SRJC H2 Chem 2012 Prelim P2 QP

1 SERANGOON JUNIOR COLLEGE General Certificate of Education Advanced Level Higher 2 CANDIDATE NAME CLASS CHEMISTRY 9647/02 Preliminary Examination 17 August 2012 Paper 2 Structured Questions (SPA) 2 hours Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and class on all the 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 work. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all questions in the space provided. A Data Booklet is provided. At the end of the examination, fasten all your work securely together. The number of marks is given in the brackets [ ] at the end of each question or part questions. For Examiner’s Use P1 /40 P2 /72 P3 /80 GRAND /192TOTAL % GRADE For Examiner’s Use 1(P) /12 2 /8 3 /18 4 /10 5 /12 6 (P) /12 TOTAL /72 P2 This document consist of 16 printed pages and 0 blank page SRJC PRELIM 9647 P2 Turn Over]

2 SRJC PRELIM 9647 P2 Turn Over] 1 (a) Planning In the presence of hydrogen ions , bromate(V) ions, BrO 3–, oxidise bromide ions to bromine. BrO3– (aq) + 5Br – (aq) + 6H+ (aq) ¨ 3Br2 (aq) + 3H2O (l) The reaction is relatively slow and can be followed by adding aqueous phenol and the indicator methyl orange to the reaction mixture. As bromine is formed, it reacts rapidly with the phenol present until the latter is used up. The free bromine in solution now bleaches the methyl orange indicator. The initial rate of the reaction can be investigated by measuring the time taken for the methyl orange indicator to be bleached. You are to plan a series of experiments to determine the order of reaction with respect to the bromide ion. In addition to the standard apparatus present in a laboratory, you are provided with the following: FA 1 0.01 mol dm – 3 aqueous KBr. FA 2 1.0 mol dm– 3 potassium bromate(V), KBrO3. FA 3 1.0 mol dm– 3 sulfuric acid, H2SO4. Aqueous phenol containing methyl orange indicator Distilled water For Examiner’s Use (i) Complete the table below and outline, by means of a series of numbered steps, · the apparatus to be used · the experimental procedure · the measurements to be taken to collect the required data. Expt . Volume of phenol/methyl orange indicator solution / cm3 Volume of FA1 / cm3 Volume of FA2 / cm3 Volume of FA3 / cm3 Volume of distilled water / cm3 1 20.0 50.0 50.0 20.0 0.0 2 20.0 40.0 3 20.0 30.0 4 20.0 20.0 5 20.0 10.0

3 SRJC PRELIM 9647 P2 Turn Over] Outline of experiment: …………………………………………………………………………………………………….… ………………………………………………………………………………………………….…… …………………………………………………………………………………………………….… ……………………………………………………………………………………………….……… …………………………………………………………………………………………. …… …….. …………………………………………………………………………………………. …… …….. …………………………………………………………………………………………. …… …….. …………………………………………………………………………………………….……….. …………………………………………………………………………………………. …… ……... …………………………………………………………………………………………..…… …….. For Examiner’s Use (ii) In order to find the order of reaction with respect to bromide, a graph of log 10( 1 t ) against log10(volume of K Br (aq)) can be plotted. Use the general rate equation to derive a relationship between log10( 1 t) and log10(volume of KBr (aq)). Hence, explain how the order of reaction with respect to bromide can be found from the plotted graph. (iii) The concentration of phenol used in the experiment is very low. Suggest why this is so. ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… [7]

4 SRJC PRELIM 9647 P2 Turn Over] (b) An experiment was carried out to measure the enthalpy change for the react ion of zinc with aqueous copper(II) sulfate. The equation for the reaction is: Zn (s) + CuSO4 (aq) ¨ ZnSO4 (aq) + Cu (s) · A measuring cylinder was used to transfer separate 50 cm 3 samples of 1.25 mol dm-3 copper(II) sulfate solution into polystyrene cups. · Different weighed amounts of zinc powder were added to each sample of copper(II) sulfate. · Each mixture was stirred thoroughly and the temperature rise noted. The results of the experiment is summarised on the graph below. For Examiner’s Use (i) Explain the shape of the graph. ……………………………………………………………………………… … ………. ………………………………………………………………………………………… (ii) Using the data from the graph, calculate the ΔHreaction. (iii) Suggest a simple practical change to the method that will make the experiment more accurate. …………………………………………………………………………………………. …………………………………………………………………………………………. [5] Total 12 marks 70.0 60.0 50.0 40.0 30.0 20.0 10.0 0.0 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 Mass of zinc / g DT/ oC

5 SRJC PRELIM 9647 P2 Turn Over] 2 (a) Pyruvic acid is an important component in living cells as it is involved in the aerobic process of supplying energy. The flow chart shows a series of reactions starting with compound A, which has an empirical formula of CH2. CH3CCOOH O For Examiner’s Use (i) Draw the structures of compounds A, B and C in the boxes above. (ii) State the reagents and conditions for steps I and II. Step I: …………………………………………………. Step II: ………………………………………………… [5] Cr2O72- / H+ distilation Ethanal I HCN, NaCN, cold H+, heat Ethanedioic acid II A B C Pyruvic acid H2O / H+

6 SRJC PRELIM 9647 P2 Turn Over] (b) Element D can form two different chlorides. The two chlorides of element D is commonly used in Organic Chemistry qualitative analysis to test for a specific functional group. When dissolved in a solution containing methyl orange, chlorides of element D turn the solution red. 10 cm 3 of li quid organic compound E, CnH2n+2O, is vaporised and burnt in excess oxygen. After the reaction is cooled to 25 oC, a contraction of 20 cm 3 in the gas volume was observed. When the result ant gases from the combustion were passed through aqueous sodium hydroxide, the gas volume decreased a further 20 cm 3. The v apour of E is also observed to react with the same reagents and conditions of step II mentioned in (a). For Examiner’s Use (i) State the identities of element D and organic compound E. D: ………………………….. E: …………………………. (ii) Hence write an equation, if any, between one of the chlorides of element D and organic compound E. ………………………………………………………………………………… ………. [3] Total 8 marks

7 SRJC PRELIM 9647 P2 Turn Over] 3 (a) (i) Both strontium and manganese are silvery metal s. Complete the electronic configurations of manganese and strontium below. For Examiner’s Use Mn: [Ar] …………………… S