What amount of electricity is required to deposit one mole of aluminium from a solution of AlCl3?

Analyze the question: We need the quantity of electricity (charge) needed to deposit 1 mole of aluminium from AlCl₃ solution.

Concept: The charge needed depends on the number of electrons gained per ion. One mole of electrons carries 1 Faraday (about 96,500 C). Faraday is a unit of charge (quantity of electricity), while the ampere is a unit of current, not an amount of electricity.

Solution:

1. In solution, AlCl₃ gives Al³⁺ ions.
2. At the cathode: Al³⁺ + 3e⁻ → Al
3. To deposit 1 mole of Al, 3 moles of electrons are needed.
4. Charge = 3 × 96,500 C = 289,500 C, which is 3 Faradays.

Check the options:

• A. One Faraday deposits only 1/3 mole of Al, so this is wrong.
• B and D. The ampere is a unit of current, not an amount of electricity, so both are wrong.
• C. Three Faradays matches our working.

Tip: The number of Faradays needed to deposit 1 mole of a metal equals the charge on its ion. For example, Na⁺ needs 1 F, Cu²⁺ needs 2 F, and Al³⁺ needs 3 F. Also remember that amperes measure current, while Faradays and coulombs measure charge.