CIE Jun 2017 v5 Paper 3 Q1

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Sulfur forms the peroxodisulfate anion, S2O8 shown in the equation. 2. This ion can oxidise iodide ions, I, to iodine, I2, as PMT 2I(aq) + S2O8 2(aq) I2(aq) + 2SO4 2(aq) You will carry out a series of experiments to investigate how the rate of this reaction is affected by changing the concentration of the solutions. The rate can be measured by adding thiosulfate ions, S2O3 between S2O8 2 and I occurs iodine is produced, but it reacts immediately with the thiosulfate. 2, and starch indicator. As the reaction I2(aq) + 2S2O3 2(aq) 2I(aq) + S4O6 2(aq) When all the thiosulfate has reacted, the iodine will remain in the mixture and cause the starch indicator to turn blue-black. The rate of reaction may be determined by timing how long it takes the reaction mixture to turn blue-black. FA 1 is 0.0200 mol dm3 potassium peroxodisulfate, K2S2O8. FA 2 is 1.00 mol dm3 potassium iodide, KI. FA 3 is 0.00500 mol dm3 sodium thiosulfate, Na2S2O3. starch indicator Read through the instructions carefully and prepare a table for your results on page 4 before starting any practical work. (a) Method Experiment 1Fill the burette labelled FA 1 with FA 1. Use the pen to label one of the 100 cm3 beakers A and the other 100 cm3 beaker B. Run 20.00 cm3 of FA 1 from the burette into beaker A. Use the measuring cylinder to add 20.0 cm3 of FA 2 into beaker B. Use the measuring cylinder to add 10.0 cm3 of FA 3 to beaker B. Add 10 drops of starch indicator to beaker B. Add the contents of beaker A to beaker B and start timing immediately. Stir the mixture once and place the beaker on a white tile. Stop timing as soon as the solution turns blue-black. Record this reaction time to the nearest second in your results table. Wash out both beakers and shake to remove excess water. Experiment 2Fill a second burette with distilled water. Run 10.00 cm3 of FA 1 into beaker A. Run 10.00 cm3 of distilled water into beaker A. Use the measuring cylinder to add 20.0 cm3 of FA 2 into beaker B. Use the measuring cylinder to add 10.0 cm3 of FA 3 to beaker B. Add 10 drops of starch indicator to beaker B. Add the contents of beaker A to beaker B and start timing immediately. Stir the mixture once and place the beaker on a white tile. Stop timing as soon as the solution turns blue-black. Record this reaction time to the nearest second in your results table. Wash out both beakers and shake to remove excess water.UCLES 2017 9701/35/M/J/17 [Turn over<br /> PMT Experiments 3-5 Carry out three further experiments to investigate how the reaction time changes with different volumes of potassium peroxodisulfate, FA 1. Note that the combined volume of FA 1 and distilled water must always be 20.00 cm3. Do not use a volume of FA 1 that is less than 6.00 cm3. Keep FA 1, FA 2, FA 3 and the starch indicator for use in (e). Calculating the rate of the reaction The rate of the reaction can be represented by the formula shown. rate = 500 reaction time in seconds Use this formula to calculate the rate for each of your five experiments. Record all your results in a single table. You should include the volume of FA 1, the volume of distilled water, the reaction time and the reaction rate for each of your five experiments. II III IV VI VII VIII IX [10] (b) On the grid on page 5, plot the rate (y-axis) against the volume of FA 1 (x-axis). Include the origin in your plot. Draw a straight line of best fit and circle any clearly anomalous points.UCLES 2017 9701/35/M/J/17<br /> PMT II III IV [4] [Turn overUCLES 2017 9701/35/M/J/17<br /> PMT (c) The volume of FA 1 is directly related to the concentration of potassium peroxodisulfate. From your results, what can be stated about the relationship between the rate of reaction and the concentration of potassium peroxodisulfate?[1] (d) (i) Use your graph to calculate the reaction time you would expect to measure if you carried out an experiment using 5.00 cm3 of FA 1. Show your working. (ii) Assume that the error in the time measured for each reaction was0.5 s in total. Calculate the maximum percentage error in the reaction time you measured in Experiment 1. Show your working. reaction time =s maximum percentage error =% (iii) A student suggested that this error could be reduced if 0.0100 mol dm3 sodium thiosulfate were used in place of FA 3. Do you agree with this student? Explain your answer.(iv) A student repeated Experiment 1 but used 0.100 mol dm3 sodium thiosulfate in place of FA 3. The student found that the reaction mixture never turned blue-black. Explain why.[5]UCLES 2017 9701/35/M/J/17<br /> (e) (i) Using the same method as in (a), carry out an additional experiment to record the reaction time to the nearest second when the following solutions are mixed together. PMT10.00 cm3 of FA 120.0 cm3 of FA 25.0 cm3 of FA 315.00 cm3 of distilled water10 drops of starch indicator (ii) Use your answer to (i) to estimate the reaction time that would be measured if the following solutions were mixed together. reaction time =DO NOT CARRY OUT THIS EXPERIMENT10.00 cm3 of FA 120.0 cm3 of FA 220.0 cm3 of FA 310 drops of starch indicator Explain your answer. estimated reaction time =[4] [Total: 24]UCLES 2017 9701/35/M/J/17 [Turn over<br />

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