2021 MI Prelim H2 Chemistry P4 (9729_04) Answers

Class Adm No Candidate Name: This question paper consists of 19 printed pages and 1 blank page. 2021 Preliminary Examinations Pre-University 3 H2 CHEMISTRY 9729/04 Paper 4 Practical 1 Sept 2021 2 hours 30 min 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 4 Total Marks 13 20 10 12 55 Shift Laboratory

2 1 Determine the formula of the ion IOx– by titration In this experiment you will determine the formula of the ion, IOx–. Iodine, I2, is formed when IOx– ions reacts with an excess of iodide ions. The equation for this reaction is: IOx– + y I– + z H+ → (y+12) I2 + z2 H2O where x, y and z are all integers. The amount of iodine produced will then be determined by titration with thiosulfate ions, S2O32–. I2 + 2S2O32– → 2I– + S4O62– FA 1 is a solution containing 0.0150 mol dm–3 IOx– ions. FA 2 is dilute sulfuric acid, H2SO4. FA 3 is 0.500 mol dm–3 potassium iodide, KI. FA 4 is 0.100 mol dm–3 sodium thiosulfate, Na2S2O3. starch indicator (a) Method • Pipette 25.0 cm3 of FA 1 into a conical flask. • Using a measuring cylinder, add 20.0 cm3 of FA 2 to the conical flask. • Using a measuring cylinder, add 10.0 cm3 of FA 3 to the conical flask. The solution will turn brown as iodine is produced. • Fill the burette with FA 4. • Add FA 4 from the burette until the solution in the conical flask turns yellow. • Add 1 cm3 of starch indicator to the conical flask. The solution will turn blue-black. • Continue to add more FA 4 dropwise from the burette until the blue-black colour just disappears. This is the end-point of the titration. • Carry out as many accurate titrations as you think necessary to obtain consistent results. • Record the burette readings and the volume of FA 4 added in each accurate titration in the space below. Results Initial burette reading / cm3 0.00 0.00 Final burette reading / cm3 22.50 22.50 Volume of FA 4 added / cm3 22.50 22.50 ✓ ✓ M1 table w headers and units M2 readings to 0.05 cm3 + correct calc M3 2 consistent values within 0.10 M4 accuracy M5 accuracy

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