It is one of the major buffering systems used to maintain the pH of mammalian blood.
It is used in the formation of acid in the lumen on the stomach.
It is used to neutralize the pH of the chyme leaving the stomach and entering the small intestine.
Carbonic acid is known as a weak acid because it partially dissociates into the positive Hydrogen ions and negative bicarbonate ions.
All of the above reactions are reversible and subject to the laws of mass action.
For example, when excess hydrogen ions are added
to the system the equilibrium is shifted to the left. This means that some
of the added hydrogen ions will react with the bicarbonate ions to produce
carbonic acid and the carbonic acid will dissociate into carbon dioxide
and water as shown below.
When hydrogen ions are removed from the reaction, the equilibrium
will shift to the right. More carbon dioxide will combine with water and
more carbonic acid will be produced and more hydrogen ions and bicarbonate
ions will be produced.
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