Question

Cleary explain how the bufferH2CO3 neutralizes an acid that is added to a solution that contains it.
And, if the pH of the solution was 7.0 before the acid was added, what would it be after the acid was added

Answer 1

The chemical reaction

CO2 + H2O -> H2CO3; carbonic anhydrase is used to catalyze this reaction.
H2CO3 can be dissociated into hydrogen ions and bicarbonate ion
H2CO3 -> H+ + HCO3-

These reactions are reversible.
Acid in the solution will produce H+ ions. Because of Lechatelier's Principle H+ ions in excess will rapidly combine with the bicarbonate ions to produce carbonic acid, and the pH of the solution will be back to normal. In addition, H2CO3 in excess will rapidly dissociate into carbon dioxide and H2O.

Normally, acid is responsible to decrease the pH of the solution. In this case, pH is maintained at a normal level because H+ ions (added by an acid) can combine with bicarbonate ions to form Carbonic acid.