RI 2018 Prelim P3 QP

© Raffles Institution 2018 9729/03/S/18 [Turn Over RAFFLES INSTITUTION 2018 YEAR 6 PRELIMINARY EXAMINATION Higher 2 CHEMISTRY 9729/03 Paper 3 Free Response 20 September 2018 2 hours Candidates answer on separate paper. Additional Materials: Answer Paper Data Booklet READ THESE INSTRUCTIONS FIRST Do not open this question booklet until you are told to do so. Write your name, class and index number on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Section A Answer all questions. Section B Answer one question. Begin each question on a fresh sheet of paper. A Data Booklet is provided. Do not write anything in it. You are reminded of the need for good English and clear presentation in your answers. At the end of the examination, fasten all your work securely together, with the cover page on top. The cover page is found on page 14. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 13 printed pages and 1 blank page.

2 © Raffles Institution 2018 9729/03/S/18 [Turn Over Section A Answer all the questions in this section. 1 (a) In the aldol reaction, two carbonyl compounds react with each other in the presence of a base catalyst to form a hydroxy carbonyl compound. The aldol reaction between two ethanal molecules, in the presence of OH − ions, is shown below. (i) A mixture of ethanal and propanone was subjected to the aldol reaction. Apart from 3-hydroxybutanal, suggest three other possible products formed. Ignore stereoisomers in your answer. [2] To determine the kinetics of reaction 1, two experiments, I and II, were carried out and the graphs of the concentration of ethanal against time were plotted. The graphs on page 13 show the results of experiments I and II with [OH–] = 1.0 mol dm−3 and 2.0 mol dm−3 respectively. For (a)(ii) and (a)(iii), draw clearly any construction lines on the graphs on page 13. (ii) OH− ions act as catalyst in the aldol reaction. Using the graph for Experiment I, determine the order of reaction with respect to ethanal. Explain your reasoning. [2] (iii) By finding the initial rates, determine the order of reaction with respect to OH–. [2] (iv) Hence, write an overall rate equation for this reaction. [1] (v) With reference to Experiment I, calculate a value for the rate constant and state its units. [2] (b) A is an intermediate formed in reaction 1. In a separate reaction, A was used a s a nucleophile to react with an optically active sample of 2-bromobutane. The product formed was found to rotate plane polarised light. (i) Describe the mechanism of this reaction. In your answer, show relevant lone pairs and dipoles, and use curly arrows to indicate the movemen