2023 ACJC H2 Chem Prelim P4 Solutions

© ACJC 2023 9729/04/Prelim/2023 [Turn over Anglo-Chinese Junior College JC2 Preliminary Examination Higher 2 CANDIDATE NAME SUGGESTED SOLUTIONS FORM CLASS TUTORIAL CLASS INDEX NUMBER CHEMISTRY Paper 4 Practical Candidates answer on the Question Paper. 9729/04 1 August 2023 2 hours 30 minutes READ THESE INSTRUCTIONS FIRST Write your index number and name 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 21 and 22. 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 / 16 2 / 19 3 / 20 Total / 55 This document consists of 20 printed pages and 2 blank pages. Shift Laboratory

© ACJC 2023 9729/04/Prelim/2023 [Turn over 2 1 Determination of the change in the oxidation number of a transition metal ion, X2+ FA 1 is 0.0125 mol dm−3 potassium manganate(VII), KMnO4 FA 2 is 0.0720 mol dm−3 transition metal salt, XSO4 FA 3 is 1.00 mol dm−3 sulfuric acid, H2SO4 You are to determine, by titration, the change in the oxidation number of a transition metal ion, X2+, upon oxidation by acidified potassium manganate(VII). (a) Procedure 1. Fill the burette with FA 1. 2. Using the pipette, transfer 25.0 cm3 of FA 2 into the conical flask. 3. Using a measuring cylinder, transfer 10.0 cm3 of FA 3 to the same conical flask. 4. Titrate the mixture in the conical flask with FA 1. The end-point is reached when the first permanent pale pink colour is seen. 5. Record your titration results, to an appropriate level of precision, in the space provided. 6. Repeat steps 2 to 5 to obtain consistent results. (i) Titration results Final burette reading / cm3 27.90 27.90 Initial burette reading / cm3 0.00 0.00 Volume of FA1 used / cm3 27.90 27.90 [2] (ii) From your titration results in (a)(i), obtain a suitable volume of FA 1, VFA 1, to be used in your calculations. Show clearly how you obtained this volume. Average titre volume = (27.90 + 27.90) / 2 = 27.90 cm3 VFA 1 = ....................................... [4]

© ACJC 2023 9729/04/Prelim/2023 [Turn over 3 (b) (i) Calculate the amount of MnO4– present in VFA 1 obtained in (a)(ii). Amount of MnO4– = 27.90/1000 x 0.0125 = 3.488 x 10–4 = 3.49 x 10–4 mol (3 s.f.) amount of MnO4– =