Chemistry 12 HL
Option E
E10 Smog
Past Paper Questions
May 2008 TZ1
D4.
A constituent of photochemical smog is formed when the primary pollutant nitrogen monoxide
leads to the formation of an aldehyde secondary pollutant.
One possible sequence of reactions is described below.
• HO2• radicals in the atmosphere react with nitrogen monoxide to form hydroxyl radicals, HO•.
• Hydroxyl radicals convert hydrocarbon molecules (RCH3) to hydrocarbon radicals .
• Hydrocarbon radicals are oxidized by atmospheric oxygen to peroxyl radicals (RCH2O2 ).
• Peroxyl radicals convert nitrogen monoxide to nitrogen dioxide .
• The RCH2O radicals formed in reaction four react with atmospheric oxygen to form an aldehyde
and regenerate the HO2• radical .
Deduce an equation for each reaction in this sequence. [5]
November 2009
E3. The concentration of some pollutants in a city was measured over a 24 hour period. The results
are shown below.
(a) Outline the cause of the increase in NO levels between 5 and 8 am. [2]
Chemistry 12 HL
Option E
(b) Outline the cause of the increase in concentration of peroxyacylnitrates (PANs) between 8 am
and 2 pm. [2]
(c) State why a temperature inversion often results in the formation of smog. [1]
(d) Show, by stating an equation, how one of the above pollutants reacts with HO• radicals
to produce a constituent of acid rain. [1]
May 2010 TZ2
E4.
(a) Describe the atmospheric and geographical conditions that favour the formation of
photochemical smog. [3]
(b) Peroxyacylnitrates (PANs) are common secondary pollutants in photochemical smog.
Write a chemical equation for the formation of a PAN. [1]
November 2013
21.
a) The layer of ozone in the stratosphere, which plays an important role in helping to
protect the Earth’s surface from harmful radiation, is both formed and depleted by natural
processes. State chemical equations that show the natural depletion of ozone, including
the condition. [2]
b) The ozone layer has also been depleted by certain pollutants that have been released into
the atmosphere. State examples of two such ozone-depleting substances. [1]
Chemistry 12 HL
Option E
c) At ground level, ozone is a secondary pollutant present in photochemical smog.
(i) Using equations, outline the formation of ozone in smog starting from nitrogen(II) oxide. [3]
(ii) Describe any two geographical features or meteorological conditions that cause
ozone levels to rise. [1]
Unknown Origin
1.
(a) Identify two primary pollutants in photochemical smog and explain how one of these
pollutants is produced. [2]
(b) Identify two secondary pollutants in photochemical smog other than NO2 and O3. Explain with
the help of an equation how one of these pollutants is produced. [3]
(c) Explain how the formation of thermal inversions may increase the effect of pollution.
[2]