Chemistry Reference
In-Depth Information
If farm crops are harvested from the land rather
than left to decay, the soil becomes defi cient in this
important element. The nitrogen is removed in the
harvested crops rather than remaining as the plants
decay. In addition, nitrates can be washed from the
soil by the action of rain (leaching). For the soil to
remain fertile for the next crop, the nitrates need to
be replaced. The natural process is by decay or by the
action of lightning on atmospheric nitrogen. Without
the decay, however, the latter process is not effi cient
enough to produce nitrates on the scale required.
Questions
1
Calculate the percentage of nitrogen in each of the four
fertilisers in Table 11.7. (
A
r
: H
=
1; N
=
14; O
=
16; P
=
31;
S
=
32)
2
Write down a method that you could carry out in a school
laboratory to prepare a sample of ammonium sulfate fertiliser.
3
Use your research skills to fi nd out about the process of
producing nitric acid by the oxidation of ammonia. Include
in your answer key chemical equations and also refer to the
major uses of this acid.
●
Atmospheric pollution
The two major resources considered in this chapter,
water and air, are essential to our way of life and
our very existence. Water and air make up the
environment of a living organism. The environment
is everything in the surroundings of an organism
that could possibly infl uence it. Humans continually
pollute these resources. We now look at the effects
of the various sources of pollution of the air and at
the methods used to control or eliminate them. For a
discussion of water pollution, see p. 190.
Air pollution is all around us. Concentrations of gases
in the atmosphere such as carbon monoxide, sulfur
dioxide and nitrogen oxides are increasing with the
increasing population. As the population rises there is
a consequent increase in the need for energy, industries
and motor vehicles. These gases are produced primarily
from the combustion of the fossil fuels coal, oil and gas,
but they are also produced by the smoking of cigarettes.
Motor vehicles are responsible for much of the air
pollution in large towns and cities. They produce
four particularly harmful pollutants:
●
carbon monoxide - toxic gas
●
sulfur dioxide - major irritant and constituent of
acid rain
●
hydrocarbons - carcinogenic
●
oxides of nitrogen - major irritant, acid rain and
photochemical smog
●
lead compounds - toxic.
Farmers often need to add substances containing
these nitrates. Such substances include farmyard
manure and artifi cial fertilisers. One of the most
commonly used artifi cial fertilisers is
ammonium
nitrate
, which as you saw earlier is made from
ammonia gas and nitric acid, both nitrogen-
containing compounds.
Problems with fertilisers
If artifi cial fertilisers of all kinds are not used
correctly, problems can arise. If too much fertiliser is
applied to the land, rain washes the fertiliser off the
land and into rivers and streams. This leaching leads
to
eutrophication
by encouraging the growth of algae
and marine plants. As the algae die and decay, oxygen
is removed from the water, leaving insuffi cient amounts
for fi sh and other organisms to survive (Figure 11.22).
In extreme cases, no normal aquatic life can survive.
There are also worries about the effect of agricultural
fertilisers, especially nitrates, on the public water supply.
There is evidence that the fertiliser sodium nitrate
is implicated in infant brain damage, and it is also
suspected of being carcinogenic.
Nitrogen monoxide is formed by the reaction of
nitrogen and oxygen inside the internal combustion
engine at high temperatures.
nitrogen + oxygen → nitrogen monoxide
N
2
(
g
)
+
O
2
(
g
) →
2NO(
g
)
The nitrogen monoxide, emitted as an exhaust
gas, reacts with oxygen from the air to form the
Figure 11.22
Over-use of fertilisers has led to eutrophication in this river.
Oxygen is removed from the water and organisms cannot survive.
