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, hydrogen phosphate 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⁻

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

References