YIJC 2024 Prelim P4 Solutions

1 ©YIJC [Turn over YISHUN INNOVA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION CANDIDATE NAME SUGGESTED ANSWERS CLASS H2 CHEMISTRY 9729/04 Paper 4 Practical Paper 20 August 2024 2 hours 30 minutes Candidates answer on question paper. READ THESE INSTRUCTIONS FIRST This document consists of 24 printed pages and 1 blank page. Write your name and class in the spaces at the top of this page. Give details of the practical shift and laboratory where appropriate, in the boxes 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 23 and 24. 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 1 2 3 4 Total Shift Laboratory

2 ©YIJC [Turn over Answer all the questions in the spaces provided. 1 Determination of the kinetics of a redox reaction Equation 1 represents the reaction between iron(III) ions and iodide ions. equation 1 2Fe3+(aq) + 2I−(aq) → 2Fe2+(aq) + I2(aq) When starch is added to the reaction mixture, a blue colour is immediately seen due to the formation of an iodine−starch complex. If a small amount of sodium thiosulfate, Na2S2O3, is also present in the reaction mixture, the formation of the blue colour is delayed. The Na2S2O3 reacts with I2 as shown in equation 2. equation 2 I2(aq) + 2S2O32−(aq) → S4O62−(aq) + 2I−(aq) FA 1 is iron(III) chloride, FeCl3. FA 2 is potassium iodide, KI. FA 3 is 0.0060 mol dm−3 sodium thiosulfate, Na2S2O3. Solution S is starch indicator. You will perform a series of five experiments. Then, you will graphically analyse your results to determine the order with respect to the concentration of Fe3+ ions, [Fe3+]. You will add a fixed amount of sodium thiosulfate, FA 3, to each of your experiments. In each experiment, you will need to ensure that the same total volume of reaction mixture is used by adding deionised water as required. The time taken for the blue colour to form allows the reaction rate to be determined. (a) Prepare a table in the space provided on page 4 in which to record, to an appropriate level of precision: • all volumes, except the volume of sodium thiosulfate, potassium iodide and starch, • all values of t.

3 ©YIJC [Turn over Experiment 1 The end-point of the reaction is the first appearance of