2019 VJC H2 Chem Prelim P4 Ans

1  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 cm 3 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 either a cloth or 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.

2  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 cm 3 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