Question

Why electrolysis of an aqueous solution cannot be used to extract aluminium?

Answer 1

Aluminium cannot be produced by the electrolysis of an aluminium salt dissolved in water because of the high reactivity of aluminium with the protons of water and the subsequent formation of hydrogen. As in aqueous solution, protons (H+) are preferentially reduced before Al3+ ions, leading to hydrogen evolution, the reduction of Al3+ requires to perform the electrolysis in a molten aluminium salt in the absence of water.

Answer 2

Electrolysis of an aqueous solution cannot be used to extract aluminium because the reduction potential of aluminium is less than water

Explanation:

• The reduction potential of aluminium is lower than that of water it means that it has lesser tendency to get reduced in an electrolysis than water .
• Highly reactive metals like aluminium, with lower reduction potentials than hydrogen are not electrolysed by aqueous solutions of their salts because their ions cannot be reduced at cathode in presence of water molecules.
• The normal reduction potential of aluminum is −1. 66V, which is lower than the reduction potential of water.
• Aluminium when electrolysed in an aqueous solution is more likely to be oxidized.

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