O-LevelChemistryChemistry of the Environment5070/22 · May/June 2021 · Q610 Marks

Sulfur dioxide and oxides of nitrogen are pollutants found in air.

(a)State one environmental problem caused by the presence of sulfur dioxide in the air.[1]
(b)Coal-fired power stations produce sulfur dioxide as a pollutant. The sulfur dioxide produced is prevented from entering the air by a process called flue gas desulfurisation, FGD. Name the compound used in FGD that reacts with the sulfur dioxide.[1]
(c)(i)Construct the equation for this reaction.[1]
(c)(ii)Draw a dot-and-cross diagram to show the bonding in a molecule of nitrogen. Only include the outer shell electrons.[1]
(c)(iii)Explain why the rate of reaction between nitrogen and oxygen increases as the temperature increases.[2]
(d)(i)Nitrogen dioxide reacts with aqueous sodium hydroxide to form two different salts and water. Construct the equation for this reaction.[2]
(d)(ii)Nitric acid is a strong acid. Nitrous acid is a weak acid. Describe the difference between a weak acid and a strong acid.[2]

Mark scheme

Marking points from the official mark scheme (May/June 2021). The mark or mark type is shown in brackets.

[1] acid rain
[1] calcium carbonate
[1] N₂ + O₂ → 2NO
[1] X N triple bond N X / 3 shared pairs (1) / 1 lone pair on each N (1)
[1] particles move faster / particles have more kinetic energy (1)
[1] more successful collisions / more (particles) have energy above the activation energy / more effective collisions (1)
[1] 2NO₂ + 2NaOH → NaNO₂ + NaNO₃ + H₂O (1)
[1] formula for NaNO₂ (1)
[1] balancing (1)
[1] strong acid completely dissociates / completely ionises (1)
[1] weak acid incompletely dissociates / incompletely ionises / partially dissociates / partially ionises (1)

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