2023_NJC_H2_Chemistry_Prelim_Paper 4_Ans

1 NJC SH2 Preliminary Examination 9729/04/23 [Turn over NATIONAL JUNIOR COLLEGE SH 2 Year − End Practical Examination Higher 2 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER CHEMISTRY Paper 4 Practical Candidates answer on the Question paper. 9729/04 Tuesday 15 August 2023 2 hours 30 minutes READ THESE INSTRUCTIONS FIRST Write your identification number and name. Give details of the practical shift and laboratory where appropriate, in the boxes provided. Write in 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. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 20 printed pages and 0 blank page. Shift Laboratory For Examiner’s use 1 / 13 2 / 17 3 / 13 4 / 12 Total / 55

2 NJC SH2 Preliminary Examination 9729/04/23 1 Determine the reacting mole ratio of reagent X with Fe2+ Iron(II) ions, Fe2+, is readily oxidized. Fe2+ → Fe3+ + e– A common oxidising agent for Fe2+ ion is manganate(VII) ions in an acidic medium. MnO4 – + 8H+ + 5e–  Mn2+ + 4H2O Another oxidising agent that is also able to oxidise Fe2+ to Fe3+ .is reagent X. In this experiment, a limited amount of X is added to a solution of Fe2+. The resultant mixture containing unreacted Fe(II) ions will be titrated with acidified MnO4 –. FA 1 is a solution containing 0.075 mol dm–3 iron(II) sulfate, FeSO4. FA 2 is 0.010 mol dm–3 potassium manganate(VII), KMnO4. FA 3 is 0.025 mol dm–3 of a reagent X. FA 4 is 1.0 mol dm–3 sulfuric acid, H2SO4. (a) Procedure 1. Fill a burette with FA 3 and another burette with FA 2. 2. Pipette 25.0 cm 3 of FA 1 into a conical flask and add 10 cm 3 of FA 4 using a 10.0 cm 3 measuring cylinder into the same conical flask. 3. Run 12.00 cm 3 of FA 3 from the burette into the conical flask. 4. Titrate the mixture against FA 2 until the first permanent pink colour remains in the solution. You only need to do the titration ONCE. Record your titration results in the space below. Final burette reading / cm3 Initial burette reading / cm3 Volume of FA 2 added / cm3 24.50 (shift 1) 24.20 (shift 2) 24.00 (shift 3) Tables with correct headings and units(Do no award if did not put “burette”) (Do not award if any final and initial burette readin