dreiprotonigen
Dreiprotonigen, or triprotic species, are chemical compounds that can undergo up to three successive proton transfer steps in aqueous solution. In acid–base chemistry a triprotic acid can lose three protons in a stepwise process: H3A ⇌ H2A− + H+, H2A− ⇌ HA2− + H+, and HA2− ⇌ A3− + H+. Each step has its own equilibrium constant, reflected in three dissociation constants (pKa1, pKa2, pKa3). The distribution of protonation states depends on pH and can be described by fractional concentrations (often denoted α0 to α3).
Common examples include inorganic acids such as phosphoric acid H3PO4, which has pKa values around 2.15, 7.20,
Applications and significance: triprotic acids are important in chemistry, biology, and environmental science because they provide
Notes: not all molecules with three hydrogens act as triprotic acids in solution. For example, boric acid