The pka values of carbonic acid are 6.3 for carbonic (I) and 10.3 for carbonic (II). Carbonic (I) has the molecular formula of H2CO3 while carbonic (II) has the molecular formula of HCO3-.
Carbonic acid is a weak acid formed in solution when carbon dioxide is dissolved in water. In addition to being in equilibrium with carbon dioxide, it also dissociates into hydrogen carbonate and hydrogen ions. This is a process that takes place in red blood cells. Carbon dioxide leaves the tissues and diffuses into the cells. The reaction is catalyzed by an enzyme called carbonic anhydrase. Carbonic acid is responsible for the sharp taste in beverages.