Molten aluminium oxide contains aluminium ions, Al3+\mathrm{Al^{3+}}Al3+, and oxide ions, O2−\mathrm{O^{2-}}O2−. During electrolysis, aluminium atoms, Al\mathrm{Al}Al, and oxygen molecules, O2\mathrm{O_2}O2, form.
Give the half equations for the reactions at the cathode and the anode.
Explain why four aluminium atoms form for every three oxygen molecules.
112 exam-style questions on OCR GCSE Chemistry 3.3 Types of chemical reactions, covering 3.3.1 Oxidation and reduction in terms of oxygen, 3.3.2 Acids, alkalis and neutralisation, 3.3.3 The pH scale and measuring pH, 3.3.4 Oxidation and reduction in terms of electrons, 3.3.5 Dilute and concentrated, weak and strong acids, and 3.3.6 Hydrogen ion concentration and pH. Each one has a worked solution and a mark scheme showing where the marks go.