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Chemistry
for Secondary Schools
Preventing formation of acid rain
When the pH of rainwater falls below 5.6, it is called acid rain. Acid rain is
caused by chemical reactions between rainwater and gases such as sulfur dioxide
and nitrogen dioxide which are released into the atmosphere. Acid rain increases
the acidity of soils, rivers and lakes and adversely affects vegetation and aquatic
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organisms. To reduce this problem, air pollution devices containing bases are
fitted in exhaust pipes and chimneys to neutralise the acidic compounds before
reaching the atmosphere.
Neutralising accidental spills
If an acid or an alkali spills on the floor or work surface in the laboratory, it
can be neutralised. For example, sulfuric acid which is very corrosive, can be
neutralised by adding sodium hydroxide.
Manufacturing fertilisers
The production of ammonium fertilisers is done through the neutralisation of
ammonia with a mineral acid. Ammonium nitrate for example, is produced by the
reaction of ammonia with nitric acid.
Ammonia gas also reacts with sulfuric acid to give ammonium sulfate (NH 4 ) 2 SO 4
fertiliser (Figure 5.11).
Figure 5.11: Sack of ammonium sulfate fertiliser
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