Dihydrogen phosphate
{{short description|Inorganic ion}}
{{Chembox
| Name = Dihydrogen phosphate
| ImageFile = Dihydrogen phosphate.svg
| OtherNames = Phosphoric acid, ion(1−)
Dehydrophosphoric acid (1−)
| IUPACName = Dihydrogenphosphate
| SystematicName = Phosphoric acid, ion(1−)
| Section1 = {{Chembox Identifiers
| CASNo = 14066-20-7
| CASNo_Ref = {{Cascite|correct|CAS}}
| ChEBI = 39745
| ChemSpiderID = 978
| DrugBank = DB02831
| Gmelin = 1999
| PubChem = 1003
| SMILES = OP(=O)(O)[O-]
| StdInChI=1S/H3O4P/c1-5(2,3)4/h(H3,1,2,3,4)/p-1
| StdInChIKey = NBIIXXVUZAFLBC-UHFFFAOYSA-M
}}
| Section2 = {{Chembox Properties
| H=2|P=1|O=4|Formula_Charge = −1
| ConjugateAcid = Phosphoric Acid
}}
| Section3 =
| Section4 =
| Section5 =
| Section8 = {{Chembox Related
| OtherCompounds = Phosphate, Monohydrogen phosphate
}}
}}
Dihydrogen phosphate is an inorganic ion with the formula [H2PO4]−. Phosphates occur widely in natural systems.{{cite web |last=Tech |first=Noah |title=Sodium Phosphates: From Food to Pharmacology {{!}} Noah Technologies |url=https://noahchemicals.com/sodium-phosphates/ |access-date=2021-03-23 |language=en}} 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.{{cite book |doi=10.1002/14356007.a19_465.pub4 |chapter=Phosphoric Acid and Phosphates |title=Ullmann's Encyclopedia of Industrial Chemistry |date=2022 |last1=Havelange |first1=Sébastien |last2=Lierde |first2=Nicolas |last3=Germeau |first3=Alain |last4=Martins |first4=Emmanuel |last5=Theys |first5=Tibaut |last6=Sonveaux |first6=Marc |last7=Toussaint |first7=Claudia |last8=Schrödter |first8=Klaus |last9=Bettermann |first9=Gerhard |last10=Staffel |first10=Thomas |last11=Wahl |first11=Friedrich |last12=Klein |first12=Thomas |last13=Hofmann |first13=Thomas |pages=1–55 |isbn=978-3-527-30385-4 }}
Structure
The dihydrogen phosphate anion consists of a central phosphorus atom bonded two oxides and two hydroxy groups in a tetrahedral arrangement.{{cite web |last=PubChem |title=Dihydrogen phosphate |url=https://pubchem.ncbi.nlm.nih.gov/compound/1003 |access-date=2021-03-23 |website=pubchem.ncbi.nlm.nih.gov |language=en}}
Acid-base equilibria
Dihydrogen phosphate can be both a hydrogen donor and acceptor.
| class="wikitable"
! Equilibrium ! Disassociation constant, pKa{{cite journal | last1=Powell | first1=Kipton J. | last2=Brown | first2=Paul L. | last3=Byrne | first3=Robert H. | last4=Gajda | first4=Tamás | last5=Hefter | first5=Glenn | last6=Sjöberg | first6=Staffan | last7=Wanner | first7=Hans | title=Chemical speciation of environmentally significant heavy metals with inorganic ligands. Part 1: The Hg2+, Cl−, OH−, {{chem|CO|3|2−}}, {{chem|SO|4|2−}}, and {{chem|PO|4|3−}} aqueous systems | journal=Pure Appl. Chem. | date=2005 | volume=77 | issue=4 | pages=739–800 | doi=10.1351/pac200577040739 | doi-access=free }} |
| H3PO4 {{eqm}} {{chem|H|2|PO|4|−}} + H+
| pKa1 = 2.14{{efn|Values are at 25{{nbsp}}°C and 0 ionic strength.}} |
| {{chem|H|2|PO|4|−}} {{eqm}} {{chem|HPO|4|2−}} + H+
| pKa2 = 7.20 |
| {{chem|HPO|4|2−}} {{eqm}} {{chem|PO|4|3−}} + H+
| pKa3 = 12.37 |
Examples
- Ammonium dihydrogen phosphate ((NH4)(H2PO4))
- Monocalcium phosphate (Ca(H2PO4)2)
Safety
Notes
{{Notelist}}