2 In this experiment you will determine the enthalpy change, ΔH, for the reaction between aqueous copper(II) sulfate and zinc. The zinc is in excess. The method used in this question is slightly different from that used in Question 1. Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s) FA 3 is zinc powder, Zn.

1. (a)Method • Weigh a clean, dry plastic cup and record the mass. • Add between 1.8g and 2.0 g of zinc powder, FA 3, and record the mass. • Place the plastic cup in the 250 cm³ beaker. • Pour 25 cm³ of FA 1 into the 25 cm³ measuring cylinder. • Place the thermometer in the solution in the measuring cylinder and record the initial temperature. • Pour the 25 cm³ of FA 1 into the plastic cup. • Stir the contents of the cup and record the highest temperature of the mixture. Tilt the cup if necessary to ensure the thermometer bulb is fully covered. • Calculate and record the mass of FA 3 used and the change in temperature. Keep the remainder of FA 3 for use in Question 3. Results [3]
2. (b)(i)Use your answer to 1(c)(ii) and the volume of FA 1 used in 2(a) to calculate the enthalpy change, in kJ mol⁻¹, when 1 mole of CuSO4 reacts with zinc. (Assume 4.2 J of heat energy changes the temperature of 1.0 cm³ of the mixture by 1.0 °C.) enthalpy change = .............................................. kJ mol⁻¹ (sign) (value)[2]
3. (b)(ii)The maximum error in a single thermometer reading is ±0.5°C. Calculate the maximum percentage error in the temperature change for the experiment in (a). maximum percentage error = .............................................. %[1]
4. (c)A student decided to repeat this experiment using the same concentration of copper(II) sulfate solution and the same batch of zinc powder. However, 50 cm³ of FA 1 and double the mass of FA 3 were used. What effect would doubling the quantities of FA 1 and FA 3 have on the temperature rise? The possible results are listed below. The temperature rise would be approximately half that for the first experiment. [ ] The temperature rise would be approximately the same as that for the first experiment. [ ] The temperature rise would be approximately double that for the first experiment. [ ] Tick the box you think correct and explain your answer.[1]
5. (d)Use the information given in Question 1 and Question 2 and your answers to 1(c)(iv) and 2(b)(i) to construct a Hess' cycle diagram for the reaction between magnesium and zinc sulfate to form magnesium sulfate and zinc. Calculate the enthalpy change for this reaction. (If you were unable to complete the calculations then assume the enthalpy change for 1(c)(iv) is -320 kJ mol⁻¹ and the enthalpy change for 2(b)(i) is –201 kJ mol⁻¹. These are not the correct values.) enthalpy change = .............................................. kJ mol⁻¹ (sign) (value)[2]