Half-equations and balancing redox equationsAQA A-Level Chemistry: Mind map

Exam questions on Half-equations and balancing redox equations

1. Bromine is extracted from seawater by bubbling chlorine gas through it. The overall reaction is Cl₂(g) + 2Br⁻(aq) → 2Cl⁻(aq) + Br₂(aq).
   Write the half-equation for the reduction of chlorine and explain why electrons do not appear in the overall equation.2 marks
2. In acidic solution, orange dichromate(VI) ions, Cr₂O₇²⁻, are reduced to green chromium(III) ions, Cr³⁺, and water is formed. A student reacts acidified dichromate(VI) ions with a solution of iron(II) ions, which are oxidised to iron(III) ions, Fe³⁺.
   The iron(II) half-equation is Fe²⁺ → Fe³⁺ + e⁻. Combine it with the dichromate(VI) half-equation to give the overall ionic equation.2 marks
3. Iron(II) ions in a solution are titrated against 0.0200 mol dm⁻³ acidified potassium manganate(VII). In acidic solution the MnO₄⁻ ion is reduced to Mn²⁺ and the Fe²⁺ ion is oxidised to Fe³⁺. A 25.0 cm³ sample of the iron(II) solution required 22.40 cm³ of the manganate(VII) solution for complete reaction.
   Write the half-equation for the reduction of the MnO₄⁻ ion in acid and the half-equation for the oxidation of Fe²⁺, and combine them to give the overall ionic equation.3 marks