JPJC Prelim 2025 Paper 4 QP H2 Chem

© Jurong Pioneer Junior College [Turn Over NAME CLASS 24S JURONG PIONEER JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION 2025 CHEMISTRY 9729/04 Higher 2 Paper 4 Practical 26 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, class and exam index number 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 a 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 23 and 24. Shift At the end of the examination, fasten all your work securely together. Laboratory The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 11 2 19 3 13 4 12 Total 55 This document consists of 23 printed pages and 1 blank page.

2 © Jurong Pioneer Junior College 9729/04/J2 PRELIMINARY EXAM/2025 Answer all the questions in the spaces provided. 1 Determination of the enthalpy change for the reaction between NaOH and CO2 For Examiner’s Use In this experiment you will determine the enthalpy change, H1, for the reaction shown in equation 1. equation 1 NaOH(aq) + CO2(g) → NaHCO3(aq) H1 Sodium hydrogen carbonate and sodium hydroxide each react with sulfuric acid as shown in equations 2 and 3. equation 2 2NaHCO3(s) + H2SO4(aq) → Na2SO4(aq) + 2H2O(l) + 2CO2(g) H2 equation 3 2NaOH(aq) + H2SO4(aq) → Na2SO4(aq) + 2H2O(l) H3 You will determine the values of H2 and H3 and use Hess’s law to calculate H1. (a) (i) Reaction of sodium hydrogen carbonate with sulfuric acid FA 1 is solid sodium hydrogen carbonate FA 2 is 1.0 mol dm–3 sulfuric acid, H2SO4 In this experiment, you will measure the initial temperature of sulfuric acid in a polystyrene cup. After a sample of sodium hydrogen carbonate is added to sulfuric acid, which is in excess, you will measure the minimum temperature reached in the experiment . You will then determine the temperature fall caused by the reaction. In the space provided on page 3, prepare tables in which to record for the experiment: • all weighings to an appropriate level of precision, • all required temperature measurements to an appropriate level of precision. Procedure: 1. Weigh the capped bottle containing solid FA 1. 2. Using a measuring cylinder, transfer 50.0 cm 3 of FA 2 into a polystyrene cup. Place this cup inside a second polystyrene cup, which is placed in a 250 cm3 glass beaker. 3. Place the thermometer in this FA 2 and record the initial temperature, Ti. 4. Adding small quantities at a time, tip all the FA 1 into the FA 2 in the polystyrene cup. 5. Using the thermometer, stir the mixture continuously until it reaches its minimum temperature. Record this temperature, Tmin. 6. Calculate and record the temperature fall. 7. Weigh the capped bottle with any residual FA 1 and record the mass of FA 1 added.

3 © Jurong Pioneer Junior College 9729/04/J2 PRELIMINARY EXAM/2025 [Turn Over Results For Examiner’s Use [3] (a) (ii) Calculate the heat change, q, for your experiment in 1(a)(i). You should assume that the specific heat capacity of the solution is 4.18 J g−1 K−1, and that the density of the solution is 1.00 g cm−3. q = ……………………………… [1] (iii) Determine the enthalpy change for the reaction of sodium hydrogen carbonate with sulfuric acid, H2. In this reaction, sulfuric acid is used in excess. 2NaHCO3(s) + H2SO4(aq) → Na2SO4(aq) + 2H2O(l) + 2CO2(g) H2 Include the sign of H2 in your answer. [Ar: C, 12.0; H, 1.0; Na, 23.0; O, 16.0] H2 = ……………………………… [2]

4 © Jurong Pioneer Junior College 9729/04/J2 PRELIMINARY EXAM/2025 (b) Reaction of sodium hydroxide with sulfuric acid For Examiner’s Use FA 2 is 1.0 mol dm–3 sulfuric acid, H2SO4 A student conducted this experiment to determine the enthalpy change for the reaction of sodium hydroxide with sulfuric acid, H3. The student added 40.0 cm3 of FA 2 into 30.0 cm3 of 2.00 mol dm−3 NaOH in a polystyrene cup and recorded a temperature rise of 11.0 C. (i) Calculate the heat change, q, for the student’s experiment. You should assume that the specific heat capacity of the solution is 4.18 J g−1 K−1, and that the density of the solution is 1.00 g cm−3. q = ……………………………… [1] (ii) Determine the enthalpy change for the reaction of sodium hydroxide with sulfuric acid, H3. In this reaction, sulfuric acid is used in excess. 2NaOH(aq) + H2SO4(aq) → Na2SO4(aq) + 2H2O(l) H3 Include the sign of H3 in your answer. H3 = ……………………………… [2]

5 © Jurong Pioneer Junior College 9729/04/J2 PRELIMINARY EXAM/2025 [Turn Over (c) The enthalpy change of solution of NaHCO3 is +18.8 kJ mol−1. NaHCO3(s) + aq → NaHCO3(aq) Hsol = +18.8 kJ mol−1 2NaHCO3(s) + H2SO4(aq) → Na2SO4(aq) + 2H2O(l) + 2CO2(g) H2 2NaOH(aq) + H2SO4(aq) → Na2SO4(aq) + 2H2O(l) H3 For Examiner’s Use Using your answer in 1(a)(iii), 1(b)(ii) and Hsol given in this question, use Hess’s law to calculate H1. NaOH(aq) + CO2(g) → NaHCO3(aq) H1 H1 = ……………………………… [1] (d) Calculate the percentage error in the temperature fall you obtained in 1(a)(i). percentage error = ……………………………… [1] [Total: 11]

6 © Jurong Pioneer Junior College 9729/04/J2 PRELIMINARY EXAM/2025 2 Investigation of the kinetics of the autocatalytic reaction between manganate(V II) ions and ethanedioate ions. For Examiner’s Use FA 3 is 0.0100 mol dm–3 sodium thiosulfate, Na2S2O3 FA 4 is 0.0200 mol dm–3 potassium manganate(VII), KMnO4 FA 5 is 0.200 mol dm–3 ethanedioic acid, H2C2O4 FA 6 is 0.100 mol dm–3 potassium iodide, KI You are also provided with: • FA 2, 1.0 mol dm–3 sulfuric acid, H2SO4, which you used in Question 1 • Starch Indicator Manganate(VII) ions, MnO4–, react with ethanedioate ions, C 2O42−, in acidic medium as shown in equation 4. The Mn2+ ions produced in equation 4 act as a catalyst for the reaction. This is an example of an autocatalytic reaction. equation 4 2MnO4–(aq) + 5C2O42−(aq) + 16H+(aq) → 2Mn2+(aq) + 10CO2(g) + 8H2O(l) You will prepare a reaction mixture containing FA 4, FA 5 and FA 2. At timed intervals, you will transfer aliquots (portions) of the reaction mixture to excess K I solution which will “quench” the reaction by reacting away manganate(VII) ions as shown in equation 5. equation 5 2MnO4–(aq) + 10I−(aq) + 16H+(aq) → 2Mn2+(aq) + 5I2(aq) + 8H2O(l) You will then titrate the iodine produced in the resulting solution against sodium thiosulfate solution. The reaction is shown in equation 6. equation 6 2S2O32−(aq) + I2(aq) → 2I−(aq) + S4O62−(aq) Your titre values will indicate the concentration of MnO 4− remaining in the reaction mixture at different times. Hence, the r