2025 Prelim P2 QP (for exchange) H2 Chem HCI

This document consists of 20 printed pages and 2 blank pages. HWA CHONG INSTITUTION C2 Preliminary Examination Higher 2 CANDIDATE NAME CT GROUP 2 4 S CENTRE NUMBER S INDEX NUMBER CHEMISTRY Paper 2 Structured Questions 9729/02 3 September 2025 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, CT group, centre number and index number on all the work you hand in. Write in dark blue or black pen. You may use a HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. DO NOT WRITE ON ANY BARCODES. Answer all questions in the spaces provided in the Question Paper. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. For Examiner’s Use 1 / 10 2 / 18 3 / 14 4 / 14 5 / 19 Deductions (s.f.) Deductions (units) Deductions (structures) Total / 75

2 © Hwa Chong Institution 2025 9729/02/C2 Preliminary Examination DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN [Turn Over Answer all questions in the space provided. 1 (a) In Fig.1.1, sketch a graph to show the variation of ionic radius across Period 3. Explain the shape of your graph. Na Mg Al Si P S Cl Fig.1.1 ……………………………………………………….…………………………………………..….……… ……………………………………………………….…………………………………………..….……… ……………………………………………………….………………………………………..…….……… ……………………………………………………….………………………………………...…….…….. ……………………………………………………….………………………………………..…….……… ……………………………………………………….………………………………………..…….……… ……………………………………………………….………………………………………...…….…….. ……………………………………………………….………………………………………..…….……… ……………………………………………………….……………………………………….……….… [3] (b) Write an equation for the reaction of P4O10 with water. State the pH of the resulting mixture. equation …...……………………..……………………….……………………………………….……… pH ..………………………………..……...………….…………………………………….……...…… [1] (c) Describe the acid-base behaviour of A l2O3 by reference to its reaction separately with sulfuric acid, H2SO4, and with sodium hydroxide, NaOH. Write equations for any reactions described. ……………………………………………………….………………………………………..…….……… ……………………………………………………….………………………………………...…….…….. ……………………………………………………….………………………………………..…….……… ……………………………………………………….……………………………………….……….… [2] ionic radius

3 © Hwa Chong Institution 2025 9729/02/C2 Preliminary Examination DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN [Turn Over (d) Aluminium chloride, AlCl3, and beryllium chloride, BeCl2, can act as Lewis acids. (i) Explain what is meant by a Lewis acid. ……………………………………………………….……………………………………….……… ……………………………………...………….…………………………………….……...…… [1] (ii) When heated with A lCl3, b romine monochloride, BrC l, reacts with benzene in an electrophilic substitution reaction to produce bromobenzene. Describe the mechanism for this reaction. In your answer, s how how the electrophile is generated and include relevant lone pairs of electrons, dipoles and curly arrows. [2] (iii) In the solid form, BeCl2 molecules polymerise to make long chains by forming co-ordinate (dative covalent) bonds. Draw a diagram to represent part of a beryllium chloride polymer which contains at least three repeat units of BeCl2. Label the co-ordinate bonds on your diagram. The bonding in the beryllium chloride polymer is similar to that in Al2Cl6(g). [1] [Total: 10]

4 © Hwa Chong Institution 2025 9729/02/C2 Preliminary Examination DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN [Turn Over 2 (a) In an experiment, 25.0 cm3 of 0.500 mol dm−3 LiOH(aq) was mixed rapidly in a polystyrene cup with 40.0 cm3 of 0.500 mol dm−3 HCl(aq), as shown in reaction 2.1. reaction 2.1 LiOH(aq) + HCl(aq) → LiCl(aq) + H2O(l) ∆H neut ꝋ The initial temperature of each solution is 27.8 °C and the final temperature of the mixture is 30.5 °C. (i) Define the term standard enthalpy change of neutralisation. ……………………………………………………….………………………………………..…..…. ……………………………………………………….……………………………………….……… ………………………………………………….…………………………………….……...…… [1] (ii) Calculate the standard enthalpy change of neutralisation of lithium h ydroxide, ∆H neut ꝋ , assuming that the solutions have a density of 1.00 g cm−3 and a specific heat capacity of 4.18 J g−1 °C−1. [2]

5 © Hwa Chong Institution 2025 9729/02/C2 Preliminary Examination DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN [Turn Over (b) Lithium hydroxide is used in air purification systems, particularly in enclosed environments like spacecrafts and submarines, to absorb carbon dioxide from the air. It achieves this by reacting with carbon dioxide to form lithium carbonate and water, as shown in reaction 2.2. reaction 2.2 2LiOH(s) + CO2(g) → Li2CO3(s) + H2O(l) ∆H 2 ꝋ (i) Construct an energy cycle to determine the standard enthalpy change of reaction 2.2, ∆H 2 ꝋ, using your answer in (a)(ii) and the data below. LiOH(s) → Li+(aq) + OH− (aq) ∆H 3 ꝋ = −21.0 kJ mol−1 Li₂CO₃(s) + 2HCl(aq) → 2LiCl(aq) + CO₂(g) + H₂O(l) ∆H 4 ꝋ = −29.0 kJ mol−1 If you were unable to calculate a value for the standard enthalpy change of neutralisation of lithium hydroxide in (a)(ii), you should use −48.2 kJ mol−1. This is not the correct answer. [3] (ii) Deduce the sign of the entropy change for reaction 2.2, ∆S 2 ꝋ, and hence predict the effect of increasing temperature on the spontaneity of reaction 2.2, using your answer in (b)(i). ……………………………………………………….…………………………………….……...….… ……………………………………………………….…………………………………….…………… ……………………………………………………….…………………………………….…………… ……………………………………………………….…………………………………….…..….….… ……………………………………………………….…………………………………….……...….… ……………………………………………………….…………………………………….………... [2]

6 © Hwa Chong Institution 2025 9729/02/C2 Preliminary Examination DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN [Turn Over (iii) A spacecraft mission to the moon is planned with 8 crewmembers and supplied with 250 canisters of LiOH to purify the air via reaction 2.2. Each canister carries 5.2 kg of LiOH. reaction 2.2 2LiOH(s) + CO2(g) → Li2CO3(s) + H2O(l) ∆H 2 ꝋ Calculate the mass of CO 2 that would be exhaled, in terms of kg/CM -d (kilograms per crewmember per day), using the information below. average volume of CO2 exhaled per breath = 25 cm3 number of breaths per minute = 15 density of CO2 at room temperature = 1.98 g dm−3 [2] (iv) Determine the maximum number of days that this mission can last before all the LiOH in the canisters are used up. Give your answer as a whole number.