Phosphoric acid, also termed orthophosphoric acid, is a substance with the chemical formula H₃PO₄. At high concentrations in aqueous solution, it is a relatively weak acid. The pH value at which a one molar solution exists as half orthophosphoric acid and half dihydrogen phosphate ion, H₂PO₄^-, the pK₁, is 2.15. At a pH of 7.20, the pK₂ a one molar solution of phosphoric acid exists as equal concentrations of dihydrogen phosphate ion and monohydrogen phosphate ion, H₂PO₄^2- and at pH 12.37, the pK₃ the solution consists of equal concentrations of monohydrogen phosphate and phosphate ion, PO₄^3-. At lower concentrations, a greater proportion of deprotonation occurs. Salts of all three anions can be prepared by using solutions of appropriate pH. Phosphoric acid is not an oxidizing acid: the phosphorus atom in the phosphate ion is fully oxidized.

Orthophosphoric acid is produced in quantities of...