CAIE A Level Chemistry 9701 · Nitrogen and sulfur
Nitrogen gas () is relatively unreactive, yet oxides of nitrogen such as and are formed in internal combustion engines and contribute to environmental problems.
Explain:
(a) how and are formed in internal combustion engines, with reference to the bonding in ;
(b) how acts both directly and catalytically in the formation of acid rain;
(c) how catalytic converters remove oxides of nitrogen from exhaust gases.
4 marks, so the mark scheme is looking for about 4 separate creditworthy points. Making the same point twice in different words earns it once.
Explain means: Give the reasons or the mechanism: why or how something happens. Link each point to the next with because, so or which means. A list of facts with no links usually loses the reasoning marks.
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