Oxidation states and redoxAQA A-Level Chemistry: Mind map

Exam questions on Oxidation states and redox

1. In a titration, a solution of iron(II) ions is oxidised by acidified potassium manganate(VII). The manganate(VII) ion, MnO₄⁻, is reduced to Mn²⁺, and the iron(II) ions are oxidised to iron(III) ions, Fe³⁺.
   State the changes in oxidation state of manganese and of iron, and identify the reducing agent.2 marks
2. A technician is checking the oxidation states of an element in a range of compounds: sodium hydride, NaH; hydrogen peroxide, H₂O₂; potassium dichromate(VI), K₂Cr₂O₇; and sodium thiosulfate, Na₂S₂O₃.
   Deduce the oxidation state of chromium in K₂Cr₂O₇ and of sulfur in Na₂S₂O₃. Show your working.2 marks
3. Solid sodium iodide reacts with concentrated sulfuric acid. Iodide ions are oxidised to iodine, and sulfuric acid is reduced to hydrogen sulfide. The ionic equation is 8I⁻ + 10H⁺ + SO₄²⁻ → 4I₂ + H₂S + 4H₂O.
   Explain, in terms of electrons and oxidation states, why iodide ions are oxidised in this reaction and identify the oxidising agent.3 marks