DHS H2 Chem 2012 Prelim P3 QP

Name: Index Number: Class: DUNMAN HIGH SCHOOL Preliminary Examination Year 6 H2 CHEMISTRY 9647/03 Paper 3 Free Response 18 September 2012 2 hours Additional Materials: Data Booklet Graph Paper INSTRUCTIONS TO CANDIDATES Write your name, register number and class on this question paper and on the Cover Sheet provided. 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. Start each question on a fresh sheet of paper. A Data Booklet is provided. 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 work securely together with the Cover Sheet on top. · Hand in the question paper separately. The total marks for this paper is 80 marks. This question paper consists of 8 printed pages and 0 blank page. @DHS 2012 [Turn over

2 © DHS 2012 9647/03 [Turn over Answer any four questions. 1 The study of organic compounds includes the collection of kinetic data and thermodynamic data of the compounds. (a) The kinetics of the hydrolysis of the ester, CH 3CH2CO2CH3, may be investigated by the following method. CH3CH2CO2CH3 + H2O ® CH3CH2CO2H + CH3OH In a 1 dm3 mixture, 0.350 mol of the ester was hydrolysed by heating with water and using hydrochloric acid as catalyst. The following results were obtained. Time/s Concentration of CH3CH2CO2H/mol dm–3 0 0 340 0.105 680 0.185 1080 0.243 1440 0.278 (i) Suggest how the progress of this reaction may be followed in order to obtain the results as stated. (ii) By drawing a suitable graph using the data given above, show that the reaction is first order with respect to the ester. It has been found that the hydrolysis reaction is first order with respect to the hydrochloric acid. (iii) Deduce the units of the rate constant. (iv) State and explain the effect of a catalyst on the rate constant. (v) Using suitable bond energy values from the Data Booklet, calculate the ∆H for the hydrolysis of the ester. (vi) Given that the standard enthalpy change of reaction for the hydrolysis is +7.6 kJ mol –1, suggest a reason for the difference between this given value and the value that you have calculated in (a)(v). [11] (b) Hydrolysis of ester can be achieved in the biological system by enzymes known as esterase. Enzymes are proteins that catalysed a specific chemical transfo rmation in the biological system. Such enzymes are generally quaternary proteins. (i) Sketch and explain the graph showing how the rate of hydrolysis changes with increasing concentration of the ester. (ii) Explain the meaning of quaternary structure of proteins. (iii) List 2 other major functions of proteins in the body. (iv) Suggest and