Chemistry Reference
In-Depth Information
This sulfur dioxide gas dissolves in rainwater to form
the weak acid, sulfurous acid (H
2
SO
3
).
sulfur dioxide + water
sulfurous acid
SO
2
(
g
) + H
2
O(
l
)
H
2
SO
3
(
aq
)
A further reaction occurs in which the sulfurous
acid is oxidised to sulfuric acid. Solutions of these
acids are the principal contributors to acid rain. For
a further discussion of acid rain, see Chapter 12,
p. 198.
Units called fl ue gas desulfurisation (FGD) units
are being fi tted to some power stations throughout
the world to prevent the emission of sulfur dioxide
gas. Here, the sulfur dioxide gas is removed from
the waste gases by passing them through calcium
hydroxide slurry. This not only removes the sulfur
dioxide but also creates calcium sulfate, which can
be sold to produce plasterboard (Figure 11.25). The
FGD units are very expensive and therefore the sale
of the calcium sulfate is an important economic part
of the process.
Questions
1
Write a balanced chemical equation to represent the
reaction which takes place between sulfur dioxide and
calcium hydroxide slurry in the FGD unit of a power station.
2
It has been found that air pollution in cities damages lung
development in children. Use the information in the text
and any other information to make a list of the pollutants
responsible for this problem.
3
Write down one problem that can be caused by each of
these air pollutants:
a
nitrogen dioxide
b
particulates.
4
Is carbon dioxide an atmospheric pollutant? Give reasons
for your answer.
●
Water
Water is the commonest compound on this planet.
More than 70% of the Earth's surface is covered with
sea, and the land masses are dotted with rivers and
lakes (Figure 11.26a). It is vital to our existence and
survival because it is one of the main constituents in
all living organisms. For example, your bones contain
72% water, your kidneys are about 82% water and
your blood is about 90% water (Figure 11.26b).
Figure 11.25
This plasterboard is made using calcium sulfate from an
FGD plant.
a
Millions of tonnes of water pass over this waterfall every day.
Another source of pollution is hydrogen sulfi de (H
2
S),
a poisonous gas which has the distinctive smell of
rotten eggs. It is present in volcanic emissions. Crude
oil also contains small quantities of hydrogen sulfi de
and this is removed during its processing. Since the
introduction of catalytic converters, modern cars have
shown an increased tendency to produce H
2
S on
heavy acceleration. This can be improved by tuning
the engine. Where amounts of hydrogen sulfi de are
present in the air, it causes irritation to the lungs. It also
blackens lead-based paints.
b
Your blood contains a lot of water.
Figure 11.26
