2025 DHS H2 Chem Prelim Paper 2 QP

© DHS 2025 9729/02 [Turn over Name: Centre/Index Number: Class: DUNMAN HIGH SCHOOL Preliminary Examination Year 6 H2 CHEMISTRY Paper 2 Structured Questions Candidates answer on the Question Paper. Additional Materials: Data Booklet 9729/02 18 September 2025 2 hours READ THESE INSTRUCTIONS FIRST Write your centre number, index number, name and class at the top of this page. 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. A Data Booklet is provided. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 15 2 17 3 12 4 10 5 21 Total 75 This document consists of 20 printed pages and 4 blank pages.

2 © DHS 2025 9729/02 Answer all the questions in the spaces provided. 1 (a) Fig. 1. 1 shows the relative first ionisation energies of six consecutive elements, A to F, in the Periodic Table with atomic number less than 20. The letters are not the symbols of the elements. Fig. 1.1 (i) Write an equation to represent the first ionisation energy of A. ……………………………………………………………………………………… [1] (ii) Explain why the first ionisation energy of F is more than that of E. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. ……………………………………………………………………………………… [1] (iii) Which element has the highest 4th ionisation energy? Explain your answer. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. ……………………………………………………………………………………… [1] (iv) Element E is in Period 3. Identify element E and state the number of electron pairs in an atom of E. …………………………………………………………………………………………. ……………………………………………………………………………………… [1]

3 © DHS 2025 9729/02 [Turn over (b) 10.0 cm 3 of 0.10 mol dm −3 aqueous bromine was added to 50.00 cm 3 of a 0.10 mol dm−3 sodium hydroxide solution. The products formed were Br− and BrOx−. The excess sodium hydroxide required 15.00 cm3 of 0.20 mol dm−3 hydrochloric acid for complete neutralisation. Calculate the mole ratio between aqueous bromine and sodium hydroxide in the redox reaction. Hence write a balanced equation for the reaction and deduce the value of x. [3]

4 © DHS 2025 9729/02 (c) The halogens Cl2 and I2 both react similarly with H2S. The reaction of Cl2 with H2S is shown in equation 1. equation 1 Cl2 + H2S → 2HCl + S (i) Predict which halogen, Cl2 or I2, has a greater reactivity when added to H2S. Explain your answer in terms of the role of the halogen in these reactions. …………………………………………………………………………………………. ……………………………………………………………………………………… [1] (ii) The white fuming gaseous products, HC l and HI, were collected in separate jars. A piece of red-hot wire was plunged into each jar and purple fumes were observed in one of them. Explain the observation. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. ……………………………………………………………………………………… [2] (iii) Both HI(g) and HCl(g) dissolve readily in water. Suggest a reagent, other than aqueous silver nitrate, that could be used to distinguish between the aqueous solutions of these two gases. Describe the expected observations. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. ……………………………………………………………………………………… [2]

5 © DHS 2025 9729/02 [Turn over (d) Bromine and fluorine react together to give bromine trifluoride. Br2(l) + 3F2(g) → 2BrF3(l) Using the data in Table 1.1, together with data from the Data Booklet, construct a fully labelled energy cycle to calculate the average bond energy of the Br−F bond in BrF3. Table 1.1 H / kJ mol−1 standard enthalpy change of formation of BrF3(l) −301 enthalpy change of vaporisation of Br2(l) +31 enthalpy change of vaporisation of BrF3(l) +44 [3] [Total: 15]

6 © DHS 2025 9729/02 2 The kinetics of the Finkelstein reaction between bromobutane and sodium iodide in propanone forming solid sodium bromide was studied in a series of experiments. Br + NaI I + NaBr(s) (a) In experiment 1, 10.0 cm 3 of 0.10 mol dm –3 bromobutane and 15.0 cm 3 of 1.0 mol dm–3 sodium iodide were mixed. Fig. 2.1 shows the concentration of bromobutane against time, t, for this experiment. Fig. 2.1 (i) Use the graph in Fig. 2.1 to determine the order of reaction with respect to bromobutane. Show your working clearly. …………………………………………………………………………………………. ……………………………………………………………………………………… [2] (ii) By drawing a tangent at t = 0 s, determine the initial rate of reaction. Include its units. [2] 0.000 0.005 0.010 0.015 0.020 0.025 0.030 0.035 0.040 0.045 0 100 200 300 400 500 600 700 800 900 1000 time, t / s [bromobutane] / mol dm−3

7 © DHS 2025 9729/02 [Turn over (b) In experiments 2 and 3, the time taken for a small and fixed amount of NaBr(s) to be formed was measured. The results obtained are found in Table 2.1. Table 2.1 experiment initial [bromobutane] / mol dm–3 initial [sodium iodide] / mol dm–3 time / s 2 0.60 0.60 21 3 0.40 0.40 47 (i) Use Table 2.1 to determine the order of reaction with respect to sodium iodide. Show your working clearly. [1] (ii) Use your answers to (a)(i) and (b)(i) to write the rate equation for the reaction between bromobutane and sodium iodide. State the units of the rate constant, k. …………………………………………………………………………………………. ……………………………………………………………………………………… [1] (iii) Hence use the initial rate of reaction from (a)(ii) to calculate the value of the rate constant, k. [2]

8 © DHS 2025 9729/02 (c) The Finkelstein reaction is a nucleophilic substitution reaction that can occur via the SN1 or SN2 mechanism. (i) Using your answer to (b)(ii), identify the mechanism for the reaction between bromobutane and sodium iodide. Suggest a reason why this is the predominant mechanism. …………………………………………………………………………………………. …………………………………………………………………………………………. ……………………………………………………………………………………… [1] (ii) Hence draw the mechanism for the reaction between bromobutane and sodium iodide. Use curly arrows to show the movement of electrons, and include relevant dipoles and lone pair of electrons. [2]

9 © DHS 2025 9729/02 [Turn over (d) The graph of pV/RT against p for one mole of iodobutane gas at 200 °C is shown in Fig. 2.2. Fig. 2.2 (i) State two basic assumptions of the kinetic theory as applied to an ideal gas. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. ……………………………………………………………………………………… [2] The boiling points of bromobutane and iodobutane are given in Table 2.2. Table 2.2 boiling point / °C bromobutane 101 iodobutane 131 (ii) Hence show in Fig. 2.2 how one mole of bromobutane will behave at the same te