RI Prelim P4_QP

© Raffles Institution 2018 9729/04/A/18 [Turn Over CANDIDATE NAME ( ) CLASS 18S0 RAFFLES INSTITUTION 2018 YEAR 6 PRELIMINARY EXAMINATION Higher 2 CHEMISTRY Paper 4 Practical 9729/04 29 August 2018 2 hours 30 minutes Do NOT turn over the Question Booklet until you are told to do so. READ THESE INSTRUCTIONS FIRST Write your name and class on the space provided when instructed to do so. Give details of the practical shift and laboratory, where appropriate, in the space provided. 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. The use of an approved scientific calculator is expected, where appropriate. You may lose marks if you do not show your working or if you do not use appropriate units. Qualitative Analysis Notes are printed on pages 17 and 18. 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. Shift Laboratory Bench Number For Examiner’s Use Question Marks 1 / 14 2 / 25 3 / 16 Total / 55 This document consists of 17 printed pages and 1 blank page.

- 2 - © Raffles Institution 2018 9729/04/A/18 [Turn Over Answer all the questions in the spaces provided. 1 Determination of the concentration of CuSO 4 in FA 2 You are provided with the following solutions: FA 1 0.0500 mol dm–3 aqueous sodium thiosulfate, Na2S2O3 FA 2 aqueous CuSO 4 solution of unknown concentration FA 3 100 g dm−3 solution of sodium iodide, NaI Starch solution Copper(II) ions react with iodide ions according to the following equation. 2Cu2+(aq) + 4I⁻(aq) ⎯→ 2CuI(s) + I2(aq) The iodine produced in this reaction may be titrated against FA 1 using starch solution as indicator. Thiosulfate ions react with iodine according to the following equation: 2S2O32–(aq) + I2(aq) ⎯→ S4O62–(aq) + 2I–(aq) Estimating the required dilution factor for FA 2 (a) The solution of FA 2 provided is too concentrated to be used directly for reaction with FA 3 to produce iodine for titration against FA 1. A preliminary experiment was carried out to estimate a dilution factor for the FA 2 solution, so that 25 cm 3 of this diluted solution would require approximately 25 cm 3 of FA 1 for complete reaction. It was found that 30 drops of FA 1 were needed to react completely with the iodine produced from the reaction between 5 drops of FA 2 and excess FA 3. Use