Question detail
Why are carbon anodes gradually used up during the electrolysis of aluminium oxide in the Hall–Héroult process?
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
Question
Type
exam_style
Style
Topic
Electrolysis
Question
Why are carbon anodes gradually used up during the electrolysis of aluminium oxide in the Hall–Héroult process?
Answer
Because the oxide ions (O²⁻) in the molten aluminium oxide are oxidised at the carbon anode to form carbon dioxide, consuming the carbon electrode. The reaction is 2O²⁻ → O₂ + 4e⁻ and 4C + O₂ → 4CO₂, so the carbon anode is progressively consumed.
Explanation
The question tests understanding of the anode reaction in aluminium extraction, linking the reactivity of oxide ions with the consumption of the carbon electrode.
Common mistake
Misunderstanding Anode Consumption
Students often think that carbon anodes are used up because they react with the aluminium being extracted, rather than understanding that they are consumed by reacting with oxygen produced during the electrolysis process.
Emphasize that carbon anodes are gradually used up due to the reaction with oxygen, forming carbon dioxide, rather than being consumed by the aluminium itself.
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