RI H2 CHEM P2 Prelim

© Raffles Institution 9647 / 2011 H2 Chemistry Pape r 2 [Turn Over RAFFLES INSTITUTION 2011 YEAR 6 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS INDEX NUMBER CHEMISTRY 9647/02 Paper 2 Structured Questions 19 September 2011 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, class and index number in the spaces provided at the top of this page. Write in dark blue or black pen in the spaces provided. 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 all questions. A Data Booklet is provided. Do not write anything on it. 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. For Examiner’s Use 1 / 12 2 / 20 3 / 15 4 / 12 5 / 13 Total / 72 This document consists of 16 printed pages.

2 © Raffles Institution 9647 / 2011 H2 Chemistry Pape r 2 [Turn Over 1 Planning (P) You are to design an experiment to determine the id entity of a soluble metal sulfate, MSO 4, by using a gravimetric method. A solid sample con taining MSO 4, with some carbonate and sulfite impurities, is provided. You may assume that the following are available: • 1.0 g of the solid sample of MSO 4, of a known percentage purity • 0.50 mol dm –3 aqueous barium chloride, BaC l2 • concentrated hydrochloric acid, HC l • 250 cm 3 and 500 cm 3 beakers • weighing bottle • measuring cylinders • glass rod • filter paper • filter funnel • deionised water • infra-red lamp You may also assume that standard laboratory apparatus are available. (a) Write an ionic equation, including state symbols, f or the reaction between the unknown metal sulfate and aqueous barium chloride. ………………………………………………………………………………………….. [1] (b) Explain why concentrated hydrochloric acid should b e added to the impure metal sulfate. ......…………………………..……………………………………………………………… ......…………………………..……………………………………………………………… ......…………………………..……………………………………………………………… ......…………………………..……………………………………………………………… ………………………………………………………………………………………….. [2] (c) Using your answers to (a) and (b) , outline a sequence of steps in which the experiment should be carried out to determine the i dentity of MSO 4. You should state clearly the measurements to take and any assumption(s) made. [Treatment of results is not required.] For examiner’s use

3 © Raffles Institution 9647 / 2011 Y ear 6 Preliminary Examinations Paper 2 [Turn Ove r

4 © Raffles Institution 9647 / 2011 H2 Chemistry Pape r 2 [Turn Over ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. …………………………………………………………………………………… ………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………… ……………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ………… …………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. …………………………………………………………………………………………… ………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. For examiner’s use

5 © Raffles Institution 9647 / 2011 H2 Chemistry Pape r 2 [Turn Over ………………………………………………… …………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. …………… ………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………… … [7] (d) A 0.892 g impure solid sample of the unknown metal sulfate, M SO 4, reacted with excess acidified aqueous barium chloride to form 1.049 g of barium sulfate. Given that the sample contained 80.4% by mass of metal su lfate, determine the identity of the unknown metal sulfate. The unknown metal sulfate is ………………………………………… [2] [Total: 12] For examiner’s use

6 © Raffles Institution 9647 / 2011 H2 Chemistry Pape r 2 [Turn Over 2 The rate of reaction of bromine with bromopropanone was studied in acid solution at 25 °C. The table gives some results (repeated on page 6) obtained for the reaction CH 3COCH 2Br + Br 2 → CH 3COCHBr 2 + HBr initial concentration / mol dm – 3 [Br 2] at specified times / mol dm – 3 Expt bromopropanone hydrochloric acid 0 s 1500 s 30 00 s 4500 s 1 0.050 0.50 0.050 0.036 0.025 0.019 2 0.050 0.50 0.100 0.086 0.076 0.068 3 0.020 0.50 0.050 0.044 0.038 0.034 The reaction may be followed by either chemical or physical methods of analysis. Sampling & Titration In each of the above experiments, the reagents were mixed and then three samples were successively withdrawn, at appropriate times, as the reaction proceeded. At 1500 s, ice-cold water was added to the first sampl e. To this, excess aqueous potassium iodide was added. The resultant solution was then titrated against standard sodium thiosulfate solution. This procedure was rep eated with the second and third samples, with ice-cold water being added at 3000 s and 4500 s respectively. (a) (i) Why was ice-cold water added? ..…… ………………………..………………………………………………………. ..……………………………..………………………………………………………. (ii) Suggest why aqueous sodium hydroxide should not be used in place of ice-cold water. ..……………………………..………………………………………………………. ..……………………………..……………………… ………………………………. (ii i) Write an ionic equation to show the reaction involving potassium iodide. ..……………………………..………………………………………………………. (i v) Suggest why an indicator was not needed for the titration. ..……………………………..………………………………………… ……………. …………………………………………………………………………………… [4] (b) Suggest how the above reaction could be followed by a physical method of analysis. .…..………………………… ..………………………………………………………… …… ………………………………………………………………………………………….. [1] For examiner’s use H+

7 © Raffles Institution 9647 / 2011 H2 Chemistry Pape r 2 [Turn Over The rate equation for the reaction is rate = k [Br 2] a [CH 3COCH 2Br] b [H +] (c) (i) The orders of reaction with respect to Br 2 and CH 3COCH 2Br are to be determined. Use the data below (repeated from page 5) to plot suitable graphs on the grid given below. initial concentration / mol dm – 3 [Br 2] at specified times / mol dm – 3 Expt bromopropanone hydrochloric acid 0 s 1500 s 30 00 s 4500 s 1 0.050 0.50 0.050 0.036 0.025 0.019 2 0.050 0.50 0.100 0.086 0.076 0.068 3 0.020 0