O-LevelChemistryChemistry of the Environment5070/21 · May/June 2023 · Q98 Marks

Oxides of nitrogen such as nitrogen monoxide, NO, are atmospheric pollutants. The exhaust gas from a car engine contains 0.00200% by volume of nitrogen monoxide.

(a)Calculate the number of molecules of nitrogen monoxide in 960dm³ of exhaust gas at room temperature and pressure. One mole of any gas contains 6.02 × 1023 molecules. number of molecules[3]
(b)Nitrogen and oxygen react to make nitrogen monoxide inside a car engine. Construct the equation for this reaction.[1]
(c)State one adverse effect of oxides of nitrogen as pollutants in the air.[1]
(d)Describe how oxides of nitrogen formed in a car engine are removed by a catalytic converter.[1]
(e)(i)The rate of diffusion of nitrogen dioxide, NO2(g), is less than that of nitrogen monoxide, NO(g), under the same conditions of temperature and pressure. Explain why the rate of diffusion of NO2(g) is less than that of NO(g) under the same conditions.[1]
(e)(ii)The rate of diffusion of nitrogen monoxide decreases as the temperature decreases. Suggest why using ideas about kinetic particle theory.[1]

Mark scheme

Marking points from the official mark scheme (May/June 2023). The mark or mark type is shown in brackets.

9(a) volume of NO = (0.002 × 960) ÷ 100 OR 0.0192 (1) moles of NO = (0.0192 ÷ 24) OR 0.0008 (1) number of molecules = 0.0008 × 6.02 × 1023 = 4.816 × 1020 (1)
9(b) N2 + O2 → 2NO (1)
9(c) acid rain / photochemical smog / respiratory problems (1)
9(d) reacted with CO to make nitrogen (1)
9(e)(i) NO2 has a higher (relative) molecular mass / molecule has more mass (1)
9(e)(ii) (NO) molecules move slower / (NO) molecules have less kinetic energy (1)

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