RI H2 Chem 2013 Prelim P3 QP

-1- RAFFLES INSTITUTION 2013 YEAR 6 PRELIMINARY EXAMINATION Higher 2 CHEMISTRY 9647/03 Paper 3 Free Response 24 September 2013 Candidates answer on separate paper. 2 hours Additional Materials: Writing 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 in the spaces provided on the cover page. 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. Answer any four questions. Begin each question on a fresh sheet of paper. A Data Booklet is provided. Do not write anything on it. You are reminded of the need for good English and clear presentation in your answers. The number of marks is given in brackets [ ] at the end of each question or part question. At the end of the examination, fasten all your work securely together, with the cover page on top. This document consists of 14 printed pages. 212

-2- Answer any four questions. Begin each question on a fresh sheet of paper. 1 Esters are sweet -smelling organic compounds that have been used as flavourings in food and perfumes. For example, ethyl propanoate is an ester with pineapple-like smell. (a) Explain why the rate of t he following reaction gradually increases at first and then decreases. CH3CH2COOCH2CH3 + H2O  CH3CH2COOH + CH3CH2OH ethyl propanoate [2] (b) The kinetics of the hydrolysis of ethyl propanoate in the presence of aqueous sodium hydroxide solution at T K was studied. Two separate experiments were carried out with different concentrations of aqueous sodium hydroxide solution. For each experiment, the concentration of ethyl propanoate was determined at regular time intervals as the reaction progressed. The graph on page 13 shows the results of Experiment 1 with [NaOH] = 2.0 mol dm3. The results of Experiment 2 with [NaOH] = 1.0 mol dm3 are shown below. Time / min Experiment 2 with [NaOH] = 1.0 mol dm3 [CH3CH2COOCH2CH3] / mol dm3 0 0.0200 25 0.0152 50 0.0115 75 0.0088 100 0.0067 125 0.0051 1 (i) Using the same axes on page 13, plot the graph for Experiment 2. 3 (ii) Use the two graphs to determine the order of reacti on with respect to CH3CH2CO2CH2CH3 and to NaOH, showing your working clearly. 1 (iii) Hence write the rate equation for the above reaction. 2 (iv) Calculate the initial rate from E xperiment 1, and use it, together with your rate equation, to calculate the rate constant for the reaction. 1 (v) In a thi