Carbonic acid is a chemical compound with the chemical formula H2CO3 and is also a name sometimes given to solutions of carbon dioxide in water (carbonated water), because such solutions contain small amounts of H2CO3(aq). Carbonic acid, which is a weak acid, forms two kinds of salts: the carbonates and the bicarbonates.
In geology, carbonic acid causes limestone to dissolve, producing calcium bicarbonate—which leads to many limestone features such as stalactites and stalagmites. Carbonic acid is a polyprotic acid, specifically it is diprotic, meaning that it has two protons which may dissociate from the parent molecule.
When carbon dioxide dissolves in water, it exists in chemical equilibrium, producing carbonic acid:
The reaction can be pushed to favor the reactants to generate CO2(g)CO2(g) from solution, which is key to the bubbles observed in carbonated beverages