(2410U20-1) 14 14 © WJEC CBAC Ltd. 11. Compound X contains only carbon, hydrogen and oxygen. On analysis it was found to contain 53.3 % carbon and 11.1 % hydrogen by mass. A simplified form of the mass spectrum and the infrared absorption spectrum for X are shown. The low resolution 1H NMR spectrum of X has three peaks. When X is warmed with excess acidified potassium dichromate(VI) there is a colour change. The organic product of this reaction does not react with aqueous sodium carbonate. 0 10 20 30 40 50 60 70 80 90 Intensity m/z 2000 1000 3000 0.0 0.8 1.0 0.6 0.4 0.2 Transmittance Wavenumber (cm–1) (2410U20-1) 15 Turn over. 15 © WJEC CBAC Ltd. Examiner only (a) Use all the data given to find the structure of compound X. Explain what information can be found from each piece of data. [10] Structure of X Examiner only 16 (2410U20-1) 16 © WJEC CBAC Ltd. (b) (i) State the type of reaction that occurs when X is warmed with acidified potassium dichromate(VI). [1] ....................................................................................................................... (ii) Draw the structure of the organic product formed when X reacts with acidified potassium dichromate(VI). [1] 12 (2410U20-1) Turn over. 17 17 © WJEC CBAC Ltd. BLANK PAGE PLEASE DO NOT WRITE ON THIS PAGE 18 (2410U20-1) 18 © WJEC CBAC Ltd. Examiner only 12. (a) Iodide ions can be oxidised to iodine by reaction with acidified hydrogen peroxide. H2O2 I2 2I– + 2H2O + 2H+ + The rate of reaction can be followed in a clock reaction by the appearance of a blue-black colour. An experiment was carried out to determine the effect on the rate of reaction of varying the concentration of iodide ions. All other volumes and concentrations were kept constant. The results are shown in the table. Concentration I– / mol dm–3 Time for appearance of blue-black colour / s Rate / s–1 × 1000 0.1 56 18 0.2 20 .................................. 0.3 18 .................................. 0.4 12 .................................. 0.5 10 .................................. (i) Use rate = 1000 time to calculate the rate for each experiment and complete the table. [1] (2410U20-1) 19 19 © WJEC CBAC Ltd. Turn over. Examiner only (ii) On the axes below, plot the concentration of I– against rate and draw a suitable line. [3] (iii) From the graph deduce the relationship between concentration of I– and rate of reaction. [1] (iv) Use the graph to calculate the time the reaction would take to turn blue-black using a 0.15 mol dm–3 solution of I–. Show clearly how you obtained your answer. [2] Time = ....................................................... s (2410U20-1) 20 20 © WJEC CBAC Ltd. Examiner only (v) For each experiment the rate was calculated using the time taken to produce excess iodine. Explain why this is only an approximation for the rate as the reaction proceeds. [2] (b) (i) Draw a Boltzmann energy distribution curve. Label the axes. [2] (ii) Use this energy distribution curve to explain how catalysts affect the rate of a reaction. [2] 13 Turn over. (2410U20-1) 21 © WJEC CBAC Ltd. Examiner only 13. (a) Explain what is meant by a carbon-neutral fuel. [3] (b) Ethane and an unknown alkane were burned in oxygen. It follows from the equation below that one volume of ethane produced two volumes of carbon dioxide and three volumes of water vapour. C2H6(g) + 7 2 O2(g) 2CO2(g) + 3H2O(g) 10 cm3 of the unknown alkane CxHy burned according to the following equation. CxHy(g) + (x + y 4 )O2(g) xCO2(g) + y 2  H2O(g) The total volume of carbon dioxide and water vapour produced was 20 cm3 more than the original volume of CxHy and oxygen. All volumes were measured at the same temperature and pressure. (i) State the volumes of carbon dioxide and water vapour produced on burning 10 cm3 of the unknown alkane in terms of x and y. [1] Volume carbon dioxide = ....................................................... cm3 Volume water vapour = ....................................................... cm3 (ii) Calculate the value of y. [2] y = .......................................... END OF PAPER 6 21 (2410U20-1) 22 © WJEC CBAC Ltd. 22 BLANK PAGE PLEASE DO NOT WRITE ON THIS PAGE (2410U20-1) 23 © WJEC CBAC Ltd. 23 Examiner only Question number Additional page, if required. Write the question number(s) in the left-hand margin. (2410U20-1) 24 © WJEC CBAC Ltd. 24 BLANK PAGE PLEASE DO NOT WRITE ON THIS PAGE