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| 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 | |||
| 3D model (JSmol) | |||
| ChEBI | |||
| ChemSpider | |||
| Gmelin Reference | 1998 | ||
| PubChem CID | |||
| UNII | |||
| CompTox Dashboard (EPA) | |||
InChI
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SMILES
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| Properties | |||
| Chemical formula | HPO 4 | ||
| Conjugate acid | Dihydrogen phosphate | ||
| Conjugate base | Phosphate | ||
| Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). Infobox references | |||
Hydrogen phosphate or monohydrogen phosphate (systematic name) is the inorganic ion with the formula . Its formula can also be written as . 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 and a conjugate base of dihydrogen phosphate .
It is formed when a pyrophosphate anion
reacts with water H
2O by hydrolysis, which can give hydrogenphosphate:
+ H2O ⇌ 2
Acid-base equilibria
Hydrogenphosphate is an intermediate in the multistep conversion of phosphoric acid to phosphate:
| Equilibrium | Dissociation constant, pKa |
|---|---|
| H3PO4 ⇌ H 2PO 4 + H |
pKa1 = 2.14 |
| H 2PO 4 ⇌ HPO 4 + H |
pKa2 = 7.20 |
| HPO 4 ⇌ PO 4 + H |
pKa3 = 12.37 |
- Values are at 25 °C and 0 ionic strength.
Examples
- Diammonium phosphate, (NH4)2HPO4
- Disodium phosphate, Na2HPO4, with varying amounts of water of hydration
References
- Schrödter, Klaus; Bettermann, Gerhard; Staffel, Thomas; Wahl, Friedrich; Klein, Thomas; Hofmann, Thomas (2008). "Phosphoric Acid and Phosphates". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a19_465.pub3. ISBN 978-3527306732.
- Powell, Kipton J.; Brown, Paul L.; Byrne, Robert H.; Gajda, Tamás; Hefter, Glenn; Sjöberg, Staffan; Wanner, Hans (2005). "Chemical speciation of environmentally significant heavy metals with inorganic ligands. Part 1: The Hg, Cl, OH, CO
3, SO
4, and PO
4 aqueous systems". Pure Appl. Chem. 77 (4): 739–800. doi:10.1351/pac200577040739.
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