Q21.124 CP - Chemistry: Molecular Nature Of Matter And Change

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?

Step-by-Step Solution

Answer

Aluminium cannot be formed from aqueous solutions because of overvoltage.

Step 1: 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.

Step 2: 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.