MI 2020 Prelim Paper 4

Class Adm No Candidate Name: This question paper consists of 21 printed pages and 1 blank page. 2020 Preliminary Examinations Pre-University 3 H2 CHEMISTRY 9729/04 Paper 4 Practical 31 Aug 2020 2 hour 30 mins Candidates answer on the Question paper. READ THESE INSTRUCTIONS FIRST Do not turn over this question paper until you are told to do so Write your name, class and admission number 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. 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 at the back of the Question Paper. 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. Question 1 2 3 Total Marks 27 13 15 55 Shift Laboratory

2 1 Determination of the order of reaction with respect to H2O2 Hydrogen peroxide, H2O2, reacts with iodide ions, I-(aq), to form iodine, I2(aq). H2O2(aq) + 2H+(aq) + 2I–(aq) 2H2O(l) + I2(aq) The rate of this reaction can be measured by adding acidified hydrogen peroxide, H 2O2, to a mixture of iodide ions, I-, thiosulfate ions, S 2O32-, and starch indicator. The iodine, I2, produced from the reaction between acidified H2O2 and I- can be reacted immediately with thiosulfate ions, S2O32–. I2(aq) + 2S2O32–(aq) 2I–(aq) + S4O62–(aq) When all the thiosulfate has reacted, the iodine produced will then turn the starch indicator blue- black. The rate of the reaction can therefore be measured by the time taken for the reaction mixture to turn blue-black colour. FA 1 is 0.180 mol dm-3 hydrogen peroxide, H2O2. FA 2 is 0.200 mol dm-3 aqueous potassium iodide, KI. FA 3 is 0.0100 mol dm–3 sodium thiosulfate, Na2S2O3. FA 4 is 0.500 mol dm-3 aqueous sulfuric acid, H2SO4. starch indicator For Examiners’ Use (a) Procedure Experiment 1 1. Fill a burette with FA 1. 2. Run 20.00 cm3 of FA 1 from the burette into a 100 cm3 beaker. 3. Using a suitable measuring cylinder, measure 10 cm3 of FA 4 and transfer into the same 100 cm3 beaker. 4. Using suitable measuring cylinders, transfer the following into another 100 cm3 beaker.  10 cm3 FA 2  20 cm3 FA 3  5 cm3 of starch indicator 5. Add the contents of the second beaker to the first beaker and start the stopwatch. 6. Place the beaker on a white tile and stir the mixture once using a glass rod. 7. Observe the solution and stop the stopwatch when the solution turns blue-black. 8. Record the time taken to