2025 H2 Chem Prelim Paper 4 (QP) _ ACJC

Anglo-Chinese Junior College JC2 Preliminary Examination Higher 2 CANDIDATE NAME FORM CLASS TUTORIAL CLASS INDEX NUMBER CHEMISTRY Paper 4 Practical Candidates answer on the Question Paper. 9729/04 5 August 2025 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 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. For Examiner’s Use 1 / 17 2 / 21 3 / 17 Total / 55 This document consists of 18 printed pages and 1 blank page. Shift Laboratory

© ACJC 2025 9729/04/Prelim/2025 2 1 Determination of the stoichiometry of the reaction between hydroxylamine and iron(III) ion A redox reaction takes place between hydroxylamine, NH 2OH, and iron(III) ion, Fe 3+, in an acidic medium. The iron(III) ion is converted to iron(II) ion, Fe2+. The reaction is slow at room temperature, but is completed in a few minutes when heated to 90 oC. The iron(II) ions formed can then be oxidised by manganate(VII) ions for quantitative analysis. You are to determine, by titration, which of the following unbalanced equations represents the reaction between hydroxylamine and iron(III) ion. equation 1.1 NH2OH + Fe3+ → Fe2+ + …N2 + …H+ + …H2O equation 1.2 NH2OH + 2Fe3+ → 2Fe2+ + …N2O + …H+ + …H2O equation 1.3 NH2OH + 3Fe3+ → 3Fe2+ + …NO + …H+ FA 1 is 0.0150 mol dm−3 potassium manganate(VII), KMnO4. FA 2 is a solution prepared by boiling a 1.00 dm3 aqueous mixture of 3.30 g of hydroxylamine hydrochloride, NH2OH.HCl, excess iron(III) chloride, FeCl3, and excess sulfuric acid, H2SO4. FA 3 is 1.00 mol dm−3 sulfuric acid, H2SO4. (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 [2]

© ACJC 2025 9729/04/Prelim/2025 [Turn over 3 (ii) From