Task

11.2 g of iron was dissolved in excess dilute sulfuric acid. A 5 % potassium permanganate solution was then added (in the presence of sulfuric acid) until it stopped being decolourised. Excess sodium hydroxide solution was then added; the precipitate was separated and heated to constant mass. 1) Write the reaction of iron with dilute sulfuric acid, calculate the gas volume (L, STP) and explain why an iron(II), not iron(III), salt forms. 2) Balance the reaction of iron(II) sulfate with potassium permanganate by electron balance and find the mass of 5 % KMnO₄ solution used. 3) Write the reaction of iron(III) sulfate with sodium hydroxide, calculate the mass of the precipitate and state its colour. 4) Write the equation for heating the precipitate and find the mass of the solid residue. For every part, show the method (reaction equations, formulas, reasoning) and all calculations step by step.