CIE Nov 2017 v4 Paper 3 Q1

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PMT Sodium thiosulfate reacts with acid to produce a pale yellow precipitate of sulfur. S2O3 2(aq) + 2H+(aq) S(s) + SO2(aq) + H2O(l) You will investigate how the rate of this reaction varies with the concentration of thiosulfate ions. To do this you will measure the time taken for a fixed amount of sulfur to be formed. FB 1 is 0.10 mol dm3 sodium thiosulfate, Na2S2O3. FB 2 is 1.00 mol dm3 hydrochloric acid, HCl. (a) Method Read through the instructions and prepare a table on page 3 for your results before starting any practical work. You will need to include volume of FB 1, volume of water, reaction time and rate of reaction for each of the five experiments. Experiment 1Use the larger measuring cylinder to transfer 40 cm3 of FB 1 into the 100 cm3 beaker. Use the smaller measuring cylinder to measure 25 cm3 of FB 2. Pour the FB 2 into the FB 1 in the beaker and start timing immediately. Stir the mixture in the beaker once and place the beaker on top of the printed insert provided. Look down through the solution in the beaker at the print on the insert. Stop timing as soon as the precipitate of sulfur makes the print on the insert just invisible. Record the reaction time to the nearest second. Empty, rinse and dry the beaker so it is ready for use in Experiment 2. Rinse the sink with tap water to wash away the products of the reaction. Experiment 2Use the larger measuring cylinder to transfer 30 cm3 of FB 1 into the 100 cm3 beaker. Use the same measuring cylinder to add 10 cm3 of distilled water to the beaker. Use the smaller measuring cylinder to add 25 cm3 of FB 2 to the mixture in the beaker and start timing immediately. Stir the mixture in the beaker once and place the beaker on top of the printed insert provided. Look down through the solution in the beaker at the print on the insert. Stop timing as soon as the precipitate of sulfur makes the print on the insert just invisible. Record the reaction time to the nearest second. Empty, rinse and dry the beaker so it is ready for use in Experiment 3. Rinse the sink with tap water to wash away the products of the reaction.UCLES 2017 9701/34/O/N/17<br /> PMT Experiment 3 Repeat Experiment 2 using 20 cm3 of FB 1, 20 cm3 of distilled water and 25 cm3 of FB 2. Experiments 4 and 5 Choose suitable volumes that will enable you to investigate further the effect of changing the concentration of thiosulfate ions on the rate of the reaction. You should not use a volume of less than 10 cm3 of FB 1. Results The rate of the reaction can be calculated as shown. rate = 1000 reaction time Calculate the rate of reaction for each experiment and complete the table. II III IV VI VII VIII IX [10]UCLES 2017 9701/34/O/N/17 [Turn over<br /> (b) On the grid plot a graph of rate of reaction (y-axis) against volume of FB 1 (x-axis). Circle any points that you consider anomalous and draw a line of best fit to show how the rate of the reaction depends on the volume of FB 1. PMT (c) Use your graph to calculate the time that the reaction would have taken if 8 cm3 of FB 1 had been used. Show on the grid how you obtained your answer. [3]UCLES 2017 9701/34/O/N/17 time =s [2]<br /> (d) (i) A student broke the 100 cm3 beaker when carrying out the experiment and decided to use a petri dish instead. This has a different shape. PMT beaker petri dish State and explain what effect this would have on the students results.(ii) Another student suggested that the experiment could be improved by using a less concentrated solution of sodium thiosulfate. Explain whether this suggestion would improve the accuracy of the results.[4] (e) Calculate the maximum percentage error in the reaction time for Experiment 1. Show how you obtained your answer. maximum percentage error =% [1] (f) Using a similar method to (a), explain how you would investigate how the rate of the reaction varies with changes in the concentration of hydrochloric acid.[3]UCLES 2017 9701/34/O/N/17 [Turn over<br /> (g) An experiment to investigate the effect of changing the concentration of hydrochloric acid gave results that could be plotted to produce a graph. On the axes, sketch the graph that would show that: (i) the rate of reaction was directly proportional to the concentration of acid, PMT rate of reaction (ii) the rate of reaction did not depend on the concentration of acid. concentration of acid rate of reaction concentration of acid [2] [Total: 25]UCLES 2017 9701/34/O/N/17<br />

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