PJC H2 Chem 2012 Prelim P2 QP

PIONEER JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION HIGHER 2 CANDIDATE NAME CT GROUP 1 1 INDEX NUMBER CHEMISTRY 9647/02 Paper 2 Structured 10 September 2012 2 hours Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your Centre number, index number and name on all work you hand in. 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 workings. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all questions. 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 Paper 2 1 / 12 6 / 12 2 / 9 7 / 9 3 / 15 4 / 7 Penalty sf units 5 / 8 Total / 72 This document consists of 19 printed pages.

© PJC 2012 9647/02/JC2 Prelim/2012 2 Answer all the questions in the spaces provided. 1 Planning (P) You are provided with solutions FA 1, FA 2 and FA 3. FA 1 and FA 2 are either 1.0 mol dm –3 nitric acid or 1.0 mol dm–3 ethanoic acid whereas FA 3 is 2.0 mol dm–3 sodium hydroxide. You are to plan an experiment that will enable you to identify FA 1 and FA 2 , and hence, calculate the enthalpy change of neutrali sation for the reaction between ethanoic acid and sodium hydroxide. You are provided with the following apparatus: a thermometer, a polystyrene cup, other common apparatus in the laboratory (a) State the independent and dependent variable s when determining the identity of each solution, FA 1 and FA 2. [1] Independent variable …………………………………………………………………… Dependent variable ……………………………………………………………………... (b) Plan an experiment to identify which of the two solutions, FA 1 and FA 2 , is 1.0 mol dm–3 nitric acid and which is 1.0 mol dm–3 ethanoic acid. Your plan must identify the acids solely based on the change in temperature. Mathematical processing of the temperature change is thus not required. Your plan should give a step by step description of the method including: · the apparatus used for measurement · appropriate volumes of reagents · how you would measure the various variables [3] ……………………………………………………………………………………............. ................................................................................................................................ ................................................................................................................................ ................................................................................................................................

© PJC 2012 9647/02/JC2 Prelim/2012 3 ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ……………………………………………………………………………………............. ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ……………………………………………………………………………………............. ................................................................................................................................ ................................................................................................................................ (c) Either a burette with 0.1 cm 3 interval or a measuring cylinder with 1 cm3 interval can be used to measure the volume of FA 3 required. It is known that the error (or uncertainty) that is associated with each reading when using a measuring cylinder with 1 cm3 interval is ±0.5 cm3, while that using a burette with 0.1 cm3 interval is ±0.05 cm3. Assuming that the volume of FA 3 measured is V cm3, calculate the maximum total percentage error (or uncertainty) in the measurement of the volume of FA 3, in terms of V, when using: (i) a measuring cylinder with 1 cm3 interval, (ii) a burette with 0.1 cm3 interval. [2]

© PJC 2012 9647/02/JC2 Prelim/2012 4 (d) Explain clearly how you could determine the identity of the acids using the difference in temperature rise in the experiment proposed in (b). [2] ……………………………………………………………………………………............. ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ (e) (i) Define the term standard enthalpy change of neutralisation. …………………………………………………………………………………….... ........................................................................................................................ ........................................................................................................................ (ii) Show the mathematical expression for the enthalpy change of neutralisation between ethanoic acid and sodium hydroxide, using the volumes proposed in (b). The temperature change measured in (b) should be represented by ∆T. [You may assume that 4.2 J of heat energy raised the temperature of 1 cm3 of any solution by 1oC.] [3]

© PJC 2012 9647/02/JC2 Prelim/2012 5 (f) A student suggests titrating FA 3 against FA 1 and FA 2 separately, using phenolphthalein as indicator, to ident ify two acids . Explain why this proposed method cannot work. [1] ……………………………………………………………………………………............. ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ [Total: 12] 2 Nitrogen dioxide, NO2 undergoes dimerisation to form dinitrogen tetraoxide, N2O4. 2NO2(g) ⇌ N2O4(g) (a) (i) Draw the dot-and-cross diagram of NO2. (ii) State the shape and bond angle of the O–N–O bond in NO2. Shape …………………………………………… Bond angle ……………………………………………

© PJC 2012 9647/02/JC2 Prelim/2012 6 (iii) Draw the dot -and-cross diagram of NO 2- ion. With reference to your answer in (a)(i) and (ii), suggest a bond angle of the O –N–O in NO2- ion, as compared to NO2. Explain your answer. …………………………………………………………………………………….. ..................................................................................................................... ..................................................................................................................... ..................................................................................................................... .............