Dihydrogen phosphate

Dihydrogen Phosphate
Names
	IUPAC name Dihydrogen Phosphate
	Systematic IUPAC name Phosphoric acid, ion(1-)
	Other names Phosphoric acid, ion(1-) Dehydrophosphoric acid (1-)
Identifiers
3D model (JSmol)	Interactive image;
PubChem CID	1003;
CompTox Dashboard (EPA)	DTXSID40930897 ;
	SMILES OP(=O)(O)[O-];
Properties
Chemical formula	[H2PO4]-
Molar mass	96.987 g/mol
Conjugate acid	Phosphoric Acid
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Dihydrogen phosphate or dihydrogenphosphate ion is an inorganic ion with the formula [H₂PO₄]⁻. Its formula can also be written as [PO₂(OH)₂]⁻, which shows the presence of two O-H bonds. Together with hydrogen phosphate, dihydrogen phosphate occurs widely in natural systems. Their salts are used in fertilizers and in cooking.^[1] Most dihydrogen phosphate salts are colorless, water soluble, and nontoxic.

Structure

The dihydrogen phosphate anion consists of a central phosphorus atom surrounded by 2 equivalent oxygen atoms and 2 hydroxy groups in a tetrahedral arrangement. The phosphorus atom is in the 5+ oxidation state. The dihydrogen phosphate ion carries an overall charge of −1 and it is the conjugate base of phosphoric acid.

Acid-base equilibria

Dihydrogenphosphate is an intermediate in the multistep conversion of phosphoric acid to phosphate:

Equilibrium	Disassociation constant, pK_a^[2]
H₃PO₄ ⇌ H ₂PO⁻ ₄ + H⁺	pK_a1 = 2.14^[a]
H ₂PO⁻ ₄ ⇌ HPO²⁻ ₄ + H⁺	pK_a2 = 7.20
HPO²⁻ ₄ ⇌ PO³⁻ ₄ + H⁺	pK_a3 = 12.37

Examples

Monocalcium phosphate (Ca(H₂PO₄)₂)
Ammonium dihydrogen phosphate ((NH₄)(H₂PO₄))

Notes

^ Values are at 25 °C and 0 ionic strength.

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

[3] Values are at 25 °C and 0 ionic strength.

[Ullmann-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.

[1]

[2]

[a]