being Al³+ + 3e⁻ -> Al (1 Faraday = 96500 C). How much electric charge is needed to deposit 5.12 kg of aluminium?

1. 5.49 * 10⁷ C of electric charge
2. 5.49 * 10⁴ C of electric charge
3. 5.49 * 10¹ C of electric charge
4. 1.83 * 10⁷ C of electric charge

Correct answer: 5.49 * 10⁷ C of electric charge

Solution

Deposition of one mole of Al requires 3 moles of electrons (3 Faradays). Total charge scales with the mass of Al deposited.

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