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Oxidation–Reduction · Part 2 of 3
9 exam-style questions with model answers, plus 12 quick multi-choice questions — every question on this part of the standard, grouped by the 3 pages of notes they come from.
Write a full answer before you reveal the model one. That comparison is where the learning happens.
Write balanced half equations for (a) aluminium metal being oxidised to Al3+, and (b) bromine being reduced to bromide ions.
A student writes the half equation Cl2(aq) + e− → Cl−(aq) for the reduction of chlorine. Explain the two errors and give the correct half equation.
Explain why a half equation must have electrons on one side only, and justify the claim that checking the charge is a more reliable test of a half equation than checking the atoms.
Balance the half equation for the reduction of hydrogen peroxide to water in acidic solution, showing your steps.
Balance the half equation for the reduction of the iodate ion, IO3−, to iodine, I2, in acidic solution, and explain how the electron count can be confirmed from the oxidation numbers.
Explain why acidified potassium permanganate is used rather than a neutral solution, and evaluate what would be observed if a student forgot to add the acid.
Combine the half equations Al(s) → Al3+(aq) + 3e− and Cu2+(aq) + 2e− → Cu(s) into a balanced overall equation.
Acidified permanganate reacts with hydrogen peroxide. Write the overall equation, and explain how the observations follow from it.
A student combines the permanganate and iron(II) half equations and obtains MnO4− + 8H+ + Fe2+ → Mn2+ + 4H2O + Fe3+ + 4e−. Analyse the error, give the correct equation, and justify why the presence of electrons in a final equation is always fatal to the answer.