TMJC 2025 H2 Chem P2 QP

CANDIDATE NAME CIVICS GROUP H2 CHEMISTRY 9729/02 Paper 2 Structured Questions 18 September 2025 2 hours Candidates answer on the Question Paper. Additional materials: Data Booklet This document consists of 24 printed pages. READ THESE INSTRUCTIONS FIRST Write your name and civics group in the spaces at the top of this page. Write in dark blue or black pen. You may use an HB pencil for any diagrams and graphs. Do not use 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. A Data Booklet is provided. The number of marks is given in brackets [ ] at the end of each question or part question. TAMPINES MERIDIAN JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION For Examiner’s Use 1 / 7 2 / 16 3 / 11 4 / 12 5 / 16 6 / 13 Total / 75

2 Tampines Meridian Junior College 2025 JC2 Preliminary Examination H2 Chemistry [Turn Over 1(a) The graph in Fig. 1.1 shows the atomic radii of some Period 4 metals. Fig. 1.1 (i) With reference to Fig. 1.1, explain briefly why the atomic radius of Ca is smaller than K. [1] (ii) With reference to Fig . 1.1, describe and explain why the atomic radii from Cr to Ni are relatively constant. [2] 0 50 100 150 200 250 K Ca Sc Ti V Cr Mn Fe Co Ni atomic radii/ pm elements

3 Tampines Meridian Junior College 2025 JC2 Preliminary Examination H2 Chemistry [Turn Over (b) (i) Shibuichi is an alloy of copper and silver and is used in traditional Japanese sword fittings. A particular sample of Shibuichi produced the following peaks in its mass spectrum as shown in Fig. 1.2. Fig. 1.2 Calculate the average Ar of copper from these data. [1] (ii) With reference to Fig. 1.2, state the number of protons and neutrons present in the atom with nucleon number 109. Number of protons: ____________ Number of neutrons: ___________ [1] 61.7 26.3 6.2 5.8 0 10 20 30 40 50 60 70 63 65 107 109 % abundance nucleon number

4 Tampines Meridian Junior College 2025 JC2 Preliminary Examination H2 Chemistry [Turn Over (c) Table 1.2 shows the successive ionisation energies of element B. Table 1.2 1st 2nd 3rd 4th 5th 6th 7th 8th I.E. / kJ mol-1 900 1800 3250 4900 6050 12690 14200 16250 (i) State which group does element B belongs to. [1] (ii) Both element A and element B are consecutive elements in the Periodic Table and that element A is positioned to the left of element B. Explain why the 3rd ionisation energy of element B is lower than element A. [1] [Total: 7]

5 Tampines Meridian Junior College 2025 JC2 Preliminary Examination H2 Chemistry [Turn Over 2 Adipic acid, HOOC(CH 2)4COOH, is a flexible food additive used as a gelling aid, firming and buffering agent and can be found in many foods. It is a dibasic acid that ionises in 2 stages. (a) (i) Write an expression for the first acid dissociation constant of adipic acid, Ka1. [1] (ii) Suggest a reason why the value of Ka2 is lower than that of Ka1. [1] A mixture of adipic acid and its potassium salt can function as a buffer. (iii) With the aid of a chemical equation, briefly explain how this mixture can act as a buffer when a small amount of base is added. The effects of Ka2 can be ignored in any buffer action. [2] stage 1 stage 2

6 Tampines Meridian Junior College 2025 JC2 Preliminary Examination H2 Chemistry [Turn Over (iv) Determine the volume of 0.200 mol dm-3 KOH(aq) that needs to be added to 100 cm3 of 0.200 mol dm-3 adipic acid to form a buffer of pH 4.7. [2] 3-hexenedioic acid can be converted to adipic acid and 3-bromohexanedioic acid which serve as precursors or intermediates for organic synthesis. (b) (i) Propose a 2 -step reaction synthesis to convert 3 -hexenedioic acid to D. Show clearly all reagents and conditions and the structures of intermediates for each step. O OH O OH O O OH O 3-hexenedioic acid D [3]

7 Tampines Meridian Junior College 2025 JC2 Preliminary Examination H2 Chemistry [Turn Over (ii) Another possible product that could be produced from the synthesis method in (i) is shown below. Suggest why D is more likely to be formed than E. O O OH O E [1] (c) A sample of 3-bromohexanedioic acid was able to rotate plane polarised light. After reacting with hot NaOH(aq) followed by acidification , the product obtained was no longer able to rotate plane polarised light. The reaction between 3-bromohexanedioic acid and NaOH(aq) is shown in the equation below. (i) Describe the mechanism for the reaction between 3-bromohexanedioic acid and NaOH(aq). Include all relevant lone pairs, dipoles, curly arrows and charges. [3]

8 Tampines Meridian Junior College 2025 JC2 Preliminary Examination H2 Chemistry [Turn Over (ii) State the type of isomerism displayed by the products of the above reaction. [1] (iii) Draw the isomers produced in the above reaction. [2] [Total: 16]

9 Tampines Meridian Junior College 2025 JC2 Preliminary Examination H2 Chemistry [Turn Over 3(a) Chlorate(V), ClO3–, reacts with chloride ions according to the equation as shown below. 2ClO3–(aq) + 2Cl–(aq) + 4H+(aq) Cl2(g) + 2ClO2(aq) + 2H2O(l) An experiment was conducted using a mixture in which the concentrations of the reactants are as follows: 4.80 x 10–4 mol dm-3 of ClO3–, 0.1 mol dm-3 of Cl– and 0.4 mol dm-3 of H+. At five-minute intervals, small samples of the reaction mixture were withdrawn, quenched and placed into the UV–vis spectrometer to record its absorbance value. The absorbance value corresponds to the concentration of the product ClO2. The graph of absorbance against time is shown in Fig. 3.1. Fig. 3.1 (i) Beer-Lambert’s Law states that the absorbance values is directly proportional to the concentration of absorbing species, c, as shown below. A = εcl where ε is the molar extinction coefficient and l is the path length, which is usually 1.0 cm. This equation can be used to calculate the absorbance value when maximum amount of ClO2 was formed. Calculate the concentration of ClO2 in the reaction mixture. Show that the maximum absorbance value of the reaction is 0.600, given that ε of C lO2 is 1250 mol–1 dm3 cm–1. [2] ⎯⎯ → 0 0.1 0.2 0.3 0.4 0.5 0.6 0 5 10 15 20 25 30 absorbance time/ min

10 Tampines Meridian Junior College 2025 JC2 Preliminary Examination H2 Chemistry [Turn Over (ii) With reference to Fig. 3.1, show that the reaction is first order with respect to ClO3–. Draw clearly any construction lines on the graph. [2] (iii) Another experiment was carried out using 2.40 x 10–4 mol dm-3 of ClO3– while keeping concentration of Cl– and H+ the same. Deduce the half–life of ClO3– in this experiment. [1] (b) A series of experiments were carried out to investigate the order of reaction with respect to H+. The results are shown in Table 3.2. Table 3.2 (i) Using the information in Table 3.2, determine the order of reaction with respect to H+. [2] Experiment [ClO3–] / mol dm–3 [Cl–] / mol dm–3 [H+] / mol dm–3 Initial rate / mol dm–3 s–1 1 0.050 0.100 0.300 3.38 x 10–4 2 0.100 0.100 0.100 7.50 x 10–5