In a neutral solution, aqueous potassium iodide acts as a catalyst for the decomposition of aqueous hydrogen peroxide. 2H2O2(aq) → 2H2O(l) + O2(g) A student plans to carry out an investigation to find how temperature affects the initial rate of the decomposition of aqueous hydrogen peroxide, H2O2(aq), in the presence of aqueous potassium iodide, KI(aq). The student knows that the initial rate of the reaction can be measured by timing the production of the oxygen. The student carries out a series of experiments. In experiment 1 the student notes the temperature of the H2O2(aq) and KI(aq) under room conditions. The solutions are mixed in apparatus designed to collect the oxygen produced. A stop-watch is started at the beginning of the reaction. The volume of oxygen is noted at regular time intervals. In experiments 2–8 the solutions are heated to different temperatures before mixing and measurement of the oxygen produced. The data collected is used to determine a value for the activation energy of the decomposition of H2O2(aq) in the presence of KI(aq).

1. (a)State the independent variable.[1]
2. (b)State two variables that need to be controlled. 1 2[2]
3. (c)(i)State how the student should prepare 250.0 cm³ of 0.100 mol dm⁻³ H2O2(aq) from 0.500 mol dm⁻³ H2O2(aq). Calculate the minimum volume of 0.500 mol dm⁻³ H2O2(aq) required for preparation of the 0.100 mol dm⁻³ H2O2 solution. Give the name and capacity of any key apparatus which should be used. Write your answer as a series of numbered steps.[3]
4. (c)(ii)Hydrogen peroxide causes eye and skin irritation. State what precaution should be taken when preparing the solution in (c)(i) other than wearing goggles.[1]
5. (d)(i)The student performs experiments 1–8 using a range of temperatures. The results are shown in Table 2.1. Complete the table and record the values of 1/T to three significant figures and the values of log initial rate to three significant figures. Table 2.1 experiment number temperature /°C temperature /K 1/T /K⁻¹ initial rate /mol s⁻¹ log initial rate 1 20 293 5.75 × 10⁻⁶ 2 25 298 7.94 × 10⁻⁶ 3 30 303 1.17 × 10⁻⁵ 4 35 308 1.45 × 10⁻⁵ 5 39 312 2.19 × 10⁻⁵ 6 46 319 3.72 × 10⁻⁵ 7 52 325 5.25 × 10⁻⁵ 8 55 328 6.31 × 10⁻⁵[2]
6. (d)(ii)Plot a graph on the grid to show the relationship between log initial rate and 1/T. Use a cross (x) to plot each data point. Draw a line of best fit.[2]
7. (d)(iii)Circle the point on the graph you consider to be most anomalous. Suggest one reason why this anomaly may have occurred during this experimental procedure.[2]
8. (d)(iv)Determine the gradient of your 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]
9. (d)(v)The relationship between log initial rate and 1/T is given by the expression: log initial rate = constant – Ea / (2.303 RT) Use the gradient calculated in (d)(iv) to calculate a value for the activation energy, Ea. (If you were unable to obtain an answer to (d)(iv) you may use the value –3100 K. This is not the correct value.) Ea = kJ mol⁻¹[2]
10. (e)It is not possible to repeat the investigation. State whether the data from the investigation is reliable. Justify your answer.[1]