CJC Prelim P3_QN

[Turn over 9729/03/CJC JC2 Preliminary Examination 2017 CHEMISTRY 9729/03 Paper 3 Free Response 25 August 2017 2 hours Candidates answer on separate paper. Additional Materials: Answer Paper 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. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Section A Answer all questions. Section B Answer one question. 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. This document consists of 14 printed pages and 0 blank page. Instruction Catholic Junior College JC2 Preliminary Examinations Higher 2

2 9729/03/CJC JC2 Preliminary Examination 2017 Section A Answer all the questions in this section. 1 Use of the Data Booklet is relevant to this question. (a) Under acidic conditions, ethanol reacts with dichromate( VI) ions quantitatively to give ethanoic acid and chromium(III) ions. 3CH3CH2OH + 2Cr2O72– + 16H+  3CH3CO2H + 4Cr3+ + 11H2O A student carried out th e following experiment to determine the concentration of ethanol in a brand of wine. A 10.0 cm 3 sample of the wine was diluted to 250 cm 3. He then added 25.0 cm 3 of 0.156 mol dm–3 K2Cr2O7(aq) and excess dilute H2SO4 to a 25.0 cm3 portion of the diluted solution. After allowing the mixture to stand for about an hour at room temperature, the excess K2Cr2O7 in the mixture was then titrated with 0.118 mol dm –3 (NH4)2Fe(SO4)2(aq) using an appropriate indicator. At the end-point of the titration, he used 12.25 cm3 of the Fe2+(aq) solution. (i) Write an ionic equation for the reaction that occurs during titration. [1] (ii) Calculate the concentration, in mol dm–3, of ethanol in this brand of wine. [4] (b) The relatively high alcohol content in wine makes it difficult to pair wine with spicy food because the combination can create a painful burning sensation on the lips and tongue that cannot be wiped or rinsed away. Capsaicin, C 18H27NO3, is the active ingredient in spicy food that gives the h ot taste of chilli peppers. The structure of capsaicin can be deduced from the following reactions. When capsaicin is boiled with dilute sulfuric acid , compound A, C10H18O2, and the salt of compound B, are produced. Compound B, C8H11NO2, has the structure shown, where the CH3O– group can be regarded as inert. compound B When A is heated with concentrated acidified KMnO 4, compound C, C 6H10O4, and compound D, C 4H8O2, are produced. C can be prepared from Br(CH 2)4Br in two steps whereas D can be prepared directly from (CH3)2CHCH2OH. Compounds A, C and D all react with aqueous so