Question

Commercial aluminium production is done by the electrolysis of a bath containing${\text{Al}}_{\text{2}}{\text{O}}_{\text{3}}$dissolved in molten ${\text{Na}}_{\text{3}}{\text{AlF}}_{\text{6}}$salt. Why isn’t it done by electrolysis of an aqueous${\text{AlCl}}_{\text{3}}$solution?

Short answer

Aluminium cannot be formed from aqueous solutions because of overvoltage.

Step-by-step solution

Concept Introduction

The process of dissolving ionic compounds into their constituent components by delivering a direct electric current through the complex in a fluid form is known as electrolysis. At the cathode, cations are reduced, whereas anions are oxidised.

Electrolysis of Aluminium

Due to overvoltage, not all ions can be converted into their free element form via electrolysis, including these –

• Cations of metals from Group$\text{1A}$.
• Cations of metals from Group$\text{2A}$and Aluminium from group$3A$ .
• The fluoride ion cannot be oxidized, while the rest of the halides can be.

${\text{Al}}_{\text{2}}{\text{O}}_{\text{3}}$cannot be electrolyzed from aqueous${\text{AlCl}}_{\text{3}}$ because $\text{Al}$metal cannot be formed from aqueous solutions because of overvoltage.

Therefore, due to $\text{Al}$overvoltage, metal cannot be formed.