TJC Prelim P4 Qn

1 9729/04/TJC Prelims/2017 [Turn over s CANDIDATE NAME CIVICS GROUP / CENTRE NO. / INDEX NO. / CHEMISTRY 9729/04 Paper 4 Practical 28 August 2017 2 hours 30 minutes Candidates answer on the Question Paper. READ THESE INSTRUCTIONS FIRST Write your Civics Group and name on all the work you hand in. Give details of the practical shift and laboratory where appropriate, in the boxes provided. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. The use of an approved scientific calculator is expected, where appropriate. You may lose marks if you do not show your working or if you do not use appropriate units. Qualitative Analysis Notes are printed on pages 14 and 15. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. Shift Laboratory This document consists of 15 printed pages. For Examiner’s Use 1 / 15 2 / 24 3 / 16 Total / 55 2017 JC2 PRELIMINARY EXAMINATIONS HIGHER 2

2 9729/04/TJC Prelims/2017 [Turn over Answer all the questions in the spaces provided. 1 Determination of change in oxidation number of a transition metal ion, M2+ You are to determine, by titration, the change in oxidation number of a transition metal ion, M2+, when reacted with acidified potassium manganate(VII). FA 1 FA 2 FA 3 is 0.0200 mol dm3 potassium manganate(VII), KMnO4 is 0.0470 mol dm3 transition metal salt, MSO4 is 1.00 mol dm3 sulfuric acid, H2SO4 (a) Method (i) 1. Fill the burette with FA 1. 2. Using a pipette, transfer 25.0 cm3 of FA 2 into the conical flask. 3. Using a measuring cylinder, transfer 25.0 cm3 of FA 3 to the same conical flask. 4. Carry out as many accurate titration s as necessary to obtain consistent results. Add FA 1 until the contents of the conical flask turns a permanent pale pink colour. 5. Record below, in a table form, all of your burette readings and the volume of FA 1 added in each accurate titration. Results [6] (ii) From your titrations, obtain a suitable volume of FA 1 to be used in your calculations. Show clearly how you obtained this volume. 25.0 cm3 of FA 2 required _______________ cm3 of FA 1 [1]

3 9729/04/TJC Prelims/2017 [Turn over (b) Calculations Show your working and appropriate significant figures in the final answer to each step of your calculations. (i) Calculate the amount of p otassium manganate(VII) present in the volume of FA 1 calculated in (a)(ii). amount of KMnO4 = [1] (ii) Determine the amount of MSO4 in 25.0 cm3 of FA 2. amount of MSO4 in 25.0 cm3 = [1] (iii) Use your answer to (b)(i) and (b)(ii) to calculate the number of moles of MSO4 that react with 1 mole of KMnO4 amount of MSO4 = [1] (iv) Two possible equations for the reaction of acidified KMnO4 with MSO4 are shown below: Equation 1: 2KMnO4 + 10MSO4 + 8H2SO4  K2SO4 + 2MnSO4 + 5M2(SO4)3 + 8H2O Equation 2: 2KMnO4 + 5MSO4 + 8H2SO4  K2SO4 + 2MnSO4 + 5M(SO4)2 + 8H2O State and explain which of the above two equations is consistent with your answer in (b)(iii). [1]

4 9729/04/TJC Prelims/2017 [Turn over (v) Use your answer in (b)(iv) to state the oxidation number of the transition metal M in the product of the reaction. [1] (c) (i) A student suggested that using a burette to measure 25.0 cm3 of FA 2 would give a more accurate result than using a pipette. The percentage error of a 25.0 cm3 pipette is 0.24%. Calculate the percentage error of using a burette and deduce if the above claim by the student is correct. [2] (ii) Another student decided to use a 25.0 cm3 pipette instead of a measuring cylinder to measure the volume of FA 3 in Step 3. State and explain whether this alteration will improve the accuracy of the experimental results. [1] [Total: 15]

5 9729/04/TJC Prelims/2017 [Turn over 2 Determination of the enthalpy change of neutralisation, ΔHn You are to determine the enthalpy change for the neutralisation reaction given below. HA(aq) + NaOH(aq) → NaA(aq) + H2O(l) FA 4 FA 5 is 1.80 mol dm–3 HA is aqueous sodium hydroxide, NaOH (a) Method Read through the instructions carefully and prepare a table below for your r esults before starting any practical work. 1. Support the styrofoam cup in the 250 cm3 beaker. 2. Rinse and fill the burette with FA 4. 3. Use the measuring cylinder to transfer 25 cm3 of FA 5 into the styrofoam cup. 4. Place the thermometer in the styrofoam cup and record the temperature of the solution. Tilt the cup if necessary to ensure the thermometer bulb is fully immersed. 5. Run 5.00 cm 3 of FA 4 into the cup. Stir, and record the new temperature of the solution and the volume of FA 4 added. 6. Run a second 5.00 cm3 of FA 4 into the cup. Stir and record the new temperature and the total volume of FA 4 added. 7. Continue adding FA 4 in 5.00 cm 3 portions. Stir and record each new temperature and total volume of FA 4 until a total of 45.00 cm3 has been added. Results [2]

6 9729/04/TJC Prelims/2017 [Turn over (b) (i) Plot a graph of temperature (y-axis) against total volume of FA 4 added (x-axis) on the grid below. The temperature axis should allow you to include a point at least 2 °C greater than the maximum temperature recorded. Draw two best-fit lines connecting all the plotted points with • an increasing trend • a decreasing trend. [3]

7 9729/04/TJC Prelims/2017 [Turn over (ii) Extrapolate the two lines until they cross. The intersection gives the maximum temperature, Tmax, at equivalence point. Use your graph to determine the following and show clearly on your graph how you obtained these answers.  Maximum temperature at the equivalence point, Tmax,  Maximum temperature change at the equivalence point, Tmax.  Total volume of FA 4 added at the equivalence point, Veq. Tmax = Tmax = Veq. = [3] (c) Explain the shapes of your graph lines before the equivalence point and after the equivalence point. (i) Before the equivalence point [2] (ii) After equivalence point [1]

8 9729/04/TJC Prelims/2017 [Turn over (d) Calculations Show your working and appropriate significant figures in the final answer to each step of your calculations. (i) Calculate the number of moles of HA present in the volume of FA 4 recorded in (b). Amount of HA = (ii) Using your answers in (b), calculate the heat energy produced when FA 4 neutralised 25 cm3 of sodium hydroxide. (Assume that 4.2 J of heat energy changes the temperature of 1.0 cm3 of solution by 1 °C.) Heat energy produced = (iii) Calculate the enthalpy change of neutralisation, in kJ mol–1, for the reaction below. HA(aq) + NaOH(aq) → NaA(aq) + H2O(l) Enthalpy change = [6] (e) Apart from using a thermometer calibrated to a greater level of precision, suggest one other improvement that could be made to the method carried out in (a). [1]

9 9729/04/TJC Prelims/2017 [Turn over Planning The enthalpy change of solution of solid NaOH ca