Monohydrogen phosphate

Hydrogen phosphate or monohydrogen phosphate (systematic name) is the inorganic ion with the formula [HPO4]2-. Its formula can also be written as [PO3(OH)]2-. Together with dihydrogen phosphate, hydrogenphosphate occurs widely in natural systems. Their salts are used in fertilizers and in cooking. Most hydrogenphosphate salts are colorless, water soluble, and nontoxic.

It is a conjugate acid of phosphate [PO4]3- and a conjugate base of dihydrogen phosphate [H2PO4]−.

It is formed when a pyrophosphate anion reacts with water  by hydrolysis, which can give hydrogenphosphate:
 * + H2O 2

Acid-base equilibria
Hydrogenphosphate is an intermediate in the multistep conversion of phosphoric acid to phosphate:

Examples

 * Diammonium phosphate, (NH4)2HPO4
 * Disodium phosphate, Na2HPO4, with varying amounts of water of hydration