Monopotassium phosphite

Monopotassium phosphite is an inorganic compound with the formula KH₂PO₃. A compositionally related compound has the formula H₃PO₃^.2(KH₂PO₃). Both are white solids that consist of salts of the phosphite anion H₂PO₃⁻, the conjugate base of phosphorous acid.

Monopotassium phosphite

Ball-and-stick model of the component ions
Names
IUPAC name Potassium hydrogen phosphonate
Other names Potassium dihydrogen phosphite; Mono potassium phosphite; Monopotassium dihydrogen phosphite; Potassium phosphite monobasic
Identifiers
CAS Number	13977-65-6 Y
3D model (JSmol)	Interactive image
ECHA InfoCard	100.116.175
PubChem CID	23701737
UNII	59RSS63D8J Y
CompTox Dashboard (EPA)	DTXSID20884521
InChI InChI=1S/K.H2O3P/c;1-4(2)3/h;1-2H/q+1;-1 Key: BZHCGFBZBPVRFE-UHFFFAOYSA-N
SMILES OP(O)[O-].[K+]
Properties
Chemical formula	H2KO3P
Molar mass	120.085 g·mol−1
Appearance	white crystals
Density	2.14 g/cm3
Solubility in water	2200 g/L
Solubility	soluble in ethanol
Structure
Crystal structure	monoclinic
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Phosphites of potassium are used as fungicides (in a loose sense) in agriculture to combat water mold infection. Confusingly, they have also been marketed as fertilizers to avoid a regulatory burden. While perfectly capable to supply potassium to the plant, the phosphorus in phosphite form is unavailable to plants, and may even inhibit the uptake of the normal phosphate form if used in excess.