JPJC 2026 H2 Chem Prelim Paper 4 suggested solutions

© Jurong Pioneer Junior College [Turn Over NAME CLASS JURONG PIONEER JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION 2026 CHEMISTRY 9476/04 Higher 2 Paper 4 Practical 25 August 2026 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 18, 19 and 20. 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 13 2 12 3 25 Total 50 This document consists of 18 printed pages and 2 blank pages.

2 © Jurong Pioneer Junior College 9476/04/J2 PRELIMINARY EXAM/2026 Answer all the questions in the spaces provided. 1 Inorganic and Organic Qualitative Analysis For Examiner’s Use (a) FA 1 and FA 2 are salts containing the same transition metal but in different oxidation states. You are provided with solutions of FA 1 and FA 2. You are also provided with Solution S , 1% starch solution (Keep for use in Question 2). You will perform tests to identify the transition metal contained in FA 1 and FA 2. (i) Perform the tests described in Table 1.1, and record your observations in the table. Unless otherwise stated, the volumes given below are approximate and should be estimated rather than measured. Test and identify any gases evolved. If there is no observable change, write no observable change. Table 1.1 tests observations 1 To 1 cm depth of FA 1 in a test-tube add 1 cm depth of dilute sulfuric acid, followed by 1 cm depth of aqueous potassium iodide. To the resulting mixture, add a few drops of Solution S. Purple solution turns brown/ black deposits in brown solution. (✓1) With starch, solution turns blue-black/ black/ purplish black. (✓2) 2 To 1 cm depth of FA 2 in a test-tube add aqueous sodium hydroxide dropwise, with shaking, until in excess. Leave the mixture on standing for 2 minutes. Off-white/ light brown/ brown/ cream ppt. (✓3) ppt. insoluble in excess NaOH. (✓4) ppt. turning darker brown/darkened/brown. (✓5) To the resultant mixture, add 1 cm depth of hydrogen peroxide. ppt. turns black/ dark brown. (✓6) Brisk effervescence/ gas bubbles noted. (✓7) O2 (✓8) gas relights a glowing splint. (✓9) [4] /brown 8-9(✓)[4]; 6-7(✓)[3]; 4-5(✓) [2]; 2-3(✓) [1]

3 © Jurong Pioneer Junior College 9476/04/J2 PRELIMINARY EXAM/2026 [Turn Over (ii) Explain the observations in Test 2 as fully as you can, with reference to the reactions occurring. Identify the transition metal ion present in FA 2. The transition metal ion present in FA2: Mn2+. [3] • Off-white/ light brown/brown/cream ppt Mn(OH)2 formed with NaOH • Oxidation causes darkening of ppt. (or formed Mn(OH)3) • H2O2 oxidises ppt./ Mn(OH)2/ Mn(OH3) to MnO2/ compound of higher oxidation state • H2O2 undergoes catalytic decomposition to give O2 gas. (iii) State, with supporting evidence, the nature of FA 1. Nature of FA 1: oxidising or oxidising agent Evidence: FA 1 oxidises I-/ KI to I2 in Test 1/with KI. [2]

4 © Jurong Pioneer Junior College 9476/04/J2 PRELIMINARY EXAM/2026 (b) Before starting this analysis, ensure your Bunsen burner is turned off. You are provided with an organic liquid sample FA 3. The molecular formula of FA 3 is C3H6O2. You will perform tests to deduce the structure of FA 3. For Examiner’s Use (i) Perform the tests described in Table 1.2, and record your observations in Table 1.2. Observations in Test 4 have been recorded. Do not perform this test. Unless otherwise stated, the volumes given below are approximate and should be estimated rather than measured. If there is no observable change, write no observable change. Table 1.2 tests observations 1 To a 1 cm depth of FA 3 in a test-tube, add 2 cm depth of dilute sulfuric acid. Then add 2–3 drops of aqueous potassium manganate(VII). Warm the mixture in the hot water bath for two minutes. Purple KMnO4 decolourises. 2 Add 1 cm depth of aqueous silver nitrate to a test-tube. Then slowly add 1 cm depth of aqueous sodium hydroxide. Brown ppt. Add aqueous ammonia slowly, with shaking, until the precipitate just dissolves. You may use a clean glass rod to stir the mixture and help dissolve the precipitate. Colourless solution Add 1 cm depth of FA 3 to this mixture and shake the tube. Warm the mixture in the hot water bath for two minutes. Silver mirror/grey ppt formed. Important: After about 3 minutes, pour the mixture down the sink and wash out the test-tube several times with tap water. 3 To a 1 cm depth of FA 3 in a test-tube, add 10 drops of aqueous sodium hydroxide. Now add iodine solution dropwise, until a permanent yellow/orange colour is obtained. Warm the mixture in the hot water bath for two minutes. The structure proposed must be structure 1 or 3) Upon warming, a pale yellow ppt formed. 4 To a 1 cm depth of FA 3 in a test-tube, cautiously add a small piece of sodium metal. Effervescence observed. H2 gas produced extinguishes a lighted splint with a “pop” sound. [3]

5 © Jurong Pioneer Junior College 9476/04/J2 PRELIMINARY EXAM/2026 [Turn Over (ii) The molecular formula of FA 3 is C3H6O2. Use the observations recorded in Table 1.2 to deduce a possible structure of FA 3. ecf correct structure based on student’s tests’ results Structure 1 Structure 2 Structure 3 [1] [Total: 13] H C C C H H H OH O H This structure gives • Positive Test 1 • Positive Test 2 • Positive Test 3 H C C CH3 H OH O H C C C H H OH H O H This structure gives • Positive Test 1 • Positive Test 2 • Negative Test 3 This structure gives • Positive Test 1 • Negative Test 2 • Positive Test 3

6 © Jurong Pioneer Junior College 9476/04/J2 PRELIMINARY EXAM/2026 2 Investigating the kinetics of the reaction between iodate( V) ions and hydrogensulfite ions For Examiner’s Use FA 4 is 0.100 mol dm–3 potassium iodate(V), KIO3. FA 5 is 0.0500 mol dm–3 sodium hydrogensulfite, NaHSO3. You are also provided with: • Solution S, 1% starch solution • deionised water • a waste beaker containing sodium carbonate solution Iodate(V) ions, IO3⁻(aq) react with hydrogensulfite ions, HSO 3⁻(aq) as shown in equation 1. equation 1 2IO3⁻(aq) + 5HSO3⁻(aq) → I2(aq) + 5SO42⁻(aq) + 3H+(aq) + H2O(l) In this experiment, the rate of the reaction is studied by measuring the rate of formation of iodine using a 'clock' method. You will vary the concentration of iodate( V) ions and measure the time taken for a fixed amount of iodine to be produced, which will be indicated by the formation of a blue-black colour in the presence of starch. The blue-black/ purple colour does not appear immediately because the iodine, I2(aq), produced can be reacted immediately with unreacted hydrogensulfite ions, HSO3⁻(aq), in a competing reaction (fast) as shown in equation 2.