Monohydrogen phosphate

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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).

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[a]
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. ISBN 978-3527306732
    .
  2. doi:10.1351/pac200577040739
    .
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