2019 VJC H2 Chem Prelim P4 QP

2  VJC 2019 9729/04/PRELIM/19 [Turn over Answer all the questions in the spaces provided. 1 Determination of the dependence of the rate of reaction between glucose and acidified potassium manganate(VII) on temperature 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. Glucose, C6H12O6, is a sugar that can act as a reducing agent. You will investigate how an increase in temperature affects the rate of the redox reaction between glucose and acidified potassium manganate(VII). FA 1 is 0.020 mol dm–3 acidified potassium manganate(VII), KMnO4. FA 2 is 1.0 mol dm–3 sulfuric acid, H2SO4. FA 3 is an aqueous solution containing 32.8 g dm–3 glucose, C6H12O6. FA 4 is a solid mixture containing an unknown percentage of glucose. You will measure the time it takes for the purple colour to disappear. Your table of results on the following page should include the rate of reaction for each experiment. (a) Method Experiment 1 1. Fill the burette with FA 1. 2. Add 5.00 cm3 of FA 1 into the 250 cm3 beaker. 3. Use the 50 cm 3 measuring cylinder to transfer 50.0 cm3 of FA 2 into the beaker containing FA 1. 4. Use the same measuring cylinder to transfer 50.0 cm3 of distilled water into the same beaker. 5. Place the beaker on the tripod and heat its contents to between 75 C and 80 C. 6. While the solution in the beaker is being heated, pour 25.0 cm3 of FA 3 into the 25 cm3 measuring cylinder. 7. When the temperature of the contents of the beaker has reached between 75 C and 80 C, turn off the Bunsen burner and carefully hold the top of the hot beaker with a paper towel and place it onto the white tile. 8. Record the temperature of the solution in the beaker. 9. Add the 25.0 cm3 of FA 3 and immediately start timing. 10. Stir the contents of the beaker once and stop timing as soon as the solution turns colourless. Record the time to the nearest second. 11. Record the temperature of the solution as soon as it is colourless. 12. Calculate and record the average temperature of the reaction mixture to one decimal place. 13. Empty, rinse and dry the beaker so it is ready for use in Experiment 2.

3  VJC 2019 9729/04/PRELIM/19 [Turn over Experiment 2 1. Add 5.00 cm3 of FA 1 into the 250 cm3 beaker. 2. Use the 50 cm 3 measuring cylinder to transfer 50.0 cm3 of FA 2 into the beaker containing FA 1. 3. Use the same measuring cylinder to transfer 50.0 cm3 of distilled water into the same beaker. 4. Place the beaker on the tripod and heat its contents to between 35 C and 40 C. 5. While the solution in the beaker is being heated, pour 25.0 cm3 of FA 3 into the 25 cm3 measuring cylinder. 6. When the temperature of the contents of the beaker has reached between 35 C and 40 C, turn off the Bunsen burner and carefully hold the top of the hot beaker with a paper towel and place it onto the white tile. 7. Record the temperature of the solution in the beaker. 8. Add the 25.0 cm3 of FA 3 and immediately start timing. 9. Stir the contents of the beaker once and stop timing as soon as the solution turns colourless. Record the time to the nearest second. 10. Record the temperature of the solution as soon as it is colourless. 11. Calculate and record the average temperature of the reaction mixture to one decimal place. 12. Empty, rinse and dry the beaker so it is ready for use in Experiment 3. Experiments 3, 4 and 5 1. Repeat the method for Experiment 2 at three different temperatures. 2. Keep the temperature of the contents of the beaker between room temperature and 80 C. 3. Record all your results in your table. Results: The rate of reaction can be calculated as shown. rate = 1000 reaction time Calculate the rate of reaction for each experiment and include this in your table. [5]

4  VJC 2019 9729/04/PRELIM/19 [Turn over (b) Plot a graph of rate ( y-axis) against average temperature ( x-axis) on the grid below. Select a scale on the x-axis to in clude an average temperature of 30.0 C. Label any points you consider anomalous. Draw the most appropriate best-fit curve taking into account all of your plotted points and extrapolate it to 30.0 C. [3] (c) Use your graph to calculate the time to the nearest second that the reaction would have taken if the average temperature had been 52.5oC. Show on the grid how you obtained your answer. time =……………… [2]

5  VJC 2019 9729/04/PRELIM/19 [Turn over (d) Explain, by referring to your graph or your table of results, how the rate of reaction is affected by an increase in temperature. ………………………………………………………………………………..………………….. ………………………………………………………………………………..………………….. ………………………………………………………………………………..………………….. ………………………………………………………………………………..………………..[1] (e) (i) Calculate the maximum percentage error in the reaction time recorded for Experiment 1. Assume the error of the timer is ±1 s. maximum percentage error in Experiment 1 =……………… [1] (ii) You have carried out experiments at five different temperatures. Identify an experiment, if any, you should have repeated. Give a reason for your answer. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………..[1] (iii) Suggest one way to improve the accuracy of the results for this investigation. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………..[1] (f) (i) Calculate the concentration of glucose in FA 3 in mol dm–3. concentration of glucose in FA 3 =……………… [1]

6  VJC 2019 9729/04/PRELIM/19 [Turn over (ii) Calculate the volume of 0.02 0 mol dm –3 acidified KMnO4 that would react with all the glucose present in 25.0 cm3 of FA 3. 5C6H12O6 + 24MnO4– + 72H+  30CO2 + 24Mn2+ + 66H2O Volume of acidified KMnO4 required =……………… [2] (iii) Comment on the feasibility of conducting a redox titration between the given concentration of glucose and acidified KMnO4. ………………………………………………………...………………………………….. ………………………………………………………...………………………………….. ………………………………………………………...………………………………….. ………………………………………………………...………………………………..[1] (g) Determination of the percentage of glucose in FA 4 by titration 1. Weigh accurately 1.5 g of FA 4 in a weighi ng bottle. Record your weighing appropriately in the space below. If you use TARE facility of the balance, please indicate clearly in your recording. 2. Dissolve the solid in a beaker and quantitatively transfer into a 250 cm 3 volumetric flask. Make up to the mark with distilled water. Label this FA 4 solution. 3. Pipette 25.0 cm3 of FA 4 solution into a conical flask. 4. Using a measuring cylinder add 50.0 cm3 of FA 2 into the conical flask. 5. Place the conical flask on the tripod and heat its contents to between 75 C and 80 C. 6. When the temperature of the contents of the conical flask has reached between 75 C and 80 C, turn off the Bunsen burner and carefully hold the neck of the conical flask with a paper towel. 7. Titrate with FA 1 until a permanent colour change is observed. 8. Record the burette readings in the suitable format. Repeat titration to achieve consistent results.

7  VJC 2019 9729/04/PRELIM/19 [Turn over Results: Weighing of FA 4 Titration [5] (h) (i) From your titrations, obtain a suitable volume of FA 1 to be used in your calculations. Show clearly how you obtained this volume. volume of FA 1 = …………………..