The electrolysis of other molten substances

2 marks · Easy

Write the balanced ionic half-equation for oxygen formation at the anode during the electrolysis of molten aluminium oxide.

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2O^{2-} \to O_2 + 4e^-

Also accept: 2O^{2-}(l) \to O_2(g) + 4e^-

Common mistakes: 2O^{2-} \to O_2 + 2e^-

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Marking points

M1 · 1 mark · Recognises 2 O^{2-} ions are needed to form one O_2 molecule.

A1 · 1 mark · Correctly writes the balanced half-equation: 2O^{2-} \to O_2 + 4e^-.

Worked solution

Each O_2- ion loses 2 electrons, and it takes two of them to form O_2.