During the industrial extraction of aluminium, purified aluminium oxide (Al2O3\text{Al}_2\text{O}_3Al2O3) is dissolved in molten cryolite and electrolysed.
What is the correct half-equation for the reaction occurring at the positive electrode (anode)?
2O2−−4e−→O22\text{O}^{2-} - 4\text{e}^- \rightarrow \text{O}_22O2−−4e−→O2
Al3++3e−→Al\text{Al}^{3+} + 3\text{e}^- \rightarrow \text{Al}Al3++3e−→Al
2O2−+4e−→O22\text{O}^{2-} + 4\text{e}^- \rightarrow \text{O}_22O2−+4e−→O2
O2−−2e−→O2\text{O}^{2-} - 2\text{e}^- \rightarrow \text{O}_2O2−−2e−→O2
34 exam-style questions on OCR GCSE Chemistry Electrolysis. Each one has a worked solution and a mark scheme showing where the marks go.