SAJC Prelim P2 QP

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] …………………………………………………………………………………………………. …………………………………………………………………………………………………. (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] …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. (ii) Based on the diagram above, suggest why the sign of ∆S is negative for the reaction. [1] …………………………………………………………………………………………. …………………………………………………………………………………………. glucose gluconic acid glucose O2 glucose O2 GOx

3 [Please Turn Over 1 (b) (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] [glucose] rate

4 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 mol dm−3 initial [GOx] = 1.00 x 10−2 mol dm−3 initial [O2] = 1.00 x 10−2 mol dm−3 The following results in Table 1 were obtained. Table 1 t/s [glucose] / mol dm −3 0 5.00 x 10 −3 10 3.40 x 10 −3 20 2.50 x 10 −3 30 1.80 x 10 −3 60 6.00 x 10 −4

5 [Please Turn Over 1 (d) (i) To determine the order of reaction with respect to [glucose], use these data to plot a suitable graph on the grid below. [2] (ii) Hence, deduce the order of reaction with respect to [glucose], showing all your working and drawing clearly on your graph. [2] …………………………………………………………………………………………. …………………………………………………………………………………………. ………………………………………………………………………………………….

6 1 (d) (iii) In the second and third investigations, the concentrations of oxygen and GOx were changed, but the initial [glucose] was kept the same as before. The following results in Table 2 were obtained. Table 2 Investigation Initial [O 2] (mol dm−3) Initial [GOx] (mol dm−3) Initial rate (mol dm−3 s−1) 1 1.00 x 10 −2 1.00 x 10 −2 Y 2 5.00 x 10 −3 1.00 x 10 −2 2.00 x 10 −4 3 5.00 x 10 −3 2.50 x 10 −3 5.00 x 10 −5 Use your graph in (d)(i) to determine the initial rate Y, showing all your working and drawing clearly on your graph. Hence, use the information in Table 2 to determine the orders of reaction with respect to [O 2] and [GOx]. Explain your reasoning. [3]

7 [Please Turn Over 1 (e) GOx can be used in a biosensor to convert glucose present in body fluids into gluconic acid. The amount of hydrogen peroxide produced is then reduced electrochemically to determine the amount of glucose present. A 0.1 cm 3 of blood sample from a patient was tested to diagnose if he was at risk of diabetes. The diagnosis is based on the concentration of glucose in the blood. Condition [glucose] in blood (x 10 −3 mol dm−3) Normal less than 5.6 Pre-diabetes 5.6 − 6.9 Diabetes More than 6.9 The biosensor gave a current of 1.01 mA for 1 min. (1000 mA = 1A) (i) Calculate the number of moles of hydrogen peroxide produced. Hence, diagnose the condition of the patient. [3] (ii) Before the test, the blood sample has to be treated to remove some components present. Suggest why a treated blood sample was necessary for the biosensor to give an accurate reading. [1] …………………………………………………………………………………………. …………………………………………………………………………………………. [Total: 19]

8 2 This question deals with carbon and silicon which are both elements in Group 14. (a) C60 and diamond are allotropes of carbon. C 60 is a simple covalent molecule while diamond is a giant covalent molecule. State the type of bonding and describe the lattice structure of solid C60. C60 [2] …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. (b) 0.144 g of C 60 was placed in a 100 cm3 container of hydrogen gas at 20 °C and 1.00 × 105 Pa. The reaction occurred as shown in the equation. C60 (s) + xH2 (g) → C60H2x (s) When all the C60 had reacted, the pressure was found to be 2.21 × 10 4 Pa at the same temperature. (i) Calculate the amount, in moles, of C60 that reacted. [1]

9 [Please Turn Over 2 (b) (ii) Calculate the amount, in moles, of hydrogen gas that reacted with C60. [2] (iii) Use your answers from (i) and (ii) to deduce the molecular formula of the hydrocarbon, C 60H2x. [2] (c) (i) Graphite is another allotrope of carbon. State the type of hybridisation and draw the arrangement of the hybrid orbitals about each C atom. [2] (ii) Graphite is a good conductor of electricity. Explain, with reference to orbital overlap, how graphite has a high electrical conductivity. [2] …………………………………………………………………………………………. …………………………………………………………………………………………. ………………………………………………………………………………………….

10 2 (c) (iii) The values for the enthalpy change of combustion of graphite and diamond are given in the table below. Substance Enthalpy change of combustion / kJ mol −1 Graphite −394 Diamond −396 The products of the combustion reactions of graphite and diamond are carbon dioxide and water. Suggest why the enthalpy change of combustion of graphite is less exothermic than that of diamond. [1] …………………………………………………………………………………………. …………………………………………………………………………………………. (d) Silicon is another element in Group 14 which shows the same kind of bonding and structure as diamond. (i) When silicon reacts with magnesium, Mg 2Si forms. Mg2Si is thought to contain the Si4– ion. Compare and explain the difference between the atomic and anionic radii of silicon. [2] …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………..