8   4 This question is about hydrated magnesium sulfate, MgSO4·7H2O. *(a) Devise an experimental procedure to determine the enthalpy change of solution for hydrated magnesium sulfate. MgSO4·7H2O(s) + aq → MgSO4(aq) Details of the method of calculation are not required. 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Turn over 9   .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 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.................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 10   (b) The enthalpy changes of solution for anhydrous and hydrated magnesium sulfate were found by experiment to be MgSO4(s) + aq → MgSO4(aq) ΔrH = –63.2 kJ mol–1 MgSO4·7H2O(s) + aq → MgSO4(aq) ΔrH = +15.7 kJ mol–1 Calculate, using Hess’s law, the enthalpy change for the hydration of anhydrous magnesium sulfate. Include a sign and units in your answer. MgSO4(s) + 7H2O(l) → MgSO4·7H2O(s) (2) (c) Explain how the enthalpy change of hydration of magnesium ions in magnesium sulfate is different from the enthalpy change of hydration of calcium ions in calcium sulfate. 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(Total for Question 4 = 10 marks) Turn over 11   5 This question is about electrochemical cells. (a) A diagram is shown of the apparatus that is used to measure the emf of a cell with a zinc/zinc(II) electrode and an acidified manganese(II)/manganate(VII) electrode system. Complete the labels Y and Z by naming the substances needed. Temperature and concentrations are not required. (3) solution of zinc nitrate (aq) salt bridge voltmeter Y ............................................................................... Z ............................................................................... ............................................................................... ............................................................................... V Zn 12   (b) Excess zinc is added to an acidified solution of sodium dichromate(VI). Some electrode data are given in the table. Electrode system E d / V Cr2+(aq) + 2e–  Cr(s) –0.91 Cr3+(aq) + e–  Cr2+(aq) –0.41 ½Cr2O7 2–(aq) + 7H+(aq) + 3e–  Cr3+(aq) + 3½H2O(l) +1.33 Zn2+(aq) + 2e–  Zn(s) –0.76 Explain, using only the data in the table, the final oxidation state of chromium that is formed when zinc is added to acidified dichromate(VI) ions. Include E d cell values where appropriate. Equations are not required. 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Turn over 13   (c) A cell diagram is shown. Ni(s) ½ Ni2+(aq) ½½ [NO3 –(aq) + 2H+(aq)], [NO2(g) + H2O(l)] ½ Pt(s) E d cell = +1.06 V Deduce the reduction half‑equation. State symbols are not required. (1) (d) State the direction of the electron flow in the hydrogen‑oxygen fuel cell shown. Justify your answer by reference to the redox processes in the cell. acidic electrolyte membrane hydrogen water oxygen cell load negative electrode positive electrode (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (e) State one advantage of the hydrogen‑oxygen fuel cell over the use of petrol as fuel in a vehicle. (1) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (Total for Question 5 = 12 marks)