When carbon dioxide ``dissolves'' in water, essentially all of it reacts to form carbonic acid, H2CO3:
CO2(g)+H2O(l)⟷H2CO3(aq).
The carbonic acid can then dissociate into H+ and bicarbonate ions,
H2CO3(aq)⟷H+(aq)+HCO3−(aq).
(The table at the back of this book gives thermodynamic data for both of these reactions.) Consider a body of otherwise pure water (or perhaps a raindrop) that is in equilibrium with the atmosphere near sea level, where the partial pressure of carbon dioxide is 3.4×10−4 bar (or 340 parts per million). Calculate the molality of carbonic acid and of bicarbonate ions in the water, and determine the pH of the solution. Note that even ``natural'' precipitation is somewhat acidic.