CIE Nov 2014 v1 Paper 3 Q1

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PMT You are to determine the enthalpy change of reaction, H, for the reaction shown below. Cu(s) + H2SO4(aq)CuSO4(aq) + H2(g) Since copper is an unreactive metal it does not react directly with dilute acids. You will therefore need tond the enthalpy change of reaction for two reactions that do occur. The equations for these two reactions are below. Mg(s) + H2SO4(aq)MgSO4(aq) + H2(g) Mg(s) + CuSO4(aq)MgSO4(aq) + Cu(s) Reaction 1 Reaction 2 You will carry out experiments tond the enthalpy changes for each of Reaction 1 and Reaction 2 and use these values to calculate the enthalpy change for the reaction of copper with sulfuric acid. TURN OVER FOR EXPERIMENTAL METHODUCLES 2014 9701/31/O/N/14 [Turn over<br /> PMT Determining the enthalpy change for Reaction 1 Mg(s) + H2SO4(aq)MgSO4(aq) + H2(g) Reaction 1 (a) Method FA 1 is 1.00 mol dm3 sulfuric acid, H2SO4. FA 2 is magnesium powder, Mg. Read through the method before you start any practical work and prepare a suitable table for your results.Weigh the stoppered tube containing FA 2. Record the mass. Support the plastic cup in the 250 cm3 beaker. Use the measuring cylinder to transfer 25 cm3 of FA 1 into the plastic cup. Measure the temperature of FA 1 in the plastic cup and start the stop clock. Record this temperature as being the temperature at time = 0. Measure, and record, the temperature of this FA 1 every half minute for 2 minutes. At time = 2 2 Measure the temperature of the mixture in the cup at time = 3 minutes and then every half minute up to time = 7 minutes. Continue stirring occasionally throughout this time. Weigh the stoppered tube that had contained FA 2. Record the mass. Calculate and record the mass of FA 2 added to the sulfuric acid. Rinse the plastic cup with water and shake to dry. 1 minutes add the FA 2 to the acid and stir carefully to reduce acid spray. II III IV VI [6]UCLES 2014 9701/31/O/N/14<br /> (b) (i) On the grid below plot a graph of temperature (y-axis) against time (x-axis). PMT (ii) Complete the graph by inserting two, straight lines of bestt:one to show the temperature up to time = 2 2 one to show the temperature after time = 2 2 1 minutes, 1 minutes. II III IVUCLES 2014 9701/31/O/N/14 [Turn over<br /> (iii) From your graph, use the two straight lines of bestt to calculate the change in temperature at time = 2 2 1 minutes. PMT temperature change =C [4] (c) Calculations (i) In the reaction in (a), the sulfuric acid was in excess. Without carrying out any additional tests, what observation could you have made during your experiment to con rm this?(ii) Calculate the energy change that occurred during the reaction in (a). [Assume that 4.2 J is needed to raise the temperature of 1.0 cm3 of solution by 1.0 C.] energy change =J (iii) Use your answer to (ii) to calculate the enthalpy change, in kJ mol1, for the reaction between sulfuric acid and magnesium. [Ar : Mg, 24.3] Mg(s) + H2SO4(aq)MgSO4(aq) + H2(g) Reaction 1 enthalpy change for Reaction 1 =kJ mol1 sign value [4]UCLES 2014 9701/31/O/N/14<br /> PMT Determining the enthalpy change for Reaction 2 Mg(s) + CuSO4(aq)MgSO4(aq) + Cu(s) Reaction 2 (d) Method FA 3 is 1.00 mol dm3 copper(II) sulfate, CuSO4. FA 4 and FA 5 are magnesium powder, Mg. Read through the method before you start any practical work and prepare a suitable table for your results.Weigh the stoppered tube containing FA 4. Record the mass. Support the plastic cup in the 250 cm3 beaker. Use the measuring cylinder to transfer 25 cm3 of FA 3 into the plastic cup. Measure the temperature of FA 3 in the plastic cup and record the temperature. Add the FA 4 to the FA 3 in the cup and stir the mixture constantly. Measure and record the maximum temperature reached during the reaction. Calculate and record the maximum temperature change that occurred during the reaction. Weigh the stoppered tube that had contained FA 4. Record the mass. Calculate and record the mass of FA 4 added to the copper(II) sulfate. Empty the contents of the plastic cup into the 100 cm3 beaker labelled waste. Rinse the plastic cup and shake to dry. Repeat this experiment using FA 5 in place of FA 4. [2]UCLES 2014 9701/31/O/N/14 [Turn over<br /> (e) Calculations (i) Using your results from (d), calculate the mean temperature rise. PMT (ii) Using your results from (d), calculate the mean mass of magnesium used. mean temperature rise =C (iii) Show, using a suitable calculation, that the copper(II) sulfate was in excess in these reactions. mean mass =g (iv) Using your values from (i) and (ii), calculate the enthalpy change, in kJ mol1, for the reaction between magnesium and copper(II) sulfate. [Assume that 4.2 J is needed to raise the temperature of 1.0 cm3 of solution by 1.0 C.] [Ar : Mg, 24.3] Mg(s) + CuSO4(aq)MgSO4(aq) + Cu(s) Reaction 2 enthalpy change for Reaction 2 =kJ mol1 sign value [4]UCLES 2014 9701/31/O/N/14<br /> PMT Enthalpy change for Reaction 3 Reaction 3 is shown below. Cu(s) + H2SO4(aq)CuSO4(aq) + H2(g) Reaction 3 (f) Use your values for the enthalpy changes for Reactions 1 and 2 to calculate the enthalpy change for Reaction 3. Mg(s) + H2SO4(aq)MgSO4(aq) + H2(g) Mg(s) + CuSO4(aq)MgSO4(aq) + Cu(s) Reaction 1 Reaction 2 Show clearly how you obtained your answer. (If you were unable to calculate the enthalpy changes for Reactions 1 and 2, you should assume that the value for Reaction 1 is444 kJ mol1 and that the value for Reaction 2 is504 kJ mol1. Note: these are not the correct values.) enthalpy change for Reaction 3 =kJ mol1 sign value [2] (g) (i) The method you used to determine the enthalpy change for Reaction 1 was more accurate than the method you used to determine the enthalpy change for Reaction 2. Suggest two reasons why the method used for Reaction 2 was less accurate. Explain your answers. 12(ii) A student suggested that the accuracy of the method used for Reaction 2 could be improved by using a larger volume of copper(II) sulfate. Is this a correct suggestion? Give a reason for your answer.[3]UCLES 2014 9701/31/O/N/14 [Total: 25] [Turn over<br />

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