2024 JPJC Chem Prelim P3 QP

© Jurong Pioneer Junior College [Turn Over NAME CLASS 23S JURONG PIONEER JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION 2024 CHEMISTRY 9729/03 Higher 2 Paper 3 Free Response 12 September 2024 2 hour Candidates answer on the Question paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, class and index number in the spaces at the top of this page. 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. 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. Section A Answer all questions. Section B Answer one question. Write the Question number of the Question you have attempted, in the box provided below. A Data Booklet is provided. The use of an approved scientific calculator is expected, where appropriate. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 2 3 4 or 5 Penalty (delete accordingly) Lack 3sf in final answer –1 / NA Missing/wrong units in final ans –1 / NA Bond linkages –1 / NA Total 80 This document consists of 32 printed pages inclusive of 1 blank page.

2 © Jurong Pioneer Junior College 9729/03/J2 PRELIMINARY EXAM/2024 Section A Answer all the questions in this section. 1 (a) One version of the Fischer -Tropsch process for manufacturing methane is the reaction of carbon monoxide with hydrogen. CO(g) + 3H2(g) ⇌ CH4(g) + H2O(g) H210 kJ mol-1 A mixture of CO and H2 in a 1:3 molar ratio was added into a sealed vessel and heated to 1200K. At equilibrium, 40% of the CO had reacted. The total pressure in the vessel was 12 atm at equilibrium. For Examiner’s Use (i) Write the expression for the equilibrium constant, Kp, for this reaction. [1] (ii) Use your expression to calculate the value of Kp for the reaction at 1200K. Include its units. [3] (iii) Given that the value of Kp decreases with increasing temperature, deduce the sign for the enthalpy change, H of the forward reaction. Explain your reasoning. [1] ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. …………………………………………………………………………………….

3 © Jurong Pioneer Junior College 9729/03/J2 PRELIMINARY EXAM/2024 [Turn Over ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. For Examiner’s Use (b) Describe and explain how the entropy of each of the following systems will change during the stated process. • 1 mol of N2(g) at 298K is added to 1 mol of CH4(g) at 298K. • 1 mol of Cl2(g) at 298 K is heated to 373 K. Assume the pressure of each gas remains at 1 atm throughout and no reaction occurs between N2 and CH4. [2] …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… ……………………………………………………………………………………………

4 © Jurong Pioneer Junior College 9729/03/J2 PRELIMINARY EXAM/2024 (c) (i) During the monobromination of pentane, three different bromoalkanes are formed as shown in Fig. 1.1. Br Br Br + + 1-bromopentane 2-bromopentane 3-bromopentane Fig. 1.1 Predict the expected theoretical ratio in which these three products would form if the monobromination of pentane occurs randomly. Explain your answer. [2] For Examiner’s Use (ii) When the monobromination was practically carried out in an experiment , the percentage of 1-bromopentane was obtained in the lowest proportion. Suggest an explanation for the difference between this experimental result and what you predicted in (c)(i). [1] ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. (d) The Wurtz reaction below shows two iodoalkanes react with Na in dry ether, to form a new carbon−carbon bond, resulting in the formation of a new alkane. R−I + R’−I + 2Na → R−R’ + 2NaI Reaction of a single iodoalkane, RI, with Na metal in dry ether via Wurtz reaction will give a good yield of symmetrical alkane product. Draw the organic product formed when (iodomethyl)benzene reacts with Na metal in dry ether. (iodomethyl)benzene [1]

5 © Jurong Pioneer Junior College 9729/03/J2 PRELIMINARY EXAM/2024 [Turn Over …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… For Examiner’s Use (e) Bromoalkanes and alkoxides react in the Williamson ether synthesis to form the ether functional group containing C-O-C, an example of which is shown below. RBr + R’O− → ROR’ + Br− alkoxide ether It is known that S N2 mechanism is usually undergone in Williamson ether synthesis. Suggest the structures of the halogenoalkane and alkoxide ion RO− you would use to synthesise the ether below, using the Williamson synthesis method. O [1] …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… ……………………………………………………………………………………………

6 © Jurong Pioneer Junior College 9729/03/J2 PRELIMINARY EXAM/2024 (f) (i) CH3OCH3, methoxymethane is the simplest ether which is used as aerosol propellants. Given that CH3OCH3, contains C -O-C bond , draw the ‘dot-and-cross’ diagram for CH3OCH3. Use VSEPR (valence shell electron pair repulsion) theory to describe and explain the shape about the oxygen and suggest the C-O-C