bicarbonate ion carbonic acid A buffer minimize changes in pH by accepting hydrogen ions from the solution when they are in excess and donating hydrogen ions to the solution when they are low.

In human blood, dissolved CO2 forms Carbonic acid (H2CO3).

Carbonic acid acts as a buffer by dissociating to yield a bicarbonate ion (HCO3-) and a hydrogen ion (H+) in a dynamic equilibrium.