A student writes half equations for the reactions at the electrodes in four electrolysis experiments.
Which half equation is not balanced?
Cu2++2e−→Cu\mathrm{Cu^{2+} + 2e^{-} \rightarrow Cu}Cu2++2e−→Cu
2Br−→Br2+2e−\mathrm{2Br^{-} \rightarrow Br_{2} + 2e^{-}}2Br−→Br2+2e−
2H++2e−→H2\mathrm{2H^{+} + 2e^{-} \rightarrow H_{2}}2H++2e−→H2
4OH−→O2+2H2O+2e−\mathrm{4OH^{-} \rightarrow O_{2} + 2H_{2}O + 2e^{-}}4OH−→O2+2H2O+2e−
52 exam-style questions on OCR GCSE Chemistry 3.4 Electrolysis, covering 3.4.1 Products formed at the electrodes in electrolysis and 3.4.2 The technique of electrolysis. Each one has a worked solution and a mark scheme showing where the marks go.