In an experiment, 5.6 g of iron filings were added to excess dilute tetraoxosulphate(VI) acid. The reaction proceeded according to the equation: Fe(s) + H2SO4(aq) → FeSO4(aq) + H2(g) [Fe = 56, S = 32, O = 16, H = 1, Molar volume at STP = 22.4 dm³, Avogadro's number = 6.02 × 10²³] (a) Explain what is meant by the term 'stoichiometry' of a reaction. (2 marks) (b) Calculate: (i) The number of moles of iron that reacted. (2 marks) (ii) The mass of iron(II) tetraoxosulphate(VI) (FeSO4) produced. (3 marks) (iii) The volume of hydrogen gas evolved at STP. (2 marks) (iv) The number of atoms of hydrogen present in the volume of gas calculated in (b)(iii). (3 marks) (c) If the experiment were repeated using only 4.9 g of dilute H2SO4 (assume pure) instead of excess acid, identify the limiting reagent and calculate the mass of FeSO4 that would be produced. (4 marks) (d) State the colour change observed when a few drops of acidified potassium tetraoxomanganate(VII) solution are added to the FeSO4 solution produced. Give a reason for your answer. (2 marks)