An aqueous sodium sulfate solution contains sodium ions, Na+\mathrm{Na^{+}}Na+, and hydrogen ions, H+\mathrm{H^{+}}H+. During electrolysis with inert electrodes, hydrogen gas forms at the cathode.
Which half equation represents the reaction at the cathode?
H2→2H++2e−\mathrm{H_{2} \rightarrow 2H^{+} + 2e^{-}}H2→2H++2e−
2H++e−→H2\mathrm{2H^{+} + e^{-} \rightarrow H_{2}}2H++e−→H2
2H++2e−→H2\mathrm{2H^{+} + 2e^{-} \rightarrow H_{2}}2H++2e−→H2
Na++e−→Na\mathrm{Na^{+} + e^{-} \rightarrow Na}Na++e−→Na
134 exam-style questions on OCR GCSE Chemistry 3.1 Introducing chemical reactions, covering 3.1.1 Writing formulae and balanced chemical equations, 3.1.2 Formulae of compounds from ions, and state symbols, 3.1.3 Conservation of mass and observed changes in mass, 3.1.4 Half equations and balanced ionic equations, 3.1.5 The mole and the Avogadro constant, and 3.1.6 Stoichiometry, limiting reactants and reacting masses. Each one has a worked solution and a mark scheme showing where the marks go.