oxoacids

Oxoacids are a class of acids that contain hydrogen, oxygen, and at least one other element. They are the protonated forms of oxoanions; in aqueous solution, they can donate protons from oxygen atoms and form the corresponding oxoanions as conjugate bases, such as ClO4−, SO4^2−, or CO3^2−.

Common oxoacids include chloric acid (HClO3), chlorous acid (HClO2), and perchloric acid (HClO4); sulfuric acid (H2SO4) and sulfurous acid (H2SO3); nitric acid (HNO3) and nitrous acid (HNO2); phosphoric acid (H3PO4); and carbonic acid (H2CO3). Some heavier elements form oxoacids such as orthosilicic acid (H4SiO4).

Oxidation-state and oxygen count: more highly oxidized central atoms and more oxygens generally increase acidity, due to greater stabilization of the conjugate base by resonance and inductive effects. Many oxoacids are polyprotic, with multiple acidic hydrogens that dissociate stepwise; for example H2SO4 is diprotic, H3PO4 is triprotic, and HNO3 is monoprotic.

Importance and contexts: Oxoacids are central in inorganic chemistry, environmental chemistry (acid rain from sulfuric and nitric acids), biology and industry (fertilizers, etching, oxidizing agents). The conjugate bases are oxoanions, which participate in acid-base and redox reactions and often determine water chemistry in lakes and soils.