13.2 g of iron(III) alum were dissolved in water and reduced to an iron(II) ion solution by zinc and dilute sulfuric acid. The mixture was filtered and the filtrate and washings were made up to 500 cm3 in a standard volumetric flask. If 20.0 cm3 of this solution
required 26.5 cm3 of 0.0100 mol dm–3 KMnO4 for oxidation:
(a) give the ionic equation for the reduction of iron(III) ions by zinc metal. (b) Calculate the percentage by mass of iron in iron alum.