Many salts contain water of crystallisation which can be removed by heating to form the anhydrous salt. You will determine the enthalpy change of dehydration for hydrated magnesium sulfate. MgSO4•7H2O(s) → MgSO4(s) + H2O(l) You will determine this enthalpy change by measuring the changes in temperature when samples of hydrated magnesium sulfate and anhydrous magnesium sulfate are dissolved separately in excess water. FA 3 is hydrated magnesium sulfate, MgSO4•7H2O. FA 4 is anhydrous magnesium sulfate, MgSO4·

1. (a)**Method** Experiment 1 • Weigh the container with FA 3. Record the mass in the space below. • Support the cup in the 250 cm³ beaker. • Rinse the 25 cm³ measuring cylinder with distilled water. Use the measuring cylinder to transfer 25.0 cm³ of distilled water into the cup. • Place the thermometer in the water and tilt the cup, if necessary, so that the bulb of the thermometer is fully covered. Record the temperature. • Tip all of the FA 3 into the water in the cup. Stir the mixture thoroughly. • Record the highest or lowest temperature of the mixture. • Calculate the change in temperature. Record this change. • Weigh the container with any remaining FA 3. Record the mass. • Calculate the mass of FA 3 used. Record this mass. Experiment 2 • Repeat the method using FA 4 in place of FA 3. Use the second cup. **Results** [Empty table with rows I to V on page 8 of the question paper][5]
2. (b)(i)Calculate the heat energy transferred, in J, in each experiment. Assume that 4.18J of heat energy changes the temperature of 1.0cm³ of solution by 1.0°C. Experiment 1 with FA 3 heat energy = .............................................. J Experiment 2 with FA 4 heat energy = .............................................. J[1]
3. (b)(ii)Calculate the enthalpy change, ΔH, in kJ mol⁻¹, when 1.0mol of solid dissolves in water in each experiment. Experiment 1 with FA 3 ΔH₁ = ...................... kJ mol⁻¹ sign value Experiment 2 with FA 4 ΔH₂ = ...................... kJ mol⁻¹ sign value[3]
4. (b)(iii)Use your answers to (b)(ii) to calculate the enthalpy change when 1.0mol of hydrated magnesium sulfate is dehydrated to form 1.0mol of anhydrous magnesium sulfate. MgSO4•7H2O(s) → MgSO4(s) + 7H2O(l) Show clearly, by a Hess's energy cycle or any other suitable means, how you calculated your answer. If you were unable to complete the calculation in (b)(ii) then assume that the enthalpy change in Experiment 1, ΔH₁, is +8.7 kJ mol⁻¹ and that the enthalpy change in Experiment 2, ΔH₂, is −15.5 kJ mol⁻¹. These may not be the correct values. enthalpy change of dehydration of MgSO4•7H2O = .............................................. kJ mol⁻¹ sign value[2]