2022 TJC Prelims H2 Paper 4 QP

9729 / TJC Prelims / 2022 DO NOT WRITE IN THIS MARGIN [Turn over TEMASEK JUNIOR COLLEGE 2022 JC2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CIVICS GROUP / CENTRE NUMBER S INDEX NUMBER Chemistry 9729/04 Paper 4 Practical 29 August 2022 2 hours 30 minutes Candidates answer on the Question Paper. READ THESE INSTRUCTIONS FIRST Write your Civics Group and name on all the work you hand in. 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 23 and 24. 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 23 printed pages and 1 blank page. For Examiner’s Use 1 / 12 2 / 19 3 / 14 4 / 10 Total / 55 Shift Laboratory

2 DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2022 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN Answer all the questions in the spaces provided. 1 Determination of the percentage by mass of water of crystallisation in FeSO4·nH2O Read through the whole method before starting any practical work. Where appropriate, prepare a table for your results in the space provided. Show your working and appropriate significant figures in the final answer to each step of your calculations. The amount of Fe 2+ ions can be determined quantitatively by a 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 will determine the percentage by mass of water of crystallisation in FeSO4·nH2O. You will titrate a solution of FA 1 against FA 3. You are provided with FA 1, contains 26.07 g dm–3 of hydrated iron(II) sulfate, FeSO4•nH2O, where n is an integer. FA 2, 1.0 mol dm-3 dilute sulfuric acid, H2SO4 FA 3, 0.0200 mol dm−3 potassium manganate(VII), KMnO4 You are to keep FA 2 and FA 3 for questions 2 and 3. (a) (i) Titration of FA 1 against FA 3 1. Fill a burette, labelled FA 3, with FA 3. 2. Use a pipette to transfer 10.0 cm3 of FA 1 into a 250 cm3 conical flask. 3. Use a measuring cylinder to add about 10 cm3 of FA 2 to this flask. 4. Titrate FA 1 with FA 3 from the burette until the appearance of the first permanent pale-pink colour. 5. Record your titration results, to an appropriate level of precision, in the space on Page 3. 6. Repeat steps 1 to 4 until consistent results are obtained.

3 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2022 DO NOT WRITE IN THIS MARGIN [Turn over Titration Results [2] (ii) From your titrations, obtain a suitable volume of FA 3 to be used in your calculations. Show clearly how you obtained this volume. volume of FA 3 = ………………………………………………[3] (b) (i) Calculate the amount of Fe2+ in 10.0 cm3 of FA 1. amount of Fe2+ in 10.0 cm3 of FA 1 = …………………. [1]

4 DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2022 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN (ii) Calculate the amount of Fe2+ in 1 dm3 of FA 1. amount of Fe2+ in 1 dm3 of FA 1 = …………………. [1] (iii) Calculate the Mr of the hydrated iron(II) sulfate, FeSO4.nH2O, in FA 1. Mr of the hydrated iron(II) sulfate = …………………………………. Hence, deduce the value of n, the water of crystallisation in the hydrated iron( II) sulfate. [Ar: Fe, 55.8; S, 32.1; O, 16.0; H, 1.0] n = ……………………………….. [2]

5 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2022 DO NOT WRITE IN THIS MARGIN [Turn over (iv) Hence, determine the percentage by mass of water of crystallisation in FeSO4·nH2O. Show your working. Percentage by mass of water of crystallisation = ……………………………….. [1] (v) Iron(II) sulfate in solution is readily oxidised by air to form iron(III) sulfate. State the effect, on the value of n calculated in (b)(iii), if some of your sample of FA 1 had oxidised before you carried out the titration. Explain your answer. ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… …………………………………………………………………………………………….... [2] [Total: 12]

6 DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2022 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 2 To investigate the reaction between manganate(VII) ions and C2O42− ions In this experiment, you will investigate the kinetics of the reaction between MnO4– and C2O42–. FA 4 is 0.0100 mol dm–3 sodium thiosulfate, Na2S2O3 FA 5 is 0.200 mol dm-3 sodium ethanedioate, Na2C2O4 FA 6 is 0.100 mol dm–3 potassium iodide, KI FA 2 and FA 3 are solutions from question 1. You are to keep FA 5 for question 3. You are also provided with a starch indicator. Acidified potassium manganate(VII) ions oxidises C 2O42− ions to produce Mn 2+ ions which act as an autocatalyst for the reaction. 2 MnO4–(aq) + 5 C2O42−(aq) + 16 H+(aq) → 2Mn2+(aq) + 10CO2(g) + 8H2O(I) Acidified potassium manganate(VII) ions also oxidises I− ions according to the following reaction: 2MnO4–(aq) + 10I−(aq) + 16H+(aq) → 2Mn2+(aq) + 5I2(aq) + 8H2O(I) You will add a solution of acidified potassium manganate(VII) to a mixture containing FA 2 and FA 5. At timed intervals, you will draw 10 cm 3 aliquots of the reacti on mixture. The concentration of MnO 4– ions in each aliquot will be determined after adding the aliquot to an excess of I− solution and titrating the iodine produced against S2O32− solution. The reaction between iodine from the reaction mixture and S2O32− solution is given below. 2S2O32–(aq) + I2(aq) → 2I–(aq) + S4O62–(aq) Note: C2O42− does not react with I− in the reaction mixture.

7 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2022 DO NOT WRITE IN THIS MARGIN [Turn over Question 2 continues on the next page.

8 DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2022 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN Note: Read all instructions in the procedure before you start performing the experiment. Recording your results In an appropriate format in the space provided on page 9, draw a table to record your • transfer time (in minutes and seconds, to the nearest second) when half of the reaction mixture has emptied from the pipette, • the decimal time, td, in minutes, to 0.1 min, for example, if t = 3 min 20 s then td = 3 min + 20/60 = 3.3 min, • titration results for eac h of your aliquots. Make certain that your recorded results show the precision of your working. Procedure 1. Label each of the large test-tubes 1 to 6. Using a measuring cylinder, add approximately 10 cm3 of FA 6 to each of these test-tubes. 2. Using appropriate measuring cylinders, transfer 50.0 cm 3 of FA 5 , 5.0 cm 3 of FA 2 and 45