Clean Air – Revision Pack (C1)
What’s in ‘Clean Air’?
Gas
Composition in clean air
Nitrogen
78%
Oxygen
21%
Carbon Dioxide
0.035%
Other
<1%
These percentages change very little because the processes by which carbon
dioxide and oxygen are used up and made are fairly balanced.
For example:
-
In combustion, oxygen is used up and carbon dioxide is made
In the respiration of plants and animals, oxygen is used up and carbon
dioxide is made
In photosynthesis, carbon dioxide is used up and oxygen is made
This is the basis of the carbon cycle, and allows the amount of O 2 and CO 2 in the air
to be kept steady.
Over the last few hundred years, there has been a slight increase in the composition
of carbon dioxide in the air; this is for two main reasons:
-
Deforestation – less photosynthesis can take place
Population Increase – as population increases, the world’s energy
requirements increase as well
The Atmosphere:
The original atmosphere (envelope of gases) of Earth was formed when gases
escaped from inside the Earth. Plants that could photosynthesise back then,
removed carbon dioxide and added oxygen until the amount of oxygen in the
atmosphere reached its current 21% level.
When volcanoes ‘degas’ they release gases from the centre of the earth. The
compositions of this gas is often analysed by scientists, who can then form theories
about the original atmosphere.
One such theory says this:
-
The original atmosphere was rich in water vapour and carbon dioxide
The vapour condensed (changed into a liquid) and formed oceans
The carbon dioxide dissolved in the water
The composition of nitrogen increased slowly, but being unreactive wasn’t
removed from the atmosphere
Organisms that could photosynthesise converted the carbon dioxide and
water into oxygen
As the amount of oxygen in the air increased, the amount of carbon dioxide
slowly decreased until the current levels were reached
Clean Air – Revision Pack (C1)
Pollution Control:
It is important that we control pollution because of the effects it can have on:
-
People’s health (e.g. asthma)
The natural environment (e.g. atmosphere
The built environment (e.g. buildings)
Sulphur dioxide (SO 2 ) is a pollutant that can cause breathing difficulties in those with
asthma; it can also damage wildlife and limestone (CaCO 3 ).
A car is fitted with a catalytic converter which changes CO (a pollutant) into CO 2 .
The catalyst is made of platinum and rubidium and has a large surface area. The
temperature needs to be very high, which it is in a car engine. The reaction is
between carbon monoxide (CO) and nitric monoxide (NO) which are both
pollutants formed by petrol and diesel fuelled cars. The reaction in the catalytic
converter makes two natural components, and much less dangerous gases. The
balanced symbol equation for this is:
2CO + 2NO  N 2 + 2CO 2
An oxide of nitrogen (NO) is a photochemical smog acid rain formed by nitrogen
and oxygen at a very high temperature.
When nitric monoxide (NO) is released into the air it forms with oxygen to make nitric
dioxide which caused acid rain.
Clean Air – Revision Pack (C1)
Past Papers:
PPQ(1):
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Mark Schemes:
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PPQ(5):