Monohydrogen phosphate

Hydrogen phosphate
Names
	Preferred IUPAC name Hydrogenphosphate
	Systematic IUPAC name Monohydrogenphosphate; Phosphoric acid, ion(2-)
	Other names Phosphoric acid, ion(2-); Hydrophosphoric acid (2-); Biphosphate (2-)
Identifiers
CAS Number	14066-19-4;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:43474;
ChemSpider	2913859;
Gmelin Reference	1998
PubChem CID	3681305;
UNII	33UE6C4909;
CompTox Dashboard (EPA)	DTXSID10394962 ;
	InChI InChI=1S/H3O4P/c1-5(2,3)4/h(H3,1,2,3,4)/p-2 Key: NBIIXXVUZAFLBC-UHFFFAOYSA-L;
	SMILES OP(=O)([O-])[O-];
Properties
Chemical formula	HPO2−; 4
Conjugate acid	Dihydrogen phosphate
Conjugate base	Phosphate
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

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 [P
₂O
₇]⁴⁻
reacts with water H
₂O by hydrolysis, which can give hydrogenphosphate:

[P
₂O
₇]⁴⁻
+ H₂O ⇌ 2 [HPO
₄]²⁻