Monohydrogen phosphate

Monohydrogen phosphate is the inorganic ion with the formula [HPO4]2-. Its formula can also be written as [PO3(OH)]2-, which shows the presence of a O-H bond. Together with dihydrogen phosphate, monohydrogen phosphate occurs widely in natural systems. Their salts are used in fertilizers and in cooking.[1] Most monohydrogenphosphate salts are colorless, water soluble, and nontoxic.

Monohydrogen phosphate anion.

Acid-base equilibria

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

Equilibrium Disassociation constant, pKa[2]
H3PO4 ⇌ H
2PO−
4 + H+		 pKa1 = 2.14[lower-alpha 1]
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
gollark: It's not particularly evil, since it will only be used to identify opting-in things.
gollark: But I skimmed a paper on it and apparently the randomization can be workarounded in some cases by sending RTS frames with the device's "hardcoded" MAC address and seeing if you get a CTS frame back.
gollark: This would have been doable by just checking the MAC address against a list several years ago, but evil beeoids also did this so now phones and such have randomization.
gollark: Well, for convoluted reasons, I want to detect known devices within wireless range.
gollark: Request to send.

References
  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.
  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.
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