Hydrogen phosphate or monohydrogen phosphate (systematic name) is the inorganic ion with the formula [HPO<sub>4</sub>]<sup>2-</sup>. Its formula can also be written as [PO<sub>3</sub>(OH)]<sup>2-</sup>. 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 [PO<sub>4</sub>]<sup>3-</sup> and a conjugate base of dihydrogen phosphate [H<sub>2</sub>PO<sub>4</sub>]<sup>âÂÂ</sup>.
It is formed when a pyrophosphate anion reacts with water by hydrolysis, which can give hydrogenphosphate:
Hydrogenphosphate is an intermediate in the multistep conversion of phosphoric acid to phosphate: