HCO3jonen

HCO3−, commonly referred to as the bicarbonate ion, is a chemical anion with the formula HCO3−. It is the conjugate base of carbonic acid (H2CO3) and the conjugate acid of carbonate (CO3^2−). In aqueous solution, bicarbonate participates in the carbonate buffering system and exists in equilibrium with carbon dioxide and carbonic acid: CO2 + H2O ⇌ H2CO3 ⇌ HCO3− + H+. Its protonation state depends on pH, with pKa values around 6.35 for the H2CO3/HCO3− couple and around 10.3 for the HCO3−/CO3^2− couple. This makes bicarbonate amphiprotic, able to act as either a weak base or a weak acid depending on the environment.

In biology, bicarbonate is a central component of the body's acid-base balance. The blood uses the bicarbonate buffering system to maintain pH near 7.35–7.45, with levels regulated by the lungs (via CO2 exhalation) and kidneys (via reabsorption and excretion). Normal arterial bicarbonate concentration in humans is typically about 22–28 mEq/L.

In environmental chemistry, bicarbonate is a major inorganic carbon species in seawater and freshwater. It contributes to the carbonate buffering system that stabilizes pH and interacts with calcium and carbonate ions to influence mineral formation, including shells and skeletons in many organisms. Rising atmospheric CO2 shifts carbonic carbon into bicarbonate and carbonate species, affecting ocean chemistry.

Common salts include sodium bicarbonate (NaHCO3) and potassium bicarbonate (KHCO3), widely used in baking, food processing, medicine, and industry. Large excesses can disrupt acid-base balance and cause health issues.