2023 DHS H2 Chem Prelim Paper 4_Suggested Solutions

© DHS 2023 9729/04 [Turn over Suggested Solutions DUNMAN HIGH SCHOOL Preliminary Examination Year 6 H2 CHEMISTRY Paper 4 Practical Candidates answer on the Question Paper. 9729/04 24 August 2023 2 hours 30 minutes READ THESE INSTRUCTIONS FIRST Write your centre number, index number, name and class at the top of this page. 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 sci entific 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 23 and 24. 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 16 2 13 3 15 4 11 Total 55

2 © DHS 2023 9729/04 Answer all questions in the spaces provided. 1 Determination of change in oxidation number in XO3– oxidant. FA 1 is 0.0265 mol dm–3 potassium manganate(VII), KMnO4(aq) FA 2 is 0.0750 mol dm–3 XO3– oxidant solution. X is the symbol of an element whose identity is not needed in this question. FA 3 is a solution containing 0.150 mol dm–3 iron(II) ions, Fe2+. FA 3 solution is prepared by dissolving an iron(II) salt in sulfuric acid. In the presence of acid, XO3– oxidises iron(II) to iron(III) while itself is reduced to X b+. In order to determine b, a sample of XO3– is added to a known amount of iron(II) in excess. The amount of remaining iron(II) ions can then be determined by titration against manganate(VII) ions as shown in equation 1. equation 1 MnO4–(aq) + 8H+(aq) + 5Fe2+(aq) → Mn2+(aq) + 5Fe3+(aq) + 4H2O(l) (a) Procedure 1. Pipette 25.0 cm3 of FA 3 into a conical flask. 2. Using another pipette, add exactly 10.0 cm3 of FA 2 to FA 3 in the conical flask. 3. Fill the burette with FA 1. 4. Titrate the mixture in the conical flask with FA 1 until the appearance of the first permanent pale orange or pale pink colour. 5. Repeat the titration as many times as you think necessary to obtain accurate results. 6. Record your results of titration in a suitable tabulated form below. Results 1 2 Final burette reading / cm3 17.00 34.00 Initial burette reading / cm3 0.00 17.00 Volume of FA 1 (KMnO4) / cm3 17.00 17.00 [2] (b) From your titrations, obtain a suitable volume of FA 1, VFA 1, to be used in your calculations. Show clearly how you have obtained this volume. VFA 1 = 17.00+17.00 2 = 17.00 cm3 (2dp) VFA 1 = ……………….. cm3 [3