Hydrogen phosphateormonohydrogen 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.[1] Most hydrogenphosphate salts are colorless, water soluble, and nontoxic.
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| Names | |||
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| Preferred IUPAC name
Hydrogenphosphate | |||
| Systematic IUPAC name
Monohydrogenphosphate | |||
| Other names
Phosphoric acid, ion(2-) | |||
| Identifiers | |||
3D model (JSmol) |
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| ChemSpider | |||
| 1998 | |||
PubChem CID |
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CompTox Dashboard (EPA) |
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| Properties | |||
| 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).
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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
2Obyhydrolysis, which can give hydrogenphosphate:
Hydrogenphosphate is an intermediate in the multistep conversion of phosphoric acidtophosphate:
| Equilibrium | Dissociation constant, pKa[2] |
|---|---|
| H3PO4 ⇌ H 2PO− 4 + H+ |
pKa1 = 2.14[a] |
| H 2PO− 4 ⇌ HPO2− 4 + H+ |
pKa2 = 7.20 |
| HPO2− 4 ⇌ PO3− 4 + H+ |
pKa3 = 12.37 |
