‘Lawn sand’ is spread over the grass in gardens to reduce the growth of moss. Lawn sand is a mixture of sand and iron(II) sulfate crystals, FeSO₄.7H₂O. Lawn sand usually contains 6–10% FeSO₄.7H₂O by mass. To determine the exact percentage by mass of FeSO₄.7H₂O present in a sample of lawn sand, a student devises the following experiment. step 1 Use a known mass of lawn sand to prepare 250.0 cm³ of solution A containing Fe²⁺(aq) ions. Solution A must have dilute sulfuric acid, H₂SO₄(aq), added to it before it is made up to 250 cm³. step 2 To determine the concentration of Fe²⁺(aq) in solution A, titrate a 25.00 cm³ sample of solution A against 0.0200 mol dm⁻³ aqueous potassium manganate(VII), KMnO₄(aq). The reaction which takes place during the titration is shown. MnO₄⁻(aq) + 8H⁺(aq) + 5Fe²⁺(aq) → Mn²⁺(aq) + 4H₂O(l) + 5Fe³⁺(aq)