Quantitative Analysis 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. 1 You will investigate how increasing temperature affects the rate of a reaction. Sodium thiosulfate reacts with acid to form a pale yellow precipitate of sulfur. The ionic equation for the reaction is given. S2O32-(aq) + 2H+(aq) → S(s) + SO2(g) + H₂O(I) You will measure the time it takes for the sulfur formed in the reaction to obscure the print on the Insert supplied. Record your results in a table on page 4. Your table should include the rate of reaction for each experiment. FA 1 is an 18.1gdm-³ solution of hydrated sodium thiosulfate, Na2S2O3.5H2O. FA 2 is a 0.050 mol dm³ solution of a strong monoprotic acid, HZ. (a) Method • Approximately half fill the 250 cm³ beaker with tap water and place it on the tripod and gauze over the Bunsen burner. • Heat the water in the beaker to about 55°C and then switch off the Bunsen burner. This will be your hot water bath. • Use the 25 cm³ measuring cylinder to transfer 10cm³ of FA 1 into boiling tube 1. Place boiling tube 1 into your hot water bath. • Use the 50 cm³ measuring cylinder to transfer 20 cm³ of FA 2 into boiling tube 2. Place boiling tube 2 into your hot water bath. • Leave boiling tubes 1 and 2 in the hot water bath to heat up for use in Experiment 2. • Start Experiment 1. Experiment 1 • Use the 50 cm³ measuring cylinder to transfer 20 cm³ of FA 2 into the 100 cm³ beaker. • Measure and record the temperature of FA 2. • Use the 25 cm³ measuring cylinder to transfer 10cm³ of FA 1 into the same beaker and start timing immediately. • Swirl the beaker once to mix the solutions and place the beaker on the Insert. • Look down through the beaker and contents onto the Insert. • Stop timing as soon as the precipitate of sulfur obscures the print on the Insert. • Record the reaction time to the nearest second. • Empty the contents of the beaker into the quenching bath. • Rinse and dry the beaker so it is ready for use in Experiment 2. Experiment 2 • Measure and record the temperature of FA 2 in boiling tube 2. • Carefully transfer the hot contents of boiling tube 2 into the 100 cm³ beaker. • Carefully transfer the hot contents of boiling tube 1 into the same beaker and start timing immediately. • Swirl the beaker once to mix the solutions and place the beaker on the Insert. • Look down through the beaker and contents onto the Insert. • Stop timing as soon as the precipitate of sulfur obscures the print on the Insert. • Record the reaction time to the nearest second. • Empty the contents of the beaker into the quenching bath. • Rinse and dry the beaker so it is ready for use in Experiment 3. Experiment 3 • Use the 25 cm³ measuring cylinder to transfer 10cm³ of FA 1 into boiling tube 1. Place boiling tube 1 into your hot water bath. • Use the 50 cm³ measuring cylinder to transfer 20 cm³ of FA 2 into boiling tube 2. Place boiling tube 2 into your hot water bath. • Place the thermometer in boiling tube 2. When the temperature of FA 2 is about 8 °C lower than that for Experiment 2 record the temperature. Remove the thermometer and transfer the contents of boiling tube 2 into the 100 cm³ beaker. • Transfer the contents of boiling tube 1 into the same beaker and start timing immediately. • Swirl the beaker once to mix the solutions and place the beaker on the Insert. • Look down through the beaker and contents onto the Insert. • Stop timing as soon as the precipitate of sulfur obscures the print on the Insert. • Record the reaction time to the nearest second. • Empty the contents of the beaker into the quenching bath. • Rinse and dry the beaker so it is ready for use in Experiments 4 and 5. Experiments 4 and 5 • Repeat the method for Experiment 3 but at two different temperatures. • Keep the temperature of FA 2 between room temperature and 55°C. Do not exceed 55°C. Record all your results in your table on page 4.

1. (a)Results The rate of reaction can be calculated as shown. rate = 1000 / reaction time Calculate the rate of reaction for each of your five experiments. Record these rates in your table. [Figure 1a-table][8]
2. (b)On the grid plot a graph of rate of reaction on the y-axis, starting at zero, against temperature on the x-axis. Select a scale for the x-axis which includes a temperature of 15.0°C. Label your axes and any points you consider anomalous. Draw a line of best fit and extrapolate it to 15.0°C. [Figure 1b-graph][4]
3. (c)Use your graph to calculate the time to the nearest second that the reaction would have taken if you had carried it out at 17.5°C. Show on the grid how you obtained your answer. time = .............................................. s[2]
4. (d)Explain, by referring to your graph or your table of results, how the rate of reaction is affected by increasing temperature.[2]
5. (e)(i)Calculate the concentration of hydrated sodium thiosulfate, Na2S2O3.5H2O, in FA 1 in mol dm-3. concentration of Na2S2O3.5H2O in FA 1 = .............................................. mol dm-³[1]
6. (e)(ii)Calculate the concentration of the strong monoprotic acid, HZ, in the solution immediately after FA 1 was added to FA 2 in the beaker. concentration of HZ = .............................................. mol dm-³[1]
7. (e)(iii)Use the equation on page 2 to determine which reagent, FA 1 or FA 2, was in excess. The reagent in excess was ..............................................[2]
8. (f)(i)Calculate the maximum percentage error in measuring the reaction time you recorded for Experiment 2. Assume that the maximum error of the timer is ±0.5s. maximum percentage error in the reaction time = .............................................. %[1]
9. (f)(ii)A student suggested that the error in measuring the reaction time in Experiment 1 was greater than for Experiment 2. Give one reason why the student could be correct.[1]
10. (g)Suggest two ways to improve the accuracy of the results of these experiments. 1 ....................................................................................................................................................... 2 .......................................................................................................................................................[2]

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