A-LevelChemistryNitrogen and sulfur9701/22 · May/June 2017 · Q213 Marks

Nitrogen gas, N₂, is very unreactive.

(a)Explain why nitrogen gas is so unreactive.[2]
(b)(i)Explain why oxides of nitrogen can be produced by internal combustion engines.[2]
(b)(ii)State and explain, using a suitable equation, how oxides of nitrogen produced by internal combustion engines can be prevented from reaching the atmosphere.[2]
(b)(iii)State the role of nitrogen dioxide, NO₂, in the formation of acid rain by oxides of sulfur. Write suitable equations to explain this role. role equation 1 equation 2[3]
(b)(iv)Suggest an equation to show how NO₂ can contribute directly to acid rain.[1]
(c)Explain how the uncontrolled use of nitrate fertilisers on land can lead to a severe reduction in water quality in rivers.[3]

Mark scheme

Marking points from the official mark scheme (May/June 2017). The mark or mark type is shown in brackets.

[1] strong triple bond
[1] non-polar / no dipole
[1] nitrogen (and oxygen) from the air / atmosphere (react)
[1] high temperature (of internal combustion engine) / (engine) produces enough OR a lot of heat (energy)
[1] (so) breaks (strong) bond(s) in nitrogen (and oxygen)
[1] reduction / decomposition of NOx using a catalyst / catalytic convertor
[1] 2NO2 + 4CO → 4CO2 + N2 OR 2NO + 2CO → 2CO2 + N2
[1] (acts as a homogeneous) catalyst OR oxidising agent
[1] SO2 + NO2 → SO3 + NO
[1] NO + 1/2O2 → NO2 OR SO3 + H2O → H2SO4
[1] 2NO2 + H2O → HNO2 + HNO3 OR 4NO2 + 2H2O + O2 → 4HNO3
[1] fertiliser/nitrates dissolve in (river water) OR fertiliser/nitrates are washed / leached out / flows into (river water)
[1] algal bloom / promote algal growth / explosion of plant growth
[1] drop in oxygen (concentration)

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