Carbon dioxide is
present as a minor gas
in the atmosphere
(0.038%). The reaction
of carbon dioxide with
water forms
carbonic acid. CO2(aq) + H2O(aq) ® H2CO3(aq)
• Carbonic acid H2CO3 is the most
important naturally occurring
acid. (this hydroxide is a weak
acid) H2CO3(aq) D HCO3-(aq) + H+(aq)
• The exogenic cycle treats
the crust of the Earth as a large
acid-base titration system.
Carbonic acid in rain
water dissolves the basic
rocks which are carried away to oceans.
The components form sediments which are
then compressed back into rocks.