2020 SAJC H2 Prelim Paper 4 (QP)

1 [Turn Over NAME Class ST ANDREW’S JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION Chemistry (9729) Paper 4 Practical 17 August 2020 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 on all the work you hand in. Give details of the practical shift and laboratory 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 the 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. Shift Laboratory Qualitative Analysis Notes are printed on pages 21 and 22. The number of marks is given in the brackets [ ] at the end of each question or part question. For Examiners’ Use 1 2 3 4 Total This document consists of 22 printed pages.

2 1 Investigation of the concentration of potassium manganate(VII) Potassium manganate(VII) is a very useful oxidising agent. It oxidises iron( II) ions in acidic medium according to equation 1. MnO4 (aq) + 5Fe2+ (aq) + 8H+ (aq)  Mn2+ (aq) + 5Fe3+ (aq) + 4H2O (l) equation 1 In solution, ammonium iron (II) sulfate, (NH 4)2SO4FeSO46H2O, dissociates into iron (II), sulfate and ammonium ions according to equation 2. (NH4)2SO4FeSO46H2O (s)  2NH4+ (aq) + 2SO42 (aq) + Fe2+ (aq) + 6H2O (l) equation 2 You are provided with FA 1, ammonium iron(II) sulfate crystals, FA 2, potassium manganate(VII) solution, 1.0 mol dm3 sulfuric acid. (a) (i) Preparation of standard solution of FA 3 and titration of FA 3 against FA 2 In an appropriate format in the space provided on page 3, prepare tables in which to record results for your experiment in (a):  All weighings to an appropriate level of precision  All burette readings and the volume of FA 2 added 1. Weigh the capped bottle containing FA 1. 2. Dissolve this in about 50 cm3 of 1.0 mol dm-3 sulfuric acid in a 100 cm3 beaker. 3. Transfer the solution and washings into a 250 cm3 standard flask. Make up to the mark with deionised water and shake well to obtain a homogeneous solution, FA 3. 4. Reweigh the emptied bottle and its cap. 5. Fill a burette with FA 2. 6. Pipette 25.0 cm3 of FA 3 prepared into a conical flask. 7. Add about 10 cm3 of aqueous sulfuric acid into the conical flask. 8. Run FA 2 from the burette into the flask. The end -point is reached when the solutions changes from pale green to orange. 9. Repeat steps 6 to 8 until consistent titres are obtained.

3 [Turn Over Results [4] (ii) From your titrations, obtain a suitable volume of FA 2 to be used in your calculations. Show clearly how you obtained t