TMJC 2022 H2 Chem Prelim P4 (Ans)

1 Tampines Meridian Junior College 2022 JC2 Preliminary Examination H2 Chemistry [Turn Over CANDIDATE NAME SUGGESTED SOLUTIONS CIVICS GROUP 21S H2 CHEMISTRY 9729 Paper 4 Practical 30 August 2022 2 hours 30 minutes Candidates answer on the Question Paper. This document consists of 22 printed pages. READ THESE INSTRUCTIONS FIRST Write your name and Civics Group in the spaces at the top of the 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 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. The number of marks is given in brackets [ ] at the end of each question or part question. Shift 1 / 2 / 3 Laboratory For Examiner’s Use 1 / 11 2 / 20 3 / 10 4 / 14 Total / 55 TAMPINES MERIDIAN JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION

2 Tampines Meridian Junior College 2022 JC2 Preliminary Examinations H2 Chemistry 1 Determination of water of crystallisation in a hydrated iron(III) salt A variety of hydrated iron(III) sulfates are known. Solutions of iron(III) sulfate are used in dyeing, and as coagulant for industrial waste. FA 1 is a solution containing 26.0 g dm–3 of hydrated iron(III) sulfate, Fe2(SO4)3.nH2O. The addition of excess zinc to a solution of FA 1 reduces the Fe3+ ions to Fe2+ ions. The amount of Fe2+ ions can be determined quantitatively by titration against a standard solution of potassium manganate(VII), KMnO4. The reaction is shown below. 5Fe2+ + MnO4− + 8H+ → 5Fe3+ + Mn2+ + 4H2O In this experiment, you are to perform titrations to determine th e value of n, the water of crystallisation in FA 1. You are provided with FA 1, solution containing 26.0 g dm–3 of hydrated iron(III) sulfate, Fe2(SO4)3.nH2O. FA 2, dilute sulfuric acid, FA 3, 0.0200 mol dm−3 potassium manganate(VII), KMnO4, zinc powder . (a) Preparation of Fe2+ solution from FA 1 1. Use a measuring cylinder to transfer 80 cm3 of FA 1 into a 250 cm3 beaker. 2. Add cautiously all the zinc powder into the beaker. Cover the beaker with a white tile. 3. Allow the reaction to take place for about 5 minutes, stirring the reaction mixture from time to time. 4. Filter the mixture into the dry beaker provided using a dry filter paper and f ilter funnel. Ignore any reaction that may still be taking place. 5. Label the filtrate as FA 4. Proceed to 1(b) once you have collected sufficient filtrate. (b) Titration of FA 4 against FA 3 6. Fill the burette labelled FA 3 with FA 3. 7. Use a pipette to transfer 10.0 cm3 of FA 4 into a 100 cm3 conical flask. 8. Use a measuring cylinder to add 10 cm3 of FA 2 to this flask. 9. Titrate FA 4 with FA 3 from the burette until the appearance of the first permanent pale pink colour. 10. Record your titration results, to an appropriate level of precision, in the space provided on page 3. 11. Repeat steps 7 to 10 until consistent results are obtained. Wash out the conical flasks and stand it upside down to drain for use in Question 2.

3 Tampines Meridian Junior College 2022 JC2 Preliminary Examination H2 Chemistry [Turn Over (i) Results Final burette reading / cm3 9.90 19.80 Initial burette reading / cm3 0.00 9.90 Volume of FA 3 used / cm3 9.90 9.90   [3] (ii) From your titrations, obtain a suitable volume of FA 3 , VFA 3 , to be used in your calculations. Show clearly how you obtained this volume. Average volume of FA3 = (9.90 + 9.90)  2 = 9.90 cm3 VFA 3 = [3] M1 M2 M3 M4 M5 M6 (c) (i) Calculate the amount of Fe2+ in 10.0 cm3 of FA 4. amount of Fe2+ in 10.0 cm3 of FA 4 = mol [1] M7 (ii) In step 2, an excess of zinc was added to convert the Fe3+ to Fe2+. Calculate the amount of Fe3+ in 1 dm3 of FA 1. amount of Fe3+ in 1 dm3 of FA 1 = mol [1] M8 5Fe2+  MnO4− Amount of Fe2+ in 10.0 cm3 of FA 4 = 9.90 1000  0.0200  5 = 9.90  10–4 mol (3 s.f.) Amount of Fe3+ in 1 dm3 of FA 1 = 9.90  10–4  1000 10.0 = 9.90  10–2 mol (3 s.f.)

4 Tampines Meridian Junior College 2022 JC2 Preliminary Examinations H2 Chemistry (iii) Use your answer from (c)(ii) to calculate the Mr of the hydrated iron( III) sulfate, Fe2(SO4)3.nH2O, in