tribasic

Tribasic is a chemistry term used to describe a substance that can donate three protons in acid-base reactions, i.e., a triprotic acid. In water, such an acid with the formula H3A can progressively lose protons to form H2A−, HA2−, and A3−, governed by three successive dissociation constants: Ka1, Ka2, and Ka3. The values of these constants determine how the species distribute among protonation states across pH, and they define the buffering ranges of the acid.

Common tribasic acids include phosphoric acid (H3PO4) and citric acid (C6H8O7). Phosphoric acid has pKa values around 2.15, 7.20, and 12.35, corresponding to the loss of its three protons. Citric acid has pKa values approximately 3.13, 4.76, and 6.40, reflecting its three acidic sites. Other tribasic acids are encountered in organic and inorganic chemistry, particularly among polycarboxylic acids that present three distinct ionizable protons.

Applications of tribasic acids arise from their multiple buffering capacities and reactivity. They are used to prepare buffer solutions covering multiple pH ranges, in fertilizers and food processing, and in beverage formulation where controlled acidity and buffering are important. In analytical chemistry, triprotic acids enable titrations with multiple endpoints and more nuanced buffering behavior than monoprotic or diprotic systems.

In summary, tribasic refers to acids capable of donating three protons, characterized by three dissociation steps and three pKa values, which impart distinctive buffering properties and practical utility in chemistry and industry.