2022 RI H2Chem Prelims P4 Questions

© Raffles Institution 2022 9729/04/A/22 [Turn Over CANDIDATE NAME ( ) CLASS 22S0 RAFFLES INSTITUTION 2022 YEAR 6 PRELIMINARY EXAMINATION Higher 2 CHEMISTRY Paper 4 Practical 9729/04 24 August 2022 2 hours 30 minutes Do NOT turn over the Question Booklet until you are told to do so. READ THESE INSTRUCTIONS FIRST. Write your name and class on the space provided when instructed to do so. Give details of the practical shift and laboratory where appropriate, in the space provided. Write in dark blue or black pen. You may use a 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 number of marks is given in brackets [ ] at the end of each question or part question. 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 22 and 23. Shift Laboratory Bench Number For Examiner’s Use Question Marks 1 / 14 2 / 14 3 / 16 4 / 11 Total / 55 This document consists of 22 printed pages and 2 blank pages.

2 © Raffles Institution 2022 9729/04/A/22 Answer all the questions in the spaces provided. 1 Investigation of the effect of temperature on the rate of a reaction D-glucose, C6H12O6, is a sugar that can act as a reducing agent. In this question, you will investigate the effect of temperature on the rate of the redox reaction between acidified potassium manganate(VII) and D-glucose. FA 1 is 0.010 mol dm−3 potassium manganate(VII), KMnO4. FA 2 is 1.0 mol dm−3 sulfuric acid, H2SO4. FA 3 is 0.20 mol dm−3 D-glucose, C6H12O6. Initially, the reaction mixture is intensely purple. As the reaction proceeds, the intensity of the purple colour will decrease until the reaction mixture becomes colourless when the reaction is completed. The rate of the reaction is studied by measuring the time taken for the purple colour to disappear. You will perform a series of four experiments. Graphical analysis of your results will enable you to determine how temperature affects the rate of the reaction. For each experiment, you will measure and record the • time taken, t, in seconds for the reaction mixture to turn colourless, • initial temperature, Tinitial, and final temperature, Tfinal, in degree Celsius of the reaction mixture. You will then calculate values for • 1/t, • lg (1/t), • Tave, which is the average temperature of Tinitial and Tfinal in degree Celsius, • TK, which is the average temperature in kelvin (0 oC = 273 K), • 1/TK. (a) In Table 1.1 on page 4, record: • all values of t to the nearest second, • all values of Tinitial and Tfinal to an appropriate level of precision, • all calculated values of 1/t, lg (1/t), Tave, TK and 1/TK to three significant figures.

3 © Raffles Institution 2022 9729/04/A/22 [Turn Over Experiment 1 1. Fill the burette labelled FA 1, with FA 1. 2. Transfer 10.00 cm3 of FA 1 into a 100 cm3 conical flask. 3. Use a 50 cm3 measuring cylinder to transfer 25.0 cm3 of FA 2 into the conical flask containing FA 1. 4. Using a 25 cm3 measuring cylinder, measure 25.0 cm3 of FA 3. 5. Record the initial temperature, Tinitial, of the solution in the conical flask. 6. Add the FA 3 from the measuring cylinder into the conical flask. Start the stopwatch during this addition. 7. Mix the contents thoroughly by swirling the flask. Then place the flask on a white tile. 8. Stop the stopwatch as soon as the solution turns colourless. Record the final temperature, Tfinal, of the solution. 9. Record the time taken, t, to the nearest second. 10. Discard the reaction mixture. Wash out the conical flask and stand it upside down on a paper towel to drain. Experiment 2 11. Use the burette to transfer 10.00 cm3 of FA 1 into a 100 cm3 conical flask. 12. Use a 50 cm3 measuring cylinder to transfer 25.0 cm3 of FA 2 into the conical flask containing FA 1. 13. Place the conical flask on the tripod and heat its contents to between 55 oC and 65 oC. 14. When the temperature of the solution in the conical flask has reached between 55 oC and 65 oC, use a paper towel and carefully remove the conical flask from the Bunsen burner. 15. Repeat points 4 to 10 of Experiment 1. Experiments 3 and 4 Repeat points 11 to 15 of Experiment 2 two times, keeping the temperature of the contents of the conical flask between that of Experiment 1 and Experiment 2. You should ensure that there is a difference of at least 5 oC between each of the initial temperatures in all your experiments. You should alternate the use of the two 100 cm3 conical flasks. Record all temperatures, time taken and calculated values in Table 1.1.

4 © Raffles Institution 2022 9729/04/A/22 Table 1.1 expt Tinitial / oC Tfinal / oC t / s 1/t / s−1 lg (1/t) Tave / oC TK / K 1/TK / K−1 1 2 3 4 [3]

5 © Raffles Institution 2022 9729/04/A/22 [Turn Over (b) (i) Plot a graph of lg (1/t), on the y-axis, against 1/ TK, on the x-axis, on the grid in Fig. 1.1. Draw the best-fit straight line taking into account all of your plotted points. Extrapolate (extend) your line to 1/TK = 0.00340 K−1. [3] Fig. 1.1

6 © Raffles Institution 2022 9729/04/A/22 (ii) The clock reaction can be used as a timer, such that the time taken for the reaction mixture to turn colourless is 3 minutes. Use your graph to calculate the average temperature, Tave, at which this reaction should be carried out. Give your answer to one decimal place. Show on Fig. 1.1 how you obtained your answer. average temperature, Tave = ……………… oC [2] (c) In an experiment, it was found that 1 mol of acidified potassium manganate(VII), KMnO4, oxidised 2.5 mol of D-glucose. The half-equation for the reduction of MnO4− under acidic conditions is given below. MnO4− + 8H+ + 5e− ⎯→ Mn2+ + 4H2O (i) Calculate the amount of electrons lost per mole of D-glucose. amount of electrons lost per mole of D-glucose = ………………. mol [1]

7 © Raffles Institution 2022 9729/04/A/22 [Turn Over (ii) The structure of D-glucose is shown in Fig. 1.2. D-glucose P Fig. 1.2 Given that only one carbon atom in D-glucose is oxidised, suggest a structure of the organic product P formed from the oxidation of D-glucose. Draw your structure of P on Fig. 1.2. Explain your answer by describing the change in oxidation state of the carbon atom which has undergone oxidation. …………………………………………………………………………………..…….......... …………………………………………………………………………………..…….......... …………………………………………………………………………………..…….......... …………………………………………………………………………………..…….......... …………………………………………………………………………………..…….......... …………………………………………………………………………………………… [2] (d) (i) The uncertainty (error) associated with each reading using either a 25 cm 3 or 50 cm3 measuring cylinder is 0.5 cm3. Calculate the maximum total percentage uncertainty (error) in the total volume of the reaction mixture for Experiment 1. maximum t