NYJC Prelim H2 Chem 9729 P4

[Turn Over H NANYANG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME TUTOR’S NAME CLASS CHEMISTRY 9729/04 Paper 4 Practical August 2025 2 hours 30 minutes Candidates answer on the Question Paper. Additional Materials: As listed in the Confidential Instructions READ THESE INSTRUCTIONS FIRST Write your name and class 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, 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 19 and 20. 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 For Examiner’s Use 1 / 13 2 / 15 3 / 14 4 / 13 Total / 55 This document consists of 20 printed pages

2 H2 Chemistry 9729/04 NYJC J2/2025 PRELIM 1 Determination of concentration of ethanedioic acid FA 1 is 0.023 mol dm–3 potassium manganate(VII), KMnO4. FA 2 is aqueous ethanedioic acid, H2C2O4, made by dissolving the hydrated salt, H2C2O4∙2H2O. You are also provided with 1.0 mol dm–3 sulfuric acid, H2SO4. In this experiment you are to determine the concentration, in g dm–3, of hydrated ethanedioic acid, H2C2O4∙2H2O, in FA 2. (a) Manganate(VII) ions, MnO4–, and ethanedioate ions, C2O42‒, undergo redox reaction in an acidic solution. Fill in the stoichiometric values for the reaction equation below. MnO4– + H+ + C2O42– → Mn2+ + H2O + CO2 [1] (b) Dilution of FA 2 1. Using a burette, measure between 42.50 cm3 and 43.00 cm3 of FA 2 into a 250 cm3 volumetric flask. Record the data in the space provided below. 2. Make the solution up to the mark with deionised water and shake well to mix. 3. Label this solution FA 3. Results

3 H2 Chemistry 9729/04 NYJC J2/2025 PRELIM [Turn Over Titration of FA 3 against FA 1 4. Fill a second burette with FA 1. 5. Use a pipette to transfer 25.0 cm3 of FA 3 into a 250 cm3 conical flask. 6. Using a measuring cylinder, transfer 25.0 cm3 of 1.0 mol dm–3 sulfuric acid and 40.0 cm3 of deionised water into the same flask and place the flask on a tripod stand. 7. Put a thermometer into the conical flask and heat the solution using a Bunsen flame until the temperature of the solution is just above 65 ºC. 8. Carefully remove the thermometer and place the flask under the second burette containing FA 1. If the neck of the flask is too hot to hold safely, use a folded paper towel to hold the flask. 9. Run 1 cm3 of FA 1 and swirl the flask until the colour of the potassium manganate(VII) has disappeared then continue titrati ng with FA 1. The end-point is reached when a permanent pale pink colour is obtained. If a brown colour appears during the titration, reheat the flask to 65 ºC. The brown colour should disappear and the titration can be completed as above. If the brown colour does not disappear on reheating, discard the solution and start the titration again. 10. Record your titration results, to an appropriate level of precision, in the space provided below. 11. Repeat steps 4 to 10 until consistent results are obtained. Titration results [2]

4 H2 Chemistry 9729/04 NYJC J2/2025 PRELIM (c) From your titrations, obtain a suitable volume of FA 1 to be used in your calculations. Show clearly how you obtained this volume. volume of FA 1 = cm3 [3] (d) (i) Calculate the amount of MnO4– ions present in the volume of FA 1 calculated in (c). amount of MnO4– ions = mol [1] (ii) Calculate the amount of C2O42– ions that reacted with MnO4– ions from the burette. amount of C2O42– ions = mol [1] (iii) Determine the concentration, in mol dm–3, of C2O42– ions in FA 3. concentration of C2O42– ions in FA 3 = mol dm–3 [1]

5 H2 Chemistry 9729/04 NYJC J2/2025 PRELIM [Turn Over (iv) Calculate the concentration, in mol dm–3, of C2O42– ions in FA 2. concentration of C2O42– ions in FA 2 = mol dm–3 [1] (v) Hence calculate the concentration, in g dm–3, of H2C2O4∙2H2O in FA 2. [Ar: H, 1.0; C, 12.0; O, 16.0] concentration of H2C2O4∙2H2O in FA 2 = g dm–3 [1] (e) Explain, in molecular terms, why (i) the initial reaction in Step 9 is slow even though the conical flask was heated above 65 ºC before titration. [1] (ii) the rate of reaction increases as the reaction progresses. [1] [Total: 13]

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7 H2 Chemistry 9729/04 NYJC J2/2025 PRELIM [Turn Over 2 Determination of the enthalpy change of solution for potassium chloride Solid FA 4 is anhydrous potassium chloride. (a) In this experiment, you will measure the temperature of the contents of a polystyrene cup at timed intervals, both before and after solid FA 4 is added. You will analyse your results graphically in order to determine an accurate value for the temperature change of the mixture, caused by dissolving solid FA 4. You will use this value to calculate the heat change, q, for the experiment and hence determine a value for the enthalpy change of solution for solid FA 4, Hsol. In an appropriate format in the space provided on page 8, prepare tables in which to record results for your experiment in (a): • all weighings to an appropriate level of precision, • all values of temperature, T, to an appropriate level of precision, • all values of time, t, recorded to the nearest 0.5 min. It is important that you measure each temperature at the specified time. Procedure 1. Weigh the capped bottle containing solid FA 4. 2. Place a polystyrene cup in a 250 cm3 beaker to prevent them from tipping over. 3. Use a 50 cm3 measuring cylinder to transfer 50 cm3 of deionised water into the polystyrene cup. 4. Stir the water in the cup with the thermometer. Read and record its temperature, T (time, t = 0.0 min). 5. Continue to stir the water. Read and record T every minute. 6. At exactly three minutes, transfer all the solid FA 4 to the polystyrene cup. Stir the mixture but do not read T. 7. Continue to stir the mixture. Read and record T at t = 3.5 min. 8. Continue to stir the mixture. Read and record T at t = 4.0 min and every minute until t = 9.0 min. 9. Reweigh the empty bottle and its cap.

8 H2 Chemistry 9729/04 NYJC J2/2025 PRELIM Results [4] (b) Plot a graph of temperature, T, on the y‒axis, against time, t, on the x‒axis on the grid in Fig. 2.1 on page 9. Draw a best ‒fit straight line taking into account all of the points befor e t = 3.0min. Draw another best ‒fit straight line taking into account all of the points after the temperature of the mixture has started to rise steadily. Extrapolate (extend) both lines to t = 3.0 min.

9 H2 Chemistry 9729/04 NYJC J2/2025 PRELIM [Turn Over Fig. 2.1 [4] (c) From your graph, read the minimum temperature, Tmin, and the maximum temperature, Tmax, at t = 3.0 min. Rec