12 (2410U20-1) 12 8. Compound A contains only carbon, hydrogen and an unknown halogen. Refluxing compound A in aqueous sodium hydroxide followed by the addition of nitric acid and aqueous silver nitrate produces a white precipitate. Elemental analysis of compound A indicates it contains 39.02% carbon and 3.25% hydrogen by mass. When bromine is added to compound A, 123 g of compound A reacts with 320 g of bromine. The 1H NMR spectrum of compound A consists of only one peak. The 13C NMR spectrum of compound A consists of two peaks. The infrared spectrum and simplified mass spectrum are shown below and overpage. 2000 1000 3000 0.6 0.7 0.8 0.9 1 Infrared spectrum Wavenumber (cm-1) Relative transmittance © WJEC CBAC Ltd. (2410U20-1) Turn over. 13 13 Examiner only 50 40 60 70 80 90 m/z 52 87 122 Relative intensity 100 110 120 130 140 150 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 Mass spectrum Use all of the data provided to determine the identity of compound A. Explain your answer using information from all of the data sources provided. [10] © WJEC CBAC Ltd. 2410 U201 13 14 (2410U20-1) 14 Examiner only © WJEC CBAC Ltd. 10 (2410U20-1) Turn over. 15 15 © WJEC CBAC Ltd. BLANK PAGE PLEASE DO NOT WRITE ON THIS PAGE 16 (2410U20-1) 16 Examiner only 9. Chloe was investigating the effect of using catalysts on the rate of reaction. She added 50 cm3 of 0.1 mol dm–3 iron(III) nitrate solution to 50 cm3 of 0.2 mol dm–3 sodium thiosulfate solution. The reaction forms a deep violet iron(III) complex which is unstable and is gradually reduced to form a light green iron(II) complex. Chloe monitored the rate of reaction by measuring the absorption of light at a wavelength of 500 nm every 10 seconds for two minutes using a data logger. (a) The violet complex appears black at the beginning of the reaction. State the name of the technique used to monitor the rate of reaction by measuring the absorption of light. [1] (b) Chloe repeated the experiment three times adding 1 cm3 of a different catalyst each time at a concentration 0.10 mol dm–3. Below is a graph showing her results: 0 0.2 0.4 0.6 0.1 0.3 0.5 0.7 0 20 40 60 Time / s Absorbance / arbitrary units 80 100 120 10 30 50 70 90 110 Key: No catalyst Co2+ Fe2+ Cu2+ (i) State which catalyst is the most effective. Explain your answer. [2] © WJEC CBAC Ltd. (2410U20-1) Turn over. 17 17 Examiner only (ii) Calculate the initial rate of reaction for the reaction catalysed by the copper(II) ions. [2] rate = ........................................................ s–1 (iii) Each catalysed reaction contained the same number of moles of catalyst at the beginning of the reaction. Calculate the moles of catalyst left at the end of the reaction. [1] moles = ........................................................ mol © WJEC CBAC Ltd. 18 (2410U20-1) 18 Examiner only (c) Increasing temperature and the addition of a catalyst are two ways of increasing the rate of a reaction. Using your knowledge of the Boltzmann distribution and particle theory, explain how the rate of reaction is increased using these two different methods. You may use a diagram(s) to support your answer. [6 QER] © WJEC CBAC Ltd. 12 (2410U20-1) Turn over. 19 19 © WJEC CBAC Ltd. BLANK PAGE PLEASE DO NOT WRITE ON THIS PAGE