Dihydrogen phosphate

Dihydrogen phosphate is an inorganic ion with the formula [H₂PO₄]⁻. Phosphates occur widely in natural systems.^[1] Perhaps the most common salt of dihydrogen phosphate is sodium dihydrogen phosphate. It is used in animal feed, fertilizer, buffer (in food), and treating metal surfaces.^[2]

Dihydrogen phosphate

Names
IUPAC name Dihydrogenphosphate
Systematic IUPAC name Phosphoric acid, ion(1−)
Other names Phosphoric acid, ion(1−) Dehydrophosphoric acid (1−)
Identifiers
CAS Number	14066-20-7 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:39745
ChemSpider	978
DrugBank	DB02831
Gmelin Reference	1999
PubChem CID	1003
CompTox Dashboard (EPA)	DTXSID40930897
InChI InChI=1S/H3O4P/c1-5(2,3)4/h(H3,1,2,3,4)/p-1 Key: NBIIXXVUZAFLBC-UHFFFAOYSA-M
SMILES OP(=O)(O)[O-]
Properties
Chemical formula	H2O4P−1
Molar mass	96.986 g·mol−1
Conjugate acid	Phosphoric Acid
Related compounds
Related compounds	Phosphate, Monohydrogen phosphate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Structure

The dihydrogen phosphate anion consists of a central phosphorus atom bonded two oxides and two hydroxy groups in a tetrahedral arrangement.^[3]

Acid-base equilibria

Dihydrogen phosphate can be both a hydrogen donor and acceptor.

Equilibrium	Disassociation constant, pKa[4]
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

Examples

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

Safety

Many foods including milk, eggs, poultry, and nuts contain these sodium phosphates.^[1]

Notes

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