TJC 2024 JC2 Prelims H2 Paper 4 Solutions

9729 / TJC Prelim / 2024 [Turn Over TEMASEK JUNIOR COLLEGE 2024 JC2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME MARK SCHEME CLASS CENTRE NUMBER S INDEX NUMBER Chemistry 9729/04 Paper 4 Practical 26 August 2024 2 hours 30 minutes Candidates answer on the Question Paper. READ THESE INSTRUCTIONS FIRST Write your name, CG, centre number and index number 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 19 and 20. 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. This document consists of 18 printed pages and 2 blank pages. For Examiner’s Use 1 / 16 2 / 13 3 / 16 4 / 10 Total / 55 Shift Laboratory

2 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelim / 2024 Answer all the questions in the spaces provided. 1 Determination of the formula of hydrated sodium thiosulfate. In this experiment, you will determine the value of x in the formula of hydrated sodium thiosulfate, Na2S2O3xH2O, where x is an integer. You will first react IO3– ions with an excess of iodide ions, I–, to form iodine, I2. The amount of iodine produced will then be determined by titration with thiosulfate ions, S2O32–. I2 + 2S2O32– → 2I– + S4O62– FA 1 is 27.3 g dm-3 of hydrated sodium thiosulfate, Na2S2O3xH2O. FA 2 is 0.0150 mol dm-3 potassium iodate(V), KIO3. FA 3 is 0.500 mol dm-3 potassium iodide, KI. FA 4 is 2.20 mol dm-3 hydrochloric acid, HCl. Starch indicator (a)(i) Procedure 1. Fill the burette with FA 1. 2. Pipette 25.0 cm3 of FA 2 into a conical flask. 3. Use a measuring cylinder to add 10 cm3 of FA 3 to the conical flask. 4. Use another measuring cylinder to add 20 cm3 of FA 4 to the conical flask. The solution will turn brown. 5. Add FA 1 from the burette until the solution in the conical flask turns pale yellow. 6. Add 10 drops of starch indicator to the conical flask. The solution will turn blue-black. 7. Continue to add more FA 1 from the burette until the blue-black colour just disappears. This is the end point of the titration. 8. Repeat steps 2 to 7 until consistent results are obtained. Keep FA 4 for use in Question 2. Keep FA 1 and FA 3 for use in Question 3. Titration results Final burette reading/ cm3 20.50 4