2019 ASRJC Prelim H2 Chem P4 QP

ASRJC JC2 PRELIMS 2019 9729/04/H2 [Turn over ANDERSON SERANGOON JUNIOR COLLEGE 2019 JC 2 PRELIMINARY EXAMINATIONS NAME:______________________________ ( ) CLASS: 19 /____ CHEMISTRY 9729/04 Paper 4 Practical 27 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, class and index number 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 a pencil for any diagrams, graphs or rough working. 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. Quantitative Analysis Notes are printed on pages 22 and 23. 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. Shift For Examiner’s Use 1 Laboratory 2 3 Total This document consists of 23 printed pages.

2 ASRJC JC2 PRELIMS 2019 9729/04/H2 Answer all the questions in the spaces provided. 1 To determine the order of reaction with respect to the concentration of iodine in the iodination of propanone reaction FA 1 is 1.00 mol dm–3 propanone, CH3COCH3 FA 2 is 1.00 mol dm–3 sulfuric acid, H2SO4 FA 3 is an aqueous solution of iodine, I2 FA 4 is 0.0100 mol dm–3 sodium thiosulfate, Na2S2O3 FA 5 is 0.50 mol dm–3 sodium hydrogencarbonate, NaHCO3 You are also provided with a starch indicator. The iodination of propanone, to form iodopropanone, proceeds as shown in the equation below. Reaction 1: CH3COCH3(aq) + I2(aq) → CH3COCH2I(aq) + HI(aq) This reaction is first order with respect to both CH3COCH3 and H+ ions. You are to investigate the order of reaction with respect to I2. A reaction mixture containing FA 1, FA 2, and FA 3 is first prepared . At different chosen times, aliquots (fixed volumes) of this reaction mixture is removed and quenched using excess FA 5. The remaining amount of I2 at different times can then be determined by titration against FA 4. Each titration can only be performed once. Reaction 2: 2S2O32–(aq) + I2(aq) → 2I–(aq) + S4O62–(aq) The required order of reaction can be obtained by the graphical analysis of your results. The first aliquot should be removed approximately 4 minutes after the reagents were mixed. You will then remove four further aliquots, at time intervals of your choice, up to a maximum time of 20 minutes. Prepare a table in the space provided on page 4 in which to record, to an appropriate level of precision, your chosen time, the actual time and your titration results for each of your aliquots. All values of actual time should be converted to decimal value, t, in minutes and record ed to one decimal place. For example if actual time = 4 min 33 s then t = 4 min + 33/60 min = 4.6 min

3 ASRJC JC2 PRELIMS 2019 9729/04/H2 [Turn over Experiment Safety: Propanone is flammable. Transfer your titrated solutions into the waste bottle for later disposal. Keep this bottle stoppered when not in use. Keep the conical flask (reaction mixture) stoppered except when removing aliquots. Preparing the boiling tubes 1. Label each of the boiling tubes with one of your chosen times. 2. Add approximately 10 cm3 of FA 5 to each of these boiling tubes. Preparing the reaction mixture 3. Using a pipette, transfer 25.0 cm3 of FA 1 into the 100 cm3 beaker. 4. Using a different pipette, transfer 25.0 cm3 of FA 2 into the same 100 cm3 beaker. 5. Using a burette, transfer 50.00 cm3 of FA 3 into the 250 cm3 conical flask, labelled reaction mixture. 6. Pour the contents of the 100 cm3 beaker into this 250 cm3 conical flask. Start the stopwatch, insert the stopper and swirl the mixture thoroughly. Once you have started the stopwatch, allow it to continue running for the duration of the experiment. You must not stop the stopwatch until you have collected all of your aliquots. Removing aliquots of reaction mixture 7. At approximately 4 minutes, using a 10.0 cm3 pipette, remove a 10.0 cm 3 aliquot of the reaction mixture. Immediately transfer this aliquot into the boiling tube labelled 4 minutes and swirl the mixture. Note the actual time when half of the reaction mixture has emptied from the pipette. Replace the stopper in the flask. 8. At each of your chosen times, repeat step 7 but transfer each aliquot to its appropriately labelled boiling tube. Titrations 9. Pour the whole of the contents of a boiling tube into a clean 250 cm 3 conical flask. Wash out the boiling tube and add the washings to the conical flask. 10. Titrate the iodine in this solution with FA 4. Add about 1 cm 3 of starch indicator when the colour of the solution turns pale yellow. The solution will turn blue–black. The end–point is reached when the dark blue–black colour just disappears. Record your results. 11. Empty the contents of this conical flask into the waste bottle. Wash this conical flask thoroughly with water. 12. Repeat steps 9 to 11 for each of your boiling tubes.

4 ASRJC JC2 PRELIMS 2019 9729/04/H2 (a) Results [3]

5 ASRJC JC2 PRELIMS 2019 9729/04/H2 [Turn over (b) (i) On Fig 1.1, plot a graph of volume of sodium thiosulfate, FA 4, on the y–axis, against time, t, on the x–axis. Start the x–axis at t = 0. You should choose a scale which will allow you to extrapolate your graph back to t = 0. Draw the most appropriate best–fit line taking into account all of your plotted points. Fig 1.1 [2]

6 ASRJC JC2 PRELIMS 2019 9729/04/H2 (ii) Deduce the order of reaction with respect to the I2 in reaction 1. Explain your answer. order................................................................................................................................ explanation...................................................................................................................... ......................................................................................................................................... ......................................................................................................................................... [1] (c) (i) Write the rate equation for the iodination of propanone. .................................................................................................................................... [1] (ii) Calculate the gradient of the line you have drawn in Fig 1.1 , showing clearly how you did this. gradient = ........................................ [1] (iii) Use your answer from (c)(ii) to determine the rate of change of amount of S 2O32– ions required in mol min–1. rate of change of amount of S2O32– ions required = ............................ mol min–1 [1] (iv) Hence, deduce the rate of disappearance of I2 in mol min–1. rate of disappeara