TMJC 2022 H2 Chem Prelim P4 (QP)

CANDIDATE NAME CIVICS GROUP 21S H2 CHEMISTRY 9729 / 04 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 21 and 22. 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 Exam 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 the 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 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 filter 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 Exam H2 Chemistry [Turn Over (i) Results [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. 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 = [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 = [1] M8

4 Tampines Meridian Junior College 2022 JC2 Preliminary Exam H2 Chemistry (iii) Use your answer from (c)(ii) to calculate the Mrof the hydrated iron( III) sulfate, Fe2(SO4)3.nH2O, in FA 1. Mr of the hydrated iron(III) sulfate = Hence, deduce the value of n, the water of crystallisation in the hydrated iron(III) sulfate. [Ar: Fe, 55.8; S, 32.1; O, 16.0; H, 1.0] n = [2] M9 M10 (d) In step 4, excess zinc was filtered off before titration of FA 4 against FA 3. Suggest why it was necessary to filter off the excess zinc metal, and what effect it would have on the titre values if this filtration was not carried out. [1] M11 [Total: 11]

5 Tampines Meridian Junior College 2022 JC2 Preliminary Exam H2 Chemistry [Turn Over 2 Determination of the kinetics of the reaction between M3+ ions and iodide ions, I−. You are provided with the following reagents. FA 5 contains 0.0200 mol dm–3 metal ions, M3+, also present in FA 9. FA 6 is 0.0080 mol dm−3 aqueous potassium iodide, KI FA 7 is 0.0060 mol dm−3 sodium thiosulfate, Na2S2O3 starch solution M3+ ions oxidise iodide ions, I–, to iodine, I2 as shown in equation 1. In this experiment, you will investigate how the rate of this reaction is affected by the concentration of M3+ ions. equation 1 2M3+(aq) + 2I−(aq) → 2M2+(aq) + I2(aq) A fixed and small amount of thiosulfate ions, S 2O32–, and starch indicator will be added to a mixture of M3+(aq) and I–(aq). The iodine, I2, produced reacts immediately with thiosulfate ions, S 2O32− as shown in equation 2. equation 2 I2(aq) + 2S2O32−(aq) → 2I−(aq) + S4O62−(aq) When all the thiosulfate has been used, the iodine produced will turn starch indicator blue -black. The rate of the reaction can therefore be measured by finding the time it takes for the reaction mixture to turn blue–black. You will perform a series of four experiments. Then, you will graphically analyse your results to determine the order with respect to the concentration of M3+ ions, [M3+]. For each experiment, you will note the volume of FA 5 added, VFA 5, and the time taken, t, for the reaction mixture to become blue -black. In each experiment, you will need to ensure that the same total volume of reaction mixture is used by adding deionised water as required. You will then calculate values for • 1 t , • Ig 1 t   , • Ig(VFA 5). (a) Prepare a table in the space provided on page 7 in which to record, to an appropriate level of precision: • volumes of FA 5 and deionised water, • all values of t, • all calculated values of 1 t , Ig 1 t   and Ig(VFA 5).

6 Tampines Meridian Junior College 2022 JC2 Preliminary Exam H2 Chemistry (i) Experiment 1 1. Fill a burette with FA 5. 2. Transfer 20.00 cm3 of FA 5 into a 100 cm3 conical flask. 3. Use the measuring cylinders to place the following in a 100 cm3 beaker. • 10 cm3 of FA 6 • 15 cm3 of FA 7 • 10 cm3 of starch solution 4. Add the contents of the beaker rapidly to the conical flask and start the stopwatch. 5. Swirl the mixture and place the conical flask on the white tile. 6. The mixture turns purple and then yellow before turning a blue -black colour. Stop timing when this blue-black colour first appears. 7. Record the time taken, t, to nearest second in your table. 8. Discard the reaction mixture immediately down the sink. Wash out the conical flask and stand it upside down on a paper towel to drain. (ii) Experiment 2 1. Run 8.00 cm3 of FA 5 into a 100 cm3 conical flask. 2. Using another measuring cylinder, add 12.0 cm3 of deionised water into the conical flask containing FA5. 3. Use the measuring cylinders from Experiment 1 to place the following in a 100 cm3 beaker. • 10 cm3 of FA 6 • 15 cm3 of FA 7 • 10 cm3 of