2022 JPJC JC2 H2 Chem Prelim P3 Suggested Answers

© Jurong Pioneer Junior College [Turn Over NAME CLASS 21S JURONG PIONEER JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION 2022 CHEMISTRY 9729/03 Higher 2 Paper 3 Free Response Questions 19 September 2022 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. Write in dark blue or black pen on both sides of the paper. 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 end of this booklet. The question number must be clearly shown. Answer all questions in Section A. Answer 1 question in Section B. 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 1 21 2 20 3 19 4 or 5 20 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 31 printed pages inclusive of 1 blank page.

2 © Jurong Pioneer Junior College 9729/03/J2 PRELIMINARY EXAM/2022 Section A Answer all the questions in this section. 1 (a) Bromoethane reacts with “acetylide” anion, CH3C≡C:− to form new carbon−carbon bonds. This reaction takes place in two steps. In step 1, an acid-base reaction occurs. CH3C≡C:− is formed from the reaction of propyne and a strong base, sodium amide, NaNH2. step 1: CH3C≡CH + :NH2− → CH3C≡C:− + NH3 In step 2, the intermediate anion reacts with bromoethane to form the product. step 2: CH3CH2Br + CH3C≡C:− → CH3CH2C≡CCH3 + Br− For Examiner’s use Name and suggest the mechanism for step 2. Show relevant dipoles, using curly arrows to indicate the movement of electron pairs. Type of mechanism: nucleophilic substitution [3] (b) 4-bromopentanol can be used to synthesise Compound C by the three -step route shown in Fig. 1.1. Br OH O O A B C step 1 step 2 step 3 4-bromopentanol Fig. 1.1 State the structures for compounds A and B, and reagents and conditions for steps 1, 2 and 3 in this route. [4] step 1 : NaCN (or KCN), ethanol, heat (✓) step 2 : H2SO4(aq) (or HCl(aq)), heat (✓)

3 © Jurong Pioneer Junior College 9729/03/J2 PRELIMINARY EXAM/2022 [Turn Over step 3 : concentrated sulfuric acid, heat(✓) (c) Describe and explain the relative ease of hydrolysis of the following three chlorine-containing compounds. . [3] Ease of hydrolysis of C6H5Cl < C6