Acid rain revision.

It might pay to start this topic with some revision of acids and bases.  I posted this one last year….

Rain containing dissolved carbon dioxide is acidic.

Rainwater is naturally acidic, with a pH around 5.6.  This is due to the fact that there are gases present in the atmosphere that undergo natural processes to react with water vapour and form acids.  For example, carbon dioxide can form carbonic acid.  The carbonic acid partially ionises to form a low concentration of H+ ions. The H+ ions are what makes the water acidic, and therefore lowers the pH.

CO2 + H2O –> H2CO3

H2CO3 –> H+ + HCO3

HCO3 –> H+ + CO32-

pH is a measure of the concentration of hydrogen ions: i.e. pH = – log [H+].

pH = -log[H3O+]

pOH = -log[OH]

[H3O+] = 10-pH

pH + pOH = 14

There are a few equations that you are just going to have to memorise. A few things to point out if you have forgotten…

  • The square brackets mean ‘concentration of’
  • H3O+ and H+ are both used interchangeably to represent an acid

And theres always the interacive animations that I have posted previously that you can check out…

For some more details on acid rain, its formation and its effects (you need to know about all of these) , check out the following sites:



Department of Chemistry, Washington



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