veelprotonische

Veelprotonische refers to acids that can donate more than one proton in acid-base reactions. In English, the equivalent term is polyprotic (or polyprotonic) acids. These acids contain several ionizable hydrogens and undergo a series of successive dissociations in aqueous solution, each with its own dissociation constant (Ka1, Ka2, Ka3, …). The general steps can be written as H2A ⇌ H+ + HA−; HA− ⇌ H+ + A2−; HA2− ⇌ H+ + A3−. The magnitudes of the successive pKa values determine the pH ranges over which each proton is released; if the pKa values are well separated, the molecule behaves like a monoprotic acid over broad pH intervals, with distinct buffering around each pKa.

Common examples include sulfuric acid (H2SO4), a diprotic acid with a very strong first dissociation and a weaker second; carbonic acid (H2CO3), also diprotic; and phosphoric acid (H3PO4), a triprotic acid with three dissociation steps. For H3PO4 the pKa values are approximately 2.1, 7.2, and 12.3. The concept of polyprotic acidity is important for understanding buffering capacity, acid-base titrations, and the role of acids in biogeochemical and biochemical systems.

In Dutch-language chemistry, veelprotonische zuren are the standard term for what English texts call polyprotic acids, underscoring the focus on multiple protons released in discrete steps.