Polyprotic acids have more than one hydrogen ion and are lost sequentially. Acids having two dissociable hydrogen ions that can be transferred in a reaction are diprotic while acids having three dissociable hydrogen ions are called triprotic. Phosphoric acid [local], H₃PO₄, is an example of a mineral acid that is triprotic, citric acid is a triprotic organic acid. In a solution of H₃PO₄ there is a distribution of the following species: H₃PO₄, H₂PO₄^-, HPO₄^2-, and PO₄^3-.

The amount of each can be determined using the relative fractions [local],the alpha ratio. Phosphoric acid has four species that can be present in solution at a given pH. The fraction of each species can be determined by calculation of the alpha ratio to the concentrations of all the other possibilities, and the alpha 1 is the ratio of [H₂PO₄^-] to [H₃PO₄]%2B[H₂PO₄^-]%2B[ HPO₃^2-]%2B[PO₄^3-] and so on for the alpha 2 and alpha 3. The formula for each alpha ratio is listed below:

Below is a chart that depicts the reaction of H₃PO₄ with NaOH.