2024 Prelims EJC H2 Chem P3 (QP)

© EJC [Turn Over EUNOIA JUNIOR COLLEGE JC2 Preliminary Examination 2024 General Certificate of Education Advanced Level Higher 2 CANDIDATE NAME CIVICS GROUP 2 3 – INDEX NUMBER CHEMISTRY Paper 3 Free Response 9729/03 12 September 2024 2 hours Candidates answer on the Question Paper Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, civics group, index number 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 addition 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 the questions Section B Answer one question. 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 Paper 3 Section A 1 / 20 2 / 20 3 / 20 Section B 4 / 20 5 / 20 Total / 80 This document consists of 31 printed pages and 1 blank page.

2 © EJC 9729/03/J2PE/24 BLANK PAGE

3 © EJC 9729/03/J2PE/24 [Turn Over Section A Answer all the questions in this section. 1 Alkenylbenzene molecules are secondary plant metabolites with certain levels of toxicity, despite their presence in herbs and spices . One type of alkenylbenzene is (2-ethylethenyl)benzene. (a) (2-ethylethenyl)benzene exhibits stereoisomerism and exists as a pair of stereoisomers L and M. The structure of M is as shown. (i) State the type of stereoisomerism exhibited by (2-ethylethenyl)benzene. [1] (ii) Draw the skeletal structure of L. [1] (iii) Draw the structure of a constitutional isomer of M that fulfils the following criteria: • does not exhibit the stereoisomerism stated in (a)(i) • has a non-terminal alkene [1] ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ .............................

4 © EJC 9729/03/J2PE/24 (b) When a pure sample of L is left to stand, a portion of it converts to M. The mixture will then eventually achieve equilibrium, as illustrated in the following equation. L  M Fig. 1.1 shows a sketch of how the Gibbs free energy of the mixture of L and M varies with the composition of the mixture at a particular temperature. The slope of the graph at each point corresponds to G of the conversion of L to M. Fig. 1.1 (i) Given that the Kc value of this equilibrium at the temperature given is 5.25, calculate the equilibrium concentration of L when 1.30 mol dm –3 of pure L was placed in an empty reaction chamber and allowed to reach equilibrium. [2] (ii) Label Fig. 1.1 with a cross (×) to show the composition of the mixture of L and M at equilibrium. [1] (iii) With reference to the structures of L and M, explain why the minimum point of the graph in Fig. 1.1 lies closer to the point of pure M. [1] ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. Gibbs free energy, G pure M (standard state) pure L (standard state) composition of mixture Gibbs free energy, G

5 © EJC 9729/03/J2PE/24 [Turn Over ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. (c) An attempt to synthesise N by mixing one mole of M with two moles of Br 2 in the presence of anhydrous FeBr3 in the dark, was not successful. (i) Draw the skeletal structure of the major product obtained instead. [1] (ii) A trace amount of P was obtained as a by-product. Suggest how P was formed during the reaction. [1]

6 © EJC 9729/03/J2PE/24 The student then changed M to Q and changed the amount of Q and Br2 used to one mole each, while keeping the other conditions the same . This caused the student to obtain R, the 4-bromo product, as the major product, as shown