Paper_3_Question_Paper

RAFFLES INSTITUTION 2021 YEAR 6 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS INDEX NUMBER CHEMISTRY 9729/03 Paper 3 Free Response 17 September 2021 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Do not open this question booklet until you are told to do so. Write your name, class and index number in the spaces provided at the top of this page. 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. Answer all questions in the spaces provided on the Question Paper. If additional space is required, you should use the pages at the end of this booklet. The question number must be clearly shown. 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. Do not write anything in it. You are reminded of the need for good English and clear presentation in your answers. 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 Section A Section B Total 1 / 23 (Circle the question you have answered) / 80 2 / 20 4 / 20 3 / 17 5 / 20 This document consists of 32 printed pages and 4 blank pages.

2 © Raffles Institution 2021 9729/03/S/21 [Turn Over Section A Answer all the questions in this section. 1 Alcohols, carbonyl compounds and esters are commonly found in both natural and artificial flavourings. (a) (i) When iodine dissolves in hexane, the solution is purple. Describe a reaction that uses this observation to illustrate the relative oxidising abilities of iodine and chlorine. [1] (ii) Explain the above reaction using relevant E ⦵ values from the Data Booklet. [1] (iii) Ascorbic acid (Mr = 176.0) is a food additive commonly added to candy to give a sour flavour. Iodine can be used to determine the amount of ascorbic acid in food by oxidising the ascorbic acid to dehydroascorbic acid. O HO OH OHO OH O O O OHO OH + 2H+ + 2e- ascorbic acid dehydroascorbic acid A 100.0 g sample of a candy was dissolved in hot water. The resulting solution was filtered and diluted to 100 cm3 in a volumetric flask. A 10.0 cm3 aliquot of the solution was pipetted into a conical flask and a few drops of starch solution was added. The sample was then titrated with 0.005 mol dm–3 of iodine solution. The titre volume was 22.05 cm3. Calculate the percentage by mass of ascorbic acid in the candy. [3] …………………………………………………………………………………….. …………………………………………………………………………………….. …………………………………………………………………………………….. …………………………………………………………………………………….. …………………………………………………………………………………