2024 Prelims HCI H2 Chem P3 (QP)

This document consists of 25 printed pages and 1 blank page. HWA CHONG INSTITUTION C2 Preliminary Examination Higher 2 CANDIDATE NAME CT GROUP 2 3 S CENTRE NUMBER S INDEX NUMBER CHEMISTRY Paper 3 Free Response 9729/03 11 September 2024 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. If additional space is required, you should use the pages at the end of this booklet. The question number must be clearly shown. Section A Answer all questions. Section B Answer one question. A Data Booklet is provided. The use of an approved scientific calculator is expected, where appropriate. 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. No. of sheets of writing paper submitted (write 0 if none) For Examiner’s Use 1 / 20 2 / 19 3 / 21 Circle your option below 4 / 5 / 20 Deductions (s.f.) Deductions (units) Deductions (structures) Total / 80

2 © Hwa Chong Institution 2024 9729/03/C2 Preliminary Examination [Turn Over Section A Answer all questions in this section. 1 (a) Like Group 2 carbonates, Group 2 nitrates also undergo thermal decomposition according to the following equation: M(NO3)2(s) → MO(s) + 2NO2(g) + ½ O2 (g) H > 0 (i) Draw a dot -and-cross diagram showing the bonding in Mg(NO 3)2, clearly indicating any co-ordinate bonds it contains. [2] (ii) Explain why the temperature for thermal decomposition of Group 2 nitrates increases down the group. [2] (iii) Deduce, with reasoning, the sign of the entropy change of the reaction. Hence, suggest why high temperature is needed for thermal decomposition to take place. [2] (iv) Using Table 1.1 and data from the Data Booklet, draw a Born-Haber cycle to calculate a value for the lattice energy of MgO. Show your working. Table 1.1 Ho / kJ mol –1 1st electron affinity of oxygen –142 2nd electron affinity of oxygen +844 standard enthalpy change of atomisation of Mg(s) +148 standard enthalpy change of formation of MgO(s) –602 [4] ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….……………………………………………… ……………………………………………………….………………………………………………

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4 © Hwa Chong Institution 2024 9729/03/C2 Preliminary Examination [Turn Over (b) Describe the reactions, if any, of the oxides MgO, A l2O3 and P4O10 with water. Write equations for any reaction and state the pH of the resultant mixtures. [3] ..……………………………..……………….……………………………………………………...…...… ..……………………………..……………….……………………………………………………...…...… ..……………………………..……………….……………………………………………………...…...… ..……………………………..……………….……………………………………………………...…...… ..……………………………..……………….……………………………………………………...…...… ..……………………………..……………….……………………………………………………...…...… ..……………………………..……………….……………………………………………………...…...… ..……………………………..……………….……………………………………………………...…...… ..……………………………..……………….……………………………………………………...…...… ..……………………………..……………….……………………………………………………...…...… ..……………………………..……………….……………………………………………………...…...… ..……………………………..……………….……………………………………………………...…...… ..……………………………..……………….……………………………………………………...…...… ..……………………………..……………….……………………………………………………...…...… ..……………………………..……………….……………………………………………………...…...… (c) In the presence of A lCl3, methylbenzene can undergo electrophilic substitution with halogens like chlorine. (i) Explain why AlCl3 can act as a Lewis acid. [1] (ii) Draw the structures of the major organic products formed in the electrophilic substitution reaction between methylbenzene and chlorine. [1] (iii) Write a balanced equation for the reaction between methylbenzene and hot acidified potassium manganate(VII). Use [O] to represent the oxidising agent. [1] If the halogen is changed to iodine, electrophilic substitution of methylbenzene occurs much less readily. To increase its reactivity, reagents like iodine monochloride, ICl, in the presence of AlCl3 are used instead. (iv) Explain why ICl is more reactive in the electrophilic substitution of methylbenzene compared to I2. [1] (v) Draw the mechanism of the reaction between methylbenzene and ICl, showing the formation of the electrophile and any intermediates. Use curly arrows to indicate the movement of electron pairs, and show any relevant lone pairs. [3]

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