Dihydrogen phosphate is an inorganic ion with the formula [H2PO4]−. Phosphates occur widely in natural systems. 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.
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, pKa4 |
|---|---|
| H3PO4 ⇌ H2PO−4 + H+ | pKa1 = 2.145 |
| H2PO−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.6
Notes
References
Tech, Noah. "Sodium Phosphates: From Food to Pharmacology | Noah Technologies". Retrieved 2021-03-23. https://noahchemicals.com/sodium-phosphates/ ↩
Havelange, Sébastien; Lierde, Nicolas; Germeau, Alain; Martins, Emmanuel; Theys, Tibaut; Sonveaux, Marc; Toussaint, Claudia; Schrödter, Klaus; Bettermann, Gerhard; Staffel, Thomas; Wahl, Friedrich; Klein, Thomas; Hofmann, Thomas (2022). "Phosphoric Acid and Phosphates". Ullmann's Encyclopedia of Industrial Chemistry. pp. 1–55. doi:10.1002/14356007.a19_465.pub4. ISBN 978-3-527-30385-4. 978-3-527-30385-4 ↩
PubChem. "Dihydrogen phosphate". pubchem.ncbi.nlm.nih.gov. Retrieved 2021-03-23. https://pubchem.ncbi.nlm.nih.gov/compound/1003 ↩
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. https://doi.org/10.1351%2Fpac200577040739 ↩
Values are at 25 °C and 0 ionic strength. ↩
Tech, Noah. "Sodium Phosphates: From Food to Pharmacology | Noah Technologies". Retrieved 2021-03-23. https://noahchemicals.com/sodium-phosphates/ ↩