YIJC 2025 Prelim P3 (for exchange)_H2 Chem

©YIJC 9729/03/JC2/PE/2025 [Turn over YISHUN INNOVA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CG INDEX NO CHEMISTRY Paper 3 Free Response Candidates answer on the Question Paper. Additional Materials: Data Booklet 9729/03 16 September 2025 2 hours 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 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 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. This document consists of 28 printed pages. For Examiner’s Use Section A 1 / 17 2 / 18 3 / 25 Section B 4 or 5 / 20 Penalty units significant figures Overall / 80

©YIJC 9729/03/JC2/PE/2025 2 Section A Answer all the questions in the spaces provided. 1 (a) Explain, with the aid of a labelled Boltzmann distribution diagram, the effect on a rate constant of increasing temperature from T1 to T2. [3]

3 ©YIJC 9729/03/JC2/PE/2025 [Turn over (b) Hydrogen bromide, HBr, undergoes addition reaction with alkenes. With but-1-ene, 2-bromobutane is produced rather than 1-bromobutane. (i) Draw a mechanism for this reaction and use it to explain the preferential production of 2-bromobutane. [3] (ii) Using the mechanism, write the rate equation for this reaction. [1] (iii) Sketch a graph to show how the rate of reaction varies with the concentration of but -1-ene when hydrogen bromide is in excess. Explain your answer. [2]

©YIJC 9729/03/JC2/PE/2025 4 (c) But-2-ene is a positional isomer of but-1-ene. But-2-ene occurs in two isomeric forms, A and B. (i) Explain how A and B are stereoisomers of each other but but -1-ene does not show stereoisomerism. [2] (ii) Describe a chemical test, with appropriate observations, that could distinguish between but-1-ene and but-2-ene. [2] (d) But-1-ene can be converted into an ether (–C–O–C–) via the steps shown in Fig. 1.1. Fig. 1.1 In step 1, an epoxide functional group is formed when a n O atom adds across the double bond through reaction with m-CPBA. In step 2, t he epoxide formed reacts with sodium methoxide, a nucleophile , to form an ether functional group (–C–O–C–).

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