MI Prelim H2 Chem P4 QP for exchange

Class Adm No Candidate Name: This question paper consists of 16 printed pages and 2 blank pages. 2025 Preliminary Examination Pre-University 3 H2 CHEMISTRY 9729/04 Paper 4 Practical 28 Aug 2025 2 hours 30 minutes Candidates answer on the Question paper. READ THESE INSTRUCTIONS FIRST Do not turn over this question paper until you are told to do so. Write your name, class and admission 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 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 16 and 17. 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. Question 1 2 3 4 Total Marks 8 28 11 8 55 H Shift Laboratory

2 1 Identification of anions FA 1 is an aqueous solution containing two anions. You will perform tests to identify the two anions in FA 1. You are not expected to identify the cations. Unless otherwise stated, the volumes given below are approximate and should be estimated rather than measured. Test and identify any gases evolved. (a) Carry out the following tests. Carefully record your observations in Table 1.1. Table 1.1 tests observations 1 Test FA 1 solution using Universal Indicator paper. 2 To a 1 cm depth of FA 1 in a clean test- tube, add 1 cm depth of aqueous silver nitrate. Add excess aqueous ammonia. 3 To a 1 cm depth of FA 1 in a clean boiling tube, add a small piece of aluminium foil into the boiling tube, then heat gently over a Bunsen flame. 4 To a 1 cm depth of FA 1 in a clean test- tube, add 2 cm depth of dilute hydrochloric acid. No effervescence observed [4]

3 [Turn over (b) Identify the two anions in FA 1 and state the evidence for each anion by completing Table 1.2. The evidence given must be sufficiently conclusive in identifying the anions. Table 1.2 anion evidence [4] [Total: 8]

4 2 Investigation on a solution of oxalic acid Oxalic acid is a common organic acid containing the carboxylic acid functional group. You will perform two separate experiments to investigate its properties. (a) Determination of concentration and enthalpy change of neutralisation by thermometric titration Oxalic acid is an organic acid that occurs naturally in many foods, such as quinoa and rhubarb leaves. It is known to be a dibasic acid, potentially donating two H+ ions per molecule of oxalic acid. FA 2 is aqueous oxalic acid of unknown concentration. FA 3 is 2.2 mol dm-3 sodium hydroxide, NaOH. Prepare a table in the space provided on page 6 and record, to the appropriate level of precision: • all volumes of FA 3 added, V • the maximum temperature, T, after each addition of FA 3 It is important that the volume of FA 3 recorded is the total volume you have added up to the point when the temperature reading was made. Procedure 1. Place a polystyrene cup inside a second polystyrene cup and place both cups in a glass beaker. 2. Use a pipette to transfer 10.0 cm3 of FA 2 into the polystyrene cup. 3. Fill the burette with FA 3. 4. Stir the FA 2 in the cup gently with the thermometer. Read and record its temperature, tilting the cup to ensure that the bulb of thermometer is fully submerged in the solution. 5. Use the burette to add 2.00 cm3 of FA 3 to the cup and stir the mixture gently with the thermometer. Read and record both the maximum temperature and the actual total volume of FA 3 added. 6. Repeat step 5 until a total of 30.00 cm3 of FA 3 has been added. For each addition of FA 3, read and record both the maximum temperature, T, and the actual total volume of FA 3 added up to that point, V. Note: If you overshoot on an addition, record the actual total volume of FA 3 added up to that point.

5 [Turn over BLANK PAGE

6 Results [3]

7 [Turn over (i) Plot a graph of temperature, T, on the y-axis, against total volume of FA 3, V, on the x-axis on the grid in Fig. 2.1. Your scale on the y-axis should allow for extrapolation above the highest temperature recorded. Draw two lines of best fit, taking into account the points when the temperature of the mixture was rising and the points when the temperature was falling. Each line should have a shape best suited to its plotted points. Extrapolate both lines until they intersect. Fig 2.1 [3]

8 (ii) Explain the shape of your line of best-fit drawn in (a)(i), when the temperature is falling. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… ………………………………………………………………………………………………… [2] (iii) Hence, f rom your graph, identify the total volume of FA 3 added at the point of neutralisation, Vneut. Vneut = …………………….…………… Using the initial temperature of FA 2, Tinitial, and the maximum temperature of the mixture from the graph, Tmax, calculate the change in temperature, ΔT. Tinitial = …………………….…………… Tmax = …………………….…………… ΔT = …………………….…………… [4] (iv) Determine the concentration of oxalic acid in FA 2. concentration of oxalic acid in FA 2 = ……………………………... [2]

9 [Turn over (v) Calculate the heat change, q, at the point of neutralisation in your 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 1.0 g cm−3. q = ……………………………... [1] (vi) Calculate the enthalpy change of neutralisation, ΔHneut, for the reaction between oxalic acid and sodium hydroxide. ΔHneut = ……………………………... [3] (vii) The enthalpy change of neutralisation for hydrochloric acid reacting with sodium hydroxide is −57.3 kJ mol−1. Comment on your value of ΔHneut obtained in (a)(vi). …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… ………………………………………………………………………………………………… [2]

10 (b) Determination of concentration by acid-base titration The concentration of oxalic acid can also be determined via a simple acid-base titration. Procedure 1. Fill the burette with FA 3. 2. Use a pipette to transfer 10.0 cm3 of FA 2 into a 250 cm3 conical flask. 3. Add 2-3 drops of thymol blue indicator. 4. Titrate FA 2 against FA 3. The end-point is reached when the mixture first turns blue. 5. Record your titration results, to an appropriate level of precision, in the space provided below. 6. Repeat steps 2 to 5 until consistent results are obtained. Results [4] (i) From your titrations, obtain a suitable volume of FA 3 to be used in your calculations. Show clearly how you obtained this volume. volume of FA 3 = ……………………………... cm3 [1]