Edexcel Jan 2015 (IAL) Paper 2 Q19

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SECTION B Answer ALL the questions. Write your answers in the spaces provided. 19 This is a question about catalysis. A spectacular demonstration of catalytic oxidation is the addition of chromium(III) oxide to ammonia gas in the presence of oxygen. This produces flashes, sometimes described as fireflies. Some concentrated ammonia solution is allowed to vaporise in a very large flask. Heated chromium(III) oxide catalyst is added. The equation below shows one possible reaction. 4NH3(g) + 5O2(g) (cid:111) 4NO(g) + 6H2O(g) (a) The nitrogen atoms in ammonia are oxidized. Give the oxidation numbers of the nitrogen atoms in ammonia and nitrogen monoxide. NH3 NO (b) Nitrogen monoxide is an example of a free radical. (i) Explain why nitrogen monoxide is classed as a free radical. (2) (1)(ii) Draw the dot and cross diagram of nitrogen monoxide, using dots ((cid:404)) for the nitrogen electrons and crosses () for the oxygen electrons. Show outer shell electrons only. (2) (c) Suggest one suitable safety precaution for this demonstration. Justify your choice. You can assume that the demonstrator is wearing a lab coat and safety goggles. (2)*P45042A01124* 11 Turn over<br /> (d) (i) Draw a Maxwell-Boltzmann diagram on the axes below, labelling the activation energy of the reaction and the vertical axis.*(ii) Use your diagram to explain how the presence of a catalyst such as chromium(III) oxide affects the rate of a chemical reaction. Kinetic energy, E (2) (2)(e) Suggest how solid catalysts work in gaseous reactions. (2)12 *P45042A01224*<br /> (f) The chromium(III) oxide catalyst can be produced from a remarkable demonstration commonly called the dichromate volcano. One experimental apparatus that could be used is shown below. silica gel granules loosely packed glass wool or mineral wool 1 dm3 conical flask ammonium dichromate(VI) heat to start the reaction (i) The substance used is ammonium dichromate(VI). Give the formula of ammonium dichromate(VI). (ii) This thermal decomposition reaction is also a redox reaction involving the oxidation of nitrogen atoms. However, it does not require oxygen gas. Suggest how the procedure could be modified to confirm that oxygen gas is not necessary for this oxidation. (1) (1)(iii) From your knowledge of other dichromate(VI) compounds, suggest the colour change that is observed in this demonstration. (1)(Total for Question 19 = 16 marks) *P45042A01324* 13 Turn over<br />

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