NYJC Prelim H2 Chem 9729 P2

[Turn Over NANYANG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS TUTOR’S NAME CHEMISTRY 9729/02 Paper 2 Structured Questions September 2025 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. 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. If additional space is required, you should use the pages at the end of this booklet. The question number must be clearly shown. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. 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. For Examiner’s Use 1 / 9 2 / 12 3 / 8 4 / 21 5 / 25 Total / 75 This document consists of 19 printed pages. H

2 H2 Chemistry 9729/02 NYJC J2/2025 Prelim Answer all the questions in the spaces provided. 1 (a) Fig. 1.1 below can be used to plot the first ionisation energy of the elements from proton number 12 to 20. Six of these elements have been plotted already. Fig. 1.1 (i) Estimate and plot, on Fig. 1.1 above, the first ionisation energies of elements with proton numbers 13, 16 and 20. [1] (ii) Explain the general increase in first ionisation energy across elements with proton numbers 12 to 18. …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... ………………………………………………………………………………………………...[2] (iii) Write the electronic configurations of the elements with proton numbers 15 and 16, and hence, explain the trend in their first ionisation energies. …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... ………………………………………………………………………………………………...[2]

3 H2 Chemistry 9729/02 NYJC J2/2025 Prelim [Turn Over (b) Electric cables used in fire alarm systems have copper wire surrounded by magnesium oxide, which acts as insulator. (i) In terms of structure and bonding, explain why copper can conduct electricity. Draw a labelled diagram to illustrate your answer. …………………………………………………………………………………………………... …………………………………………………………………………………………………... ………………………………………………………………………………………………...[2] (ii) Suggest, in terms of structure and bonding, why magnesium oxide is a better insulator than sodium oxide. …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... ………………………………………………………………………………………………...[2] [Total: 9]

4 H2 Chemistry 9729/02 NYJC J2/2025 Prelim 2 (a) 2-bromobutane, CH3CHBrCH2CH3, undergoes nucleophilic substitution with aqueous sodium hydroxide to form butan-2-ol, CH3CH(OH)CH2CH3. CH3CHBrCH2CH3 + NaOH → CH3CH(OH)CH2CH3 + NaBr Two experiments were performed to determine the order of reaction with respect to the reactants. Fig. 2.1 shows the graph of [NaOH] against time when different initial concentrations of 2-bromobutane were used. The initial concentration of NaOH was kept at 0.010 mol dm−3. Fig. 2.1 (i) Explain what is meant by the term order of reaction with respect to the reactant. …………………………………………………………………………………………………... ………………………………………………………………………………………………..[1] (ii) Use the graph in Fig. 2.1 to prove that the order of reaction with respect to NaOH is zero and that of CH3CHBrCH2CH3 is one. …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... ………………………………………………………………………………………………..[2] 0 0.002 0.004 0.006 0 5 10 15 20 25 0.008 0.010 time / minutes [NaOH] / mol dm−3 [CH3CHBrCH2CH3] = 0.50 mol dm−3 [CH3CHBrCH2CH3] = 0.25 mol dm−3

5 H2 Chemistry 9729/02 NYJC J2/2025 Prelim [Turn Over (iii) Calculate the value of rate constant of the reaction. Include its units. [1] (iv) With reference to the order of reactions in (ii), suggest a mechanism for the nucleophilic substitution of 2-bromobutane. Show all relevant lone pairs, dipoles, curly arrows and charges. [2] (v) Explain why the butan-2-ol formed via the mechanism in (iv) does not rotate the plane polarised light. …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... ………………………………………………………………………………………………...[2]

6 H2 Chemistry 9729/02 NYJC J2/2025 Prelim (b) 2-bromobutane, CH3CHBrCH2CH3 exhibits stereoisomerism. It also reacts with NaOH in ethanol to form two constitutional isomers W and X. (i) Describe what is meant by stereoisomerism. …………………………………………………………………………………………………... ………………………………………………………………………………………………...[1] (ii) Draw the pair of stereoisomers for 2-bromobutane, CH3CHBrCH2CH3. [1] (iii) Draw the structures of W and X. [1] (iv) State which product W or X makes up a larger proportion of the reaction mixture. Explain your answer. …………………………………………………………………………………………………... …………………………………………………………………………………………………... ………………………………………………………………………………………………...[1] [Total: 12] W X

7 H2 Chemistry 9729/02 NYJC J2/2025 Prelim [Turn Over 3 A student wants to plate a leaf with a thin layer of cobalt. He first coated the leaf with graphite. The leaf and a platinum electrode were then immersed into an aqueous solution of cobalt(II) sulfate and electroplating was carried out. (a) Draw a fully labelled diagram of the set-up. [1] (b) State the equations, with state symbols, for the processes occurring at the anode and cathode. cathode: ………………………………………………………………………………………………… anode: ………………………………………………………………………………………………...[2] (c) After some time, the leaf was coated with a 0.20 mm layer of cobalt. Given that the surface area of the leaf was 10 cm2 and the density of cobalt metal is 8.90 g cm–3, calculate the volume of gas produced at the platinum electrode at room temperature. [2] (d) Calculate the time taken, in hours, to coat the leaf in (c) if the current used was 0.5 A. [1]

8 H2 Chemistry 9729/02 NYJC J2/2025 Prelim (e) Use data in the Data Booklet to explain any observations at each electrode over a long period of time when the platinum electrode is replaced with a dull grey solid lead.