Phosphoric acid

Phosphoric acid, H3PO₄, also called orthophosphoric acid or white phosphoric acid, is the most common of the phosphoric acids and is one the six strong acids. It can be produced from the hydrolysis of its acid anhydride phosphorus(V) oxide, P₄O₁₀, also called tetraphosphorus decoxide. Organic polyphosphates serve as energy reserviors in living systems. It is severly corrosive and will cause burns on contact. In addition, it is incompatible with a wide variety of compounds with which it reacts in a very exothermic or even explosive fashion. Dangerous phosphorus oxides may be produced upon heating and decomposition.

physical properties

Phosphoric acid is a clear, colorless, odorless syrupy liquid that is miscible in all proportions with water, with a melting temperature of 21C and a boiling point of 158C. Phosphoric acid is a triprotic acid, in that all three protons can be dissociated. However, the third proton is not very acidic. The chemical formula can also be written as (HO)₃P=O, which more clearly indicates that each of the protons is bound to an oxygen atom.

H₃PO₄ <--> H⁺ + H₂PO₄^-      K₁ = 7.5 x 10^-3

H₂PO₄^- <--> H⁺ + HPO₄^2-      K₂ = 6.2 x 10^-8

HPO₄^2- <--> H⁺ + PO₄^3-      K₃ = 3.6 x 10^-13

Although salts can be produced incorporating each of the three anions, those formed with dihydrogen phosphate and hydrogen phosphate decompose upon heating, producing a metal trimetaphosphate (M_{3</su>(PO3)3 and water.}