Acid Rain
Introduction
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Acid rain as the name suggests is rain that is acidic, the term is
used to describe rain with a pH below 5, before the industrial
revolution rain had a typical pH of 5 to 6 this was before the
increase in air pollution brought about by the burning of fossil
fuels, that are burned in factories, vehicles and power stations.
The term “acid rain” was first used over a hundred years ago by the
British chemist Robert Angus Smith. When he realized that the smoke
from human activity could change the acidity of precipitation, despite
this it was not until the 1950’s that concern was raised about the
environmental effect and even then this situation was allowed to
continue to rise until it reached crisis proportions in the late
1970’s
The only forms of air pollution were caused by geological events for
example volcano eruptions, lightning and bacterial action in soils
etc.
The increase of certain gasses in the air, sulphur dioxide, carbon
dioxide, methane, halocarbons and nitrogen oxides being the main ones,
leads to them being absorbed into it the water vapour that is present
in the atmosphere at high altitudes this reaction is increased by the
energy from sun light, As the sulphur dioxide and nitrogen oxides
react with the water vapour, oxygen and other oxidants a mild solution
of sulphuric acid and nitric acid are formed. This weak acid vapour
can now precipitate into clouds and fall as acid rain, acid snow and
even acidic fog.
Global warming is another problem that
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Chemistry of acid rain
.rainwater is slightly acidic.
Co2+H2OàH2CO3
H2CO3àH++HCO3
Carbon dioxide can dissolve in water, some of which forms carbonic
acid. Carbonic acid releases H+ making the water slightly acidic.
.Burning sulphur releases SO2.
2S+O2à2SO2
Sulphur in coal released as sulphur dioxide.
.sulphur dioxide acidifies water slightly.
SO2+H2OàH2SO3
H2SO3àH++HSO3
Sulphur dioxide can dissolve in water, some of which forms sulphurous