HCI Prelim P4_QP

This document consists of 18 printed pages. HWA CHONG INSTITUTION C2 Preliminary Examination Higher 2 NAME CT GROUP 17S CHEMISTRY Paper 4 Practical Candidates answer on the Question Paper 9729/04 24 August 2018 2 hours 30 minutes READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. 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 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 For Examiner’s Use 1 2 3 4 Deductions Total

2 © Hwa Chong Institution 2018 9729 / 04 / C2 Prelim 2018 Answer all the questions in the spaces provided. 1 To determine the concentration of potassium iodate(V) FA 1 is a solution containing potassium iodate(V), K IO3. FA 2 is 1.0 mol dm −3 sulfuric acid, H2SO4. FA 3 is 0.50 mol dm−3 potassium iodide, KI. FA 4 is approximately 0.1 mol dm−3 sodium thiosulfate, Na2S2O3. You are also provided with starch solution. You are to determine the concentration of potassium iodate(V) present in FA 1. In acidic conditions, potassium iodate(V) oxidises iodide ions to iodine. Titration of this iodine with a standard solution of sodium thiosulfate allows the concentration of potassium iodate(V) to be determined. IO 3− + 5I− + 6H+ → 3I2 + 3H2O reaction 1 I2 + 2S2O32− → 2I− + S4O62− reaction 2 The solution of FA 1 is too concentrated to titrate directly with the FA 4 solution. You will prepare a diluted solution of FA 1. You will then use FA 4 to determine the concentration of potassium iodate(V) in the diluted solution by titration, and hence determine the concentration of potassium iodate(V) in FA 1. (a) Dilution of FA 1 You will now follow the instructions given below to prepare a diluted solution of FA 1. 1. Using a burette, measure between 49.00 cm 3 and 49.50 cm 3 of FA 1 into the 250 cm 3 graduated flask. In the space below, record your burette readings and the volume of FA 1 added to the flask. Make certain that your recorded results show the precision of your working. 2. Make up the contents of the flask to the 250 cm 3 mark with deionised water. Place the stopper in the flask and mix the contents thoroughly. This solution is FA 5.

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