Carbonic acid is the most common acid in naturally occurring water. It is a chemical compound with the formula H2CO3. It forms in small amounts when carbon dioxide gas (CO2) dissolves in water (H2O).
Carbonated beverages, which are fizzy with carbon dioxide bubbles, contain small amounts of carbonic acid. Carbonic acid in underground water slowly dissolves limestone rock, gradually forming caves. Within animal bodies, carbonic acid plays an important role in transporting carbon dioxide in the blood. This process helps remove carbon dioxide via the lungs and keeps the body from becoming too acidic.
The oceans absorb a great deal of carbon dioxide from the air to form carbonic acid. This process, called ocean acidification, can disrupt the health of corals and other ocean creatures. Human activity has greatly increased the amount of carbon dioxide in Earth’s atmosphere. This extra carbon dioxide, in addition to contributing to global warming, has also led to increased ocean acidification.
Like other acids, carbonic acid reacts with a base in a process called neutralization. The reaction can produce two kinds of salts. If only one hydrogen atom in carbonic acid reacts with a base, a bicarbonate salt forms. If both hydrogen atoms react with a base, a carbonate salt forms.
Many scientists once thought that carbonic acid could only exist in a solution of water. But pure carbonic acid can likely exist as a gas or solid at low temperatures, provided water is not present. Some scientists think carbonic acid may be present in clouds at high altitudes and in the tails of comets.
