Question

The reaction that takes place at the negative electrode (cathode) in the electrolysis of molten aluminium oxide is:
(Al^3+ + 3e^- Al)
(2O^2- O_2 + 4e^-)
(C + O_2 CO_2)
(Al_2O_3 2Al^3+ + 3O^2-)

• A. 1
• B. 2
• C. 3
• D. 4

Hint:

An easy way to remember: RED CAT (Reduction at Cathode) and AN OX (Anode Oxidation).

Answer 1

The Correct Option is A

The question pertains to the electrolysis of molten aluminium oxide (Al₂O₃), commonly known as the Hall-Héroult process, which is crucial in extracting aluminium from its ore. It asks us to identify the reaction that occurs at the negative electrode (cathode).

1. Understanding Electrolysis of Al₂O₃: In electrolysis, the cathode (negative electrode) is the site of reduction (gain of electrons). For aluminium extraction, aluminum ions (Al³⁺) are reduced to form aluminum metal.
2. Reaction at the Cathode: The specific reaction that occurs at the cathode during electrolysis of aluminum oxide is: 
   \(Al^{3+} + 3e^- \rightarrow Al\)
   This corresponds to Option 1.
3. Reaction Analysis:
   • Option 1 (\(Al^{3+} + 3e^- \rightarrow Al\)) is the correct answer as it represents the reduction of aluminum ions to aluminum.
   • Option 2 (\(2O^{2-} \rightarrow O_2 + 4e^-\)) takes place at the anode (positive electrode) where oxygen is released, not at the cathode.
   • Option 3 (\(C + O_2 \rightarrow CO_2\)) describes a reaction associated with carbon anodes but not directly part of the cathodic reaction.
   • Option 4 (\(Al_2O_3 \rightarrow 2Al^{3+} + 3O^{2-}\)) represents the dissociation of aluminum oxide into ions, but not a cathode reaction.

Thus, the correct reaction occurring at the cathode during the electrolysis of molten aluminum oxide is Option 1: \(Al^{3+} + 3e^- \rightarrow Al\).