Edexcel Jan 2012 Paper 2 Q22

Answers available below

PMT SECTION C Answer ALL the questions. Write your answers in the spaces provided. 22 Nitrogen monoxide is an unusual molecule both in its chemical structure (shown below) and in its impact on our lives. N O Nitrogen monoxide is an important chemical messenger in all mammals and, at appropriate concentrations, it is vital to life; however, at high concentrations in the body, it is extremely toxic. Nitrogen monoxide is considered a dangerous atmospheric pollutant; it is involved in the formation of a range of toxic substances, including ozone, at low altitudes, and in the depletion of the ozone layer at high altitudes. Nitrogen monoxide is formed by the direct combination of nitrogen and oxygen at high temperatures, a reaction that occurs naturally in lightning discharges, and as a by- product of the reactions in internal combustion and jet engines. Catalytic converters reduce nitrogen monoxide emissions from car engines by catalysing the reaction between nitrogen monoxide and carbon monoxide to form nitrogen and carbon dioxide. The reactions of nitrogen monoxide which involve ozone in the atmosphere are summarised below. 2NO(g) + O2(g) (cid:85) 2NO2(g) NO2(g) UV radiation NO(g) + O(g) O2(g) + O(g) NO(g) + O3(g) O3(g) NO2(g) + O2(g) When the ratio of nitrogen dioxide to nitrogen monoxide is high (> 3), the rate of formation of ozone is faster than its rate of removal. When the ratio is low (< 0.3), the reverse is true. Ozone causes breathing difficulties, headaches, fatigue and can aggravate respiratory problems. The reaction of nitrogen monoxide with hydrocarbons can also produce other toxic compounds, such as aldehydes. (a) Write the equation for the formation of nitrogen monoxide from nitrogen and oxygen. State symbols are not required. (1) 18 *P39303A01824*<br /> (b) The electronic structure of nitrogen monoxide is unusual in that it has an unpaired electron. PMT (i) What name is given to a chemical species such as nitrogen monoxide that has an unpaired electron? (1)(ii) Chemical species with unpaired electrons occur as intermediates in some chemical reactions. What type of bond breaking produces these species? (1)(c) (i) Suggest the most likely source of the hydrocarbons that react with nitrogen monoxide to form toxic compounds. (1)(ii) Suggest the type of reaction that is involved when a hydrocarbon is converted into an aldehyde. (1)(iii) Draw the skeletal formula of the aldehyde with three carbon atoms. (1) (iv) By considering the equation NO(g) + O3(g) NO2(g) + O2(g) explain the effect of the reaction of hydrocarbons with nitrogen monoxide on the breakdown of ozone. (1)*P39303A01924* 19 Turn over<br /> PMT (d) Suggest why the proportion of nitrogen dioxide might be reduced at high altitudes. (2)(e) Explain why it is important to maintain the concentration of ozone in the upper atmosphere. (2)(f) (i) Write an equation for the reaction on a catalytic converter described in the passage. State symbols are not required. (1) 20 *P39303A02024*<br /> (ii) Draw an energy profile for the exothermic reaction in (f)(i). Label the axes, the reactants and products, the enthalpy change and the activation energy. (3) PMT *(iii) By referring to your energy profile, explain how a catalyst speeds up a chemical reaction. (3)(cid:3) (cid:11)(cid:74)(cid:12)(cid:3)(cid:45)(cid:72)(cid:87)(cid:3)(cid:68)(cid:76)(cid:85)(cid:70)(cid:85)(cid:68)(cid:73)(cid:87)(cid:3)(cid:68)(cid:85)(cid:72)(cid:3)(cid:70)(cid:82)(cid:81)(cid:86)(cid:76)(cid:71)(cid:72)(cid:85)(cid:72)(cid:71)(cid:3)(cid:68)(cid:3)(cid:74)(cid:85)(cid:72)(cid:68)(cid:87)(cid:72)(cid:85)(cid:3)(cid:87)(cid:75)(cid:85)(cid:72)(cid:68)(cid:87)(cid:3)(cid:87)(cid:82)(cid:3)(cid:87)(cid:75)(cid:72)(cid:3)(cid:82)(cid:93)(cid:82)(cid:81)(cid:72)(cid:3)(cid:79)(cid:68)(cid:92)(cid:72)(cid:85)(cid:3)(cid:87)(cid:75)(cid:68)(cid:81)(cid:3)(cid:85)(cid:82)(cid:68)(cid:71)(cid:3)(cid:89)(cid:72)(cid:75)(cid:76)(cid:70)(cid:79)(cid:72)(cid:86)(cid:17)(cid:3)(cid:3) Suggest an explanation for this. (2)(Total for Question 22 = 20 marks) TOTAL FOR SECTION C = 20 MARKS TOTAL FOR PAPER = 80 MARKS *P39303A02124* 21<br />

Show answer