SAJC Prelim_P2_Answers

NAME Class ST ANDREW’S JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION Chemistry (9729) Paper 2 Structured Questions 12 September 2018 2 hours Additional Materials: Data Booklet READ THESE INSTRUCTIONS: 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. 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: Question 1 2 3 4 5 Total Marks 19 20 10 7 19 75 This document consists of 20 printed pages (including this page).

2 GOx Answer all the questions. 1 Glucose oxidase (GOx) is an enzyme found in certain species of insects and fungi that catalyses the oxidation of glucose to gluconic acid. C6H12O6 + O2 + H2O C6H12O7 + H2O2 (a) Write two half-equations to show that this is a redox reaction. [2] C6H12O6 + H2O  C6H12O7 + 2H+ + 2e─ O2 + 2H+ + 2e─  H2O2 (b) The binding of reactants to GOx can be simplified with a diagram as shown below. (i) Explain why GOx can be described as a biological catalyst. [2] GOx allows certain reactants to bind specifically to it for the conversion into products. GOx speeds up the rate of reaction by providing an alternative pathway of lower activation energy. OR It is regenerated / remained chemically unchanged at the end of the reaction. (ii) Based on the diagram above, suggest why the sign of ∆S is negative for the reaction. [1] The 2 reactants and GOx must come together to form one large entity. OR There is a decrease in number of (gaseous) particles. Hence, the products are less disordered than the reactants. glucose gluconic acid glucose O2 glucose O2 GOx

3 [Please Turn Over (iii) Sketch a graph showing how the rate of this GOx-catalysed reaction varies with the concentration of glucose. [1] (c) The overall equation can be re-expressed to show the change in functional group. C 5H11O5CHO + O2 + H2O C 5H11O5COOH + H2O2 glucose gluconic acid Calculate the enthalpy change of reaction for the conversion of glucose into gluconic acid. Use relevant data from the Data Booklet. [2] Bonds broken in reactant: C─H, C=O, O=O, 2O─H Bonds formed in product: C=O, C─O, O─H + 2O─H + O─O ∆H = (410 + 496) − (360 + 460 + 150) = − 64.0 kJ mol−1 (d) Experiments were done to determine the kinetics of the reaction. In the first investigation, the following reaction mixture was prepared. initial [glucose] = 5.00 x 10−3