Hydrogen phosphate
Stereo skeletal formula of hydrogenphosphate
Aromatic ball and stick model of hydrogenphosphate
Aromatic ball and stick model of hydrogenphosphate
Space-filling model of hydrogenphosphate
Space-filling model of hydrogenphosphate
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
3D model (JSmol)
ChEBI
ChemSpider
1998
UNII
  • InChI=1S/H3O4P/c1-5(2,3)4/h(H3,1,2,3,4)/p-2
    Key: NBIIXXVUZAFLBC-UHFFFAOYSA-L
  • OP(=O)([O-])[O-]
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).
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.[1] 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:

Equilibrium Dissociation constant, pKa[2]
H3PO4 ⇌ H
2PO−
4 + H+		 pKa1 = 2.14[lower-alpha 1]
H
2PO−
4 ⇌ HPO2−
4 + H+		 pKa2 = 7.20
HPO2−
4 ⇌ PO3−
4 + H+		 pKa3 = 12.37
  1. ↑ Values are at 25 °C and 0 ionic strength.

Examples

References

  1. ↑ 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.
  2. ↑ 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 Hg2+, Cl−, OH−, CO2−
    3    , SO2−
    4    , and PO3−
    4     aqueous systems"    . Pure Appl. Chem. 77 (4): 739–800. doi:10.1351/pac200577040739.
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