O-LevelChemistryChemistry of the Environment5070/21 · May/June 2019 · Q48 Marks

Air is a source of many gases.

(a)What is the percentage by volume of nitrogen in dry air?[1]
(b)Outline the separation of oxygen, nitrogen and the noble gases from liquid air.[3]
(c)State one large scale use of nitrogen.[1]
(d)(i)Air contains gaseous pollutants. Name one gas that contributes to acid rain.[1]
(d)(ii)State one environmental consequence of an increase in the percentage of carbon dioxide in the air.[1]
(d)(iii)Describe the source of carbon monoxide in air.[1]

Mark scheme

Marking points from the official mark scheme (May/June 2019). The mark or mark type is shown in brackets.

[1] 78%
[3] Any three from: fractional distillation (1)
[3] (liquid) air heated / (liquid) air vapourised (1)
[3] idea that different components have different boiling points (1)
[3] (gases with) lowest boiling point come off at the top / highest boiling point at the bottom / gases come off at different levels (in the column) (1)
[1] used to make fertilisers / used to make ammonia (1)
[1] sulfur dioxide / nitrogen dioxide (1)
[1] global warming / ice-caps melting / sea-level rising (1)
[1] incomplete combustion of carbon (-containing compounds) / incomplete combustion of hydrocarbons (1)

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