2019 CJC Prelim H2 Chem P4 ANS

CANDIDATE NAME CLASS 2T CHEMISTRY 9729/04 Paper 4 Practical 19 August 2019 2 hours 30 minutes Candidates answer on the Question Paper. Additional Materials: As listed in the Confidential Instructions READ THESE INSTRUCTIONS FIRST Write your name and class in the boxes above. 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 14 and 15. 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 15 printed pages and 1 blank page. [Turn over Instruction Catholic Junior College JC2 Preliminary Examinations Higher 2 Shift Laboratory For Examiner’s Use 1 16 2 14 3 13 4 12 Total 55

2 9729/04/CJC JC2 Preliminary Examination 2019 1 Determination of the percentage by mass of iron(II) sulfate in an iron tablet Iron tablets, taken for the prevention and treatment of iron deficiency, are health supplements readily available in pharmac ies. These iron tablets contain iron(II) sulfate, which is a soluble form of iron. Assuming that all the iron in the tablets is in the form of Fe2+, it is possible to estimate the iron content by titration against potassium manganate(VII). The equation for this reaction is 5Fe2+(aq) + MnO4–(aq) + 8H+(aq)  5Fe3+(aq) + Mn2+(aq) + 4H2O(l) You are provided with the following. FA 1 contains 5 iron tablets, crushed to a powder. FA 2 is 0.00500 mol dm–3 potassium manganate(VII), KMnO4. 1.0 mol dm–3 sulfuric acid, H2SO4. deionised water In this experiment, you will determine the percentage of iron(II) sulfate heptahydrate, FeSO4.7H2O, present in the iron tablets FA 1. (a) Preparation of FA 3, a solution of FeSO4.7H2O.  Use a measuring cylinder to transfer about 100 cm3 of 1.0 mol dm–3 sulfuric acid into a conical flask.  Determine accurately the mass of the crushed iron tablets used, FA 1, and record your readings in the space below. mass of the crushed iron tablets used = ……………. g  Add all the crushed tablets, FA 1, to the sulfuric acid.  Warm the mixture gently, do not overheat, and stir for about two minutes.  Allow the flask to cool for around five minutes.  Filter the mixture into a 250 cm3 volumetric flask. Ensure that no solution is lost. Note: Th e filtration takes time . Proceed to Question 2 whilst the mixture is filtering.  Wash out the conical flask with deionised water a