19 Turn over 6 Aqueous hydrogen peroxide decomposes according to the following equation. 2H2O2(aq)  →  2H2O(l)  +  O2(g) The decomposition is catalysed by manganese(IV) oxide. This can be investigated by measuring the volume of oxygen produced at various times as the reaction proceeds. Part of the apparatus used in the experiment is shown. The manganese(IV) oxide is placed in a small glass container, which is then tipped over to start the reaction. A stop clock is started at the same time. (a) Complete the diagram to show how the gas can be collected and its volume measured, labelling the apparatus used. (2) aqueous hydrogen peroxide manganese(IV) oxide 20 (b) An experiment was carried out using 0.25 g of manganese(IV) oxide granules and 50 cm3 of aqueous hydrogen peroxide of concentration 0.16 mol dm−3. The results are shown in the table and plotted on a graph. Time / s 0.0 20.0 30.0 50.0 60.0 80.0 100 120 150 Volume of O2 / cm3 0 51 68 85 88 91 92 92 92 120 100 80 60 40 20 0 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 Time / s Volume / cm3 (i) The rate of reaction may be assumed to be approximately constant up to the first volume measurement (20.0 s in this experiment). Use this approximation to calculate the initial rate of this reaction, giving the units with your answer. (1) 21 Turn over (ii) Draw a tangent at 40 s on the graph on Page 20 and use it to calculate the rate of reaction at this time. (2) (iii) The experiment was repeated on a different day when the laboratory was 20 °C warmer. The volume of oxygen was recorded for the same total time of 150 s. Draw the line that you would expect to obtain in this experiment. Assume the pressure in the laboratory is the same. No calculation is required. (2) 120 100 80 60 40 20 0 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 Time / s Volume / cm3 22 (iv) Explain, using collision theory, any differences between the line you have drawn and the original line of best fit. 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(c) Catalysts are not used up during a reaction. Manganese(IV) oxide acts as a heterogeneous catalyst. Describe in outline a method to show that the manganese(IV) oxide is not used up in the decomposition of hydrogen peroxide and that it still functions as a catalyst. 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(Total for Question 6 = 13 marks) 23 Turn over BLANK PAGE