2023 RI H2 Chem Prelims P4 Questions

© Raffles Institution 2023 9729/04/A/23 [Turn Over CANDIDATE NAME ( ) CLASS 23S0 RAFFLES INSTITUTION 2023 YEAR 6 PRELIMINARY EXAMINATION Higher 2 CHEMISTRY Paper 4 Practical 9729/04 23 August 2023 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 a 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 number of marks is given in brackets [ ] at the end of each question or part question. 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 23 and 24. Shift Laboratory Bench Number For Examiner’s Use Question Marks 1 / 14 2 / 13 3 / 17 4 / 11 Total / 55 This document consists of 21 printed pages and 3 blank pages.

2 © Raffles Institution 2023 9729/04/A/23 [Turn Over Answer all the questions in the spaces provided. 1 Determination of the kinetics of the reaction between iron(III) and iodide ions Iron(III) ions, Fe3+, oxidise iodide ions, I−, to iodine, I2. equation 1 2Fe3+(aq) + 2I−(aq) ⎯→ 2Fe2+(aq) + I2(aq) The rate of this reaction can be measured by adding thiosulfate ions, S2O32−, and some starch indicator to the mixture. As the iodine is produced, it reacts immediately with the thiosulfate ions and is reduced back to iodide ions. equation 2 I2(aq) + 2S2O32−(aq) ⎯→ 2I−(aq) + S4O62−(aq) When all the thiosulfate ions have reacted, the iodine which continues to be produced in equation 1 then turns the starch indicator blue-black. The rate of reaction may be determined by measuring the time taken for the reaction mixture to turn blue-black. FA 1 is aqueous iron(III) chloride, FeCl3. FA 2 is 0.0500 mol dm−3 aqueous potassium iodide, KI. FA 3 is 0.00500 mol dm−3 sodium thiosulfate, Na2S2O3. You will perform a series of four experiments. You will add a fixed amount of sodium thiosulfate, FA 3, to ea