PJC H2 Chemistry 2008 JC2 H2 Chemistry Prelims Paper 3

PIONEER JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION 2008 CHEMISTRY 9746/03 Higher 2 Paper 3 Free Response 11 September 2008 2 hours Additional Materials: Data Booklet Writing Paper Cover Page READ THESE INSTRUCTIONS FIRST Write your name, CT Group and index number in the spaces at the top of this page and every sheet of your scripts. 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. Answer any four questions. Write your answers on the writing papers provided. Begin each question on a fresh page. If there is no answer to any of the questions, a blank sheet of paper for each unanswered question with the question number(s) must still be submitted. 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 your work securely together with the Cover Page on top. Indicate clearly on the Cover Page the questions you have attempted. This document consists of 7 printed pages. [Turn Over

2 Answer any four questions. 1 (a) When a sample containing 2 moles of SO 2Cl2 is placed in a 2.0 dm 3 vessel at 30°C, it decomposes to SO2 and Cl2 as shown in the equation below. SO2Cl2(g) ⇌ SO2(g) + Cl2(g) ΔH negative At equilibrium, the total pressure of the mixture is determined to be 38.9 atm. (i) Assuming the gases behave ideally, ca lculate the number of moles of each gas present at equilibrium. [4] (ii) Hence, calculate the value of Kc, giving its units. [2] (iii) State Le Chatelier’s principle. [1] (iv) State and explain ho w the value of K c would change if there was an increase in temperature. [2] (b) The chlorides of sodium and silicon di ffer considerably in their physical and chemical properties. State and account for one difference in the (i) physical property (ii) chemical property of the two compounds, writing equations where appropriate. [6] (c) Propose a reaction scheme (in not more than 3 steps) for each of the following conversions. Give the reagent s and conditions, as well as the structures of the intermediate compounds formed. [5] (i) CH3CH2CH2NH2 from CH3CH2OH (ii) CH3COCH2OH from CH3CH=CH2 [Total: 20] 2 (a) (i) Define the term standard enthalpy change of neutralisation. [1] (ii) The table shows the standard ent halpy change of neutralisation when various acids are neutralised by sodium hydroxide. Acid Standard enthalpy change of neutralisation hydrochloric acid -57.3 kJ mol-1 nitric acid -57.3 kJ mol-1 ethanoic acid -55.2 kJ mol-1 Explain why the standard enthalpy c hange of neutralisation of ethanoic acid is different from the other two acids. [1]

3 (iii) In an experiment to determine the enthalpy change of reaction between ethylamine and hydrochloric acid, 35.0 cm 3 of 1.0 mol dm -3 ethylamine was mixed with 45.0 cm 3 of 2.0 mol dm -3 hydrochloric acid. The temperature of the mixture rose by 5.2°C. Calculate the standard enthalpy change of the above reaction. (Assume the heat capacity of all solutions to be 4.2 J K-1 g-1) [2] (b) Ethylamine, CH3CH2NH2, is a weak base with a base dissociation constant of 4.5 x 10 -4 mol dm -3 at 25° C. In an acid-base titration, 40.00 cm 3 of 0.10 mol dm -3 hydrochloric acid is slowly added from a burette to 20.0 cm 3 of 0.10 mol dm-3 of ethylamine solution. (i) Calculate the pH of 0.10 mol dm-3 ethylamine solution. [2] (ii) Calculate the volume of hydrochloric acid to be added to obtain a solution which is equally effective in resist ing pH changes on addition of small amount of acid or alkali. Hence, calculate the pH of this solution. [2] (iii) Using your answers to (i) and (ii), sketch the expected acid-base titration graph to indicate the essential pH changes for the titration described. Mark clearly where the end point o ccurs and suggest a suitable indicator for the titration. [4] (c) Arrange 4-methylphenylamine, phenylamine and ethylamine in the order of increasing basicity. Explain your answer. [3] (d) The common analgesic drug Paracetamol can be synthesised from 4-aminophenol. OHCH3COHNOHN H2 Paracetamol (i) Suggest the reagent and condition necessary for this synthesis. [1] (ii) Suggest why the corresponding ester is not formed in the synthesis. [1] (iii) Paracetamol forms different products wh en it is treated with aqueous sodium hydroxide under different conditions. Give the structural formulae of the products formed and state the conditions for the reaction with aqueous sodium hydroxide. [3] [Total: 20]

4 3 (a) Hydrogen peroxide reacts with acidified iodide ions to liberate iodine, according to the following equation: H2O2(aq) + 2H+(aq) + 2I-(aq) → 2H2O(l) + I2(aq) The rate of reaction can be measured by the increase in the concentration of iodine formed over time. The reaction was determined to be zero order with respect to hydrogen ions. The following results were obtained by varying the concentrations of hydrogen peroxide and iodide ions. Expt Initial [H 2O2(aq)] / mol dm-3 Initial [I-(aq)] / mol dm-3 Initial rate / mol dm-3 min-1 1 0.020 0.040 1.2 x 10-4 2 0.020 0.050 1.5 x 10-4 3 0.050 0.040 3.0 x 10-4 4 0.020 0.500 1.5 x 10-3 5 0.050 1.000 7.5 x 10-3 (i) Define the terms order of reaction and half-life. [2] (ii) Determine the order of the reaction wit h respect to the two reactants and write down the rate equation. [3] (iii) Calculate the rate constant, stating its units. [1] (iv) The half-life of hydrogen peroxide in experiment 4 was 9.2 min. Predict the half-life of hydrogen peroxide in experiment 5. [1] (b) An alternative method of investigating the rate of the above reaction can be conducted by titrating the iodine formed with sodium thiosulphate solution. (i) Suggest how the reaction can be quenched at specified time intervals. [1] (ii) Write an equation for the reaction between iodine and thiosulphate. [1] (c) Explain each of the following observations as fully as you can. (i) The boiling points of HCl, HBr and HI increase down the group. [2] (ii) The thermal stability of HCl, HBr and HI decrease down the group. [2]

5 (d) An organic compound P, C 10H11O2Br, does not react with aqueous sodium carbonate. P reacts slowly on heating with aqueous sodium hydroxide, followed by acidification to form an optically active compound Q, and an insoluble oil R, C 7H8O. R gives benzoic acid on oxidation. One mole of Q reacts with two moles of phosphorus pentachloride to give steamy fumes. Deduce the structures of compounds P, Q and R. Explain the chemistry of the reactions described, writing equations where appropriate. [7] [Total: 20] 4 (a) Solid magnesium amide, Mg(NH 2)2 decomposes when heated to form a high melting point solid, Mg3N2, and ammonia gas as the only products. (i) Construct a balanced eq