Sodium thiosulfate reacts with excess dilute hydrochloric acid according to the following equation. Na₂S₂O₃(aq) + 2HCl(aq) → 2NaCl(aq) + S(s) + SO₂(g) + H₂O(l) The reaction produces sulfur dioxide which is corrosive and toxic by inhalation. The effect of temperature on the rate of this reaction can be investigated by the 'disappearing cross experiment' as follows. step 1 Measure 10.00 cm³ of 0.100 mol dm⁻³ Na₂S₂O₃(aq) and transfer into a boiling tube. step 2 Into a second boiling tube, transfer 10 cm³ of 0.500 mol dm⁻³ HCl(aq). step 3 Heat both tubes in the same water-bath. step 4 Place a conical flask on a piece of paper, on which is drawn a large X. step 5 When the solutions reach the required temperature, remove them from the water-bath, pour the contents of both tubes into the conical flask and immediately start a timer. step 6 The X on the paper should be viewed from above the flask as shown in the diagram. step 7 When the X can no longer be seen, due to formation of solid sulfur, stop the timer. step 8 Repeat the experiment using the same volumes and concentrations of solution at different temperatures. [Figure X.X]

1. (a)State one precaution that should be taken to reduce a hazard caused by one of the products of this reaction. [1][1]
2. (b)Suggest appropriate equipment for measuring the required volumes of Na₂S₂O₃(aq) and HCl(aq) stated in the method. Na₂S₂O₃(aq) .............................................................................................................................................. HCl(aq) ..................................................................................................................................................... [1][1]
3. (c)Complete column E in the table, giving your values to three significant figures. [1][1]
4. (d)(i)Plot a graph of 2.303 log (1/t) on the y-axis and 1/T on the x-axis. Draw a line of best fit. [2][2]
5. (d)(ii)Circle the point on the graph you consider to be most anomalous. Suggest two possible errors in how the procedure was carried out which could have caused this anomalous point. 1 ................................................................................................................................................................................................................... 2 ................................................................................................................................................................................................................... [2][2]
6. (d)(iii)Use the graph to determine the gradient of the line of best fit. State the coordinates of both points you used in your calculation. These must be selected from your line of best fit. Give the gradient to three significant figures. coordinates 1 ..................................................................... coordinates 2 ..................................................................... gradient = .......................................................... K [2][2]
7. (d)(iv)Use the gradient you have calculated and the equation to calculate Eₐ, in kJ mol⁻¹, for the reaction. Give your answer to two significant figures. Include a sign. Eₐ = ..................................................... kJ mol⁻¹ [3][3]
8. (e)A student repeats the experiment at 60°C but with a different concentration of Na₂S₂O₃(aq). The new solution is named solution B. The time taken until X can no longer be seen is 11.52s. Assume no error was made in the timing. State whether the concentration of solution B is more or less than 0.10 mol dm⁻³. Explain your answer. [1][1]
9. (f)It is more appropriate for the values in column C of the table on page 6 to be recorded to the nearest second. Suggest one reason for this. [1][1]

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