A 10 g sample of impure iron(II) sulphate, FeSO₄, was dissolved in water to make 250 cm³ of solution. Exactly 25.0 cm³ of the solution was titrated with 0.025 mol/dm³ potassium manganate(VII) until the solution just turned pink. The volume of potassium manganate(VII) that reacted was 23.5 cm³. MnO₄⁻ + 8H⁺ + 5Fe²⁺ → Mn²⁺ + 5Fe³⁺ + 4H₂O

1. aCalculate the number of moles in 23.5 cm³ of 0.025 mol/dm³ potassium manganate(VII). [2]
2. bCalculate the number of moles of iron(II) sulphate in 25.0 cm³ of solution. [2]
3. cCalculate the number of moles of iron(II) sulphate in 250 cm³ of solution. [2]
4. dCalculate the mass of iron(II) sulphate in the sample (Mr FeSO₄ = 152). [2]
5. eCalculate the percentage of purity of the sample. [2]
6. fWhat type of reaction occurred when Fe²⁺ changed to Fe³⁺? Explain your answer. [2]

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