2023 JPJC J2 H2 Prelim Paper 4 Qn Paper

 Jurong Pioneer Junior College [Turn Over NAME CLASS 22S JURONG PIONEER JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION 2023 CHEMISTRY 9729/04 Higher 2 Paper 4 Practical 15 August 2023 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 exam 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 HB pencil for any diagrams, 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. Shift At the end of the examination, fasten all your work securely together. Laboratory The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 15 2 13 3 17 4 10 Total 55 This document consists of 22 printed pages and 2 blank pages.

2  Jurong Pioneer Junior College 9729/04/J2 PRELIMINARY EXAM/2023 Answer all the questions in the spaces provided. 1 Determination of the kinetics of the reaction between iodide ions and peroxodisulfate ions FA 1 is 0.0200 mol dm–3 potassium peroxodisulfate, K2S2O8. FA 2 is 1.00 mol dm–3 potassium iodide, KI. FA 3 is 0.00500 mol dm–3 sodium thiosulfate, Na2S2O3. starch indicator. Equation 1 represents the reaction between peroxodisulfate ions, S 2O8 2, and iodide ions, I–. equation 1 S2O8 2(aq) + 2I–(aq)  2SO4 2(aq) + I2(aq) When starch is added to the reaction mixture, a blue-black colour is immediately seen due to the formation of an iodine-starch complex. If a small amount of sodium thiosulfate, Na2S2O3, is also present in the reaction mixture, the formation of the blue-black colour is delayed. The Na 2S2O3 reacts with I2 as shown in equation 2. equation 2 I2(aq) + 2S2O3 2–(aq) → 2I–(aq) + S4O6 2–(aq) You will perform a series of five experiments. Then you will graphical ly analyse your results in order to determine the order with respect to the concentration of the peroxodisulfate ions, [S2O8 2]. For each experiment, you will note the volume of FA 1 added, VFA1, and the time taken, t, for the reaction mixture to turn blue-black. In each experiment, you will add a fixed amount of sodium thiosulfate, FA 3, to each of your experiments. 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,  lg(1/ t),  lg( VFA1) For Examiner’s Use Prepare a table in the space provided on page 4 in which to record, to an appropriate level of precision:  all volumes, except the volumes of FA 2, FA 3 and starch indicator,  all values of t,  all calculated values of 1/ t, lg(1/t), lg(VFA1) to 3 significant figures.

3  Jurong Pioneer Junior College 9729/04/J2 PRELIMINARY EXAM/2023 [Turn Over BLANK PAGE

4  Jurong Pioneer Junior College 9729/04/J2 PRELIMINARY EXAM/2023 (a) Experiment 1 1. Fill the burette labelled FA 1, with FA 1. 2. Run 20.00 cm 3 of FA 1 into a 100 cm3 beaker labelled Beaker A. 3. Using appropriate measuring cylinders, add the following to the second 100 cm3 beaker labelled Beaker B:  20.0 cm 3 of FA 2  10.0 cm 3 of FA 3 4. Add 10 drops of starch indicator to Beaker B. 5. Add the contents of Beaker A to Beaker B and start timing immediately. 6. Stir the mixture thoroughly using the glass rod and place the beaker on a white tile. 7. Stop timing as soon as the solution turns blue-black. 8. Record the time taken, t, to the nearest 0.1 s in your table. 9. Wash out both beakers thoroughly with water and shake dry. Rinse and dry the glass rod. Experiments 2 to 5 Repeat experiment 1 four times, adding 18.00, 14.00, 10.00 and 6.00 cm 3 respectively, of FA 1 at point 2. In each case, you will need to ensure that the same total volume of the reaction mixture is used by adding deionised water as required using the second burette provided. Record all required volumes, time taken and calculated values in your table. For Examiner’s Use Results [4]

5  Jurong Pioneer Junior College 9729/04/J2 PRELIMINARY EXAM/2023 [Turn Over (b) (i) Plot a graph of lg( 1/t) on the y-axis against lg( VFA1) on the x-axis. Draw the best-fit straight line taking into account all of your plotted points. For Examiner’s Use [3] (b) (ii) Calculate the gradient of the line to three significant figures, showing clearly how you did this. Hence, deduce the order of the reaction wit h For Examiner’s Use

6  Jurong Pioneer Junior College 9729/04/J2 PRELIMINARY EXAM/2023 respect to [S2O8 2]. Gradient = ……………………………… Order = ……………………………… [3] (c) (i) A student thought that the experiment could be made more accurate by having longer reaction times. To do this, he repeated Experiment 1 w ith the same volumes but using 0.100 mol dm–3 sodium thiosulfate instead of FA 3. He found that the reaction never turned blue-black. Explain why. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. [1] (ii) Other than errors involving measurements of volume and time, suggest an additional source of error in these experiments and what improvement could be made to reduce this error. Error: ………………………………………………………………….………… ……………………………………………………………………………………. ……………………………………………………………………………………. Improvement: …………………………………………………………….……. ……………………………………………………………………………………. ……………………………………………………………………………………. [2] (d) (i) The experimental method can be modified to enable the rate of reaction with respect to [I–] to be investigated. For Examiner’s Use

7  Jurong Pioneer Junior College 9729/04/J2 PRELIMINARY EXAM/2023 [Turn Over Equation 1 S2O8 2(aq) + 2I–(aq)  2SO4 2(aq) + I2(aq) In the first line in Table 1.1 below, the volumes of FA 1, FA 2, FA 3 and deionised water used in Experiment 1 are recorded. Complete the following table, suggesting volumes for each of the reagents that could be used in one further experiment to investigate how the rate of reaction varies with a change in volume of potassium iodide, FA 2. Do not carry out this experiment. Table 1.1 Experiment VFA1/ cm3 VFA2/ cm3 VFA3/ cm3 Vwater/ cm3 1 20 20 10 0 6 [1] (ii) The overall order for the reaction in equation 1 is second order. Using your answer in 1(b)(ii), write a rate equation for the reaction. ……………………………………………………………………………………. [1] [Total: 15] 2. Determination of the percentage of mass of copper in FA 4 For Examiner’s Use

8  Jurong Pioneer Junior College 9729/04/J2 PRELIMINARY EXAM/2023 When excess of potassium iodide, KI, is added to the solution of Cu2+ ions, iodine, I2, and a precipitate of CuI is produced. The I2 turns the solution brown. equation 3 2Cu2+ + 4I  2CuI + I2 I2 has a relatively low solubility in water. However, the presence of an excess o f I ions in the reaction mixture allows the soluble tri-iodide ion, I3 , to form as shown by equation 4. This ensures that the I2 formed as shown in equation 3 is fully dissolved. equation 4 I2 + I   I3  The I3