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.
-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 O2 and CO2 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 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
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 (SO2) is a pollutant that can cause breathing difficulties in those with asthma; it can also damage wildlife and limestone (CaCO3).
A car is fitted with a catalytic converter which changes CO (a pollutant) into CO2.
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 N2 + 2CO2
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.
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