2021 EJC Prelims Paper 3 QP

© EJC [Turn Over EUNOIA JUNIOR COLLEGE JC2 Preliminary Examination 2021 General Certificate of Education Advanced Level Higher 2 CANDIDATE NAME CIVICS GROUP 2 0 – INDEX NUMBER CHEMISTRY Paper 3 Free Response 9729/03 22 September 2021 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 32 printed pages.

2 © EJC 9729/03/J2PE/21 Section A Answer all the questions in this section. 1 Halogens are powerful oxidising agents, and the oxidising power of halogens may be understood via the energy cycle in Fig. 1.1. Fig. 1.1 The corresponding values of some of the energy terms are given in Table 1.1. Table 1.1 energy term I (kJ mol–1) energy term II (kJ mol–1) energy term III (kJ mol–1) F +79 –328 –506 Cl +121 –349 –364 Br +112 –324 –335 I +107 –295 –293 (a) (i) Name the three energy terms, I, II and III. [2] (ii) Explain why energy term I becomes less endothermic moving down the group from chlorine to iodine. [1] (iii) Explain the exceptionally low value for energy term I of fluorine, in contrast to that of the remainder of the halogens. [1] (iv) Explain why energy term II becomes less exothermic moving down the group from chlorine to iodine. [1] (v) Using values from the Data Booklet, account for the difference in the value s of energy term III. [2] ................................ ................................ ................................ ........................... ................................ ................................ ................................ ........................... ................................ ................................ ................................ ........................... ................................ ................................ ................................ ........................... I II III Hr

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4 © EJC 9729/03/J2PE/21 Alanine, which is found in a variety of food sources, is an amino acid that can be derived from propanoic acid. One of the methods to obtain alanine from propanoic acid is illustrated in the pathway below. (b) (i) Outline the mechanism for the formation o f 2 -bromopropanoic acid via the reaction between propanoic acid and bromine gas. [3] (ii) In the reaction between propanoic acid and bromine gas, the relative rate of abstraction of primary, secondary and tertiary hydrogen is in the ratio of 2 : 3 : 6. Draw the structures of all mono -brominated products formed, including stereoisomers if any, and state their relative proportion. [3] (iii) With reference to (b)(i) and using relevant values from the Data Booklet, explain why free radical substitution is rarely performed to produce 2-iodopropanoic acid. [2] (iv) State the reagents and conditions for the formation of alanine, CH3CH(NH2)CO2H, from 2-bromopropanoic acid. [1] ................................ ................................ ................................ ........................... ................................ ................................ ................................ ........................... ................................ ................................ ................................ ........................... ................................ ................................ ................................ ........................... ................................ ................................ ................................ ........................... ................................ ................................ ................................ ........................... ................................ ................................ ................................ ........................... ................................ ................................ ................................ ...............