Phosphorous acid

Phosphorous acid
Names
	IUPAC name Phosphonic acid
	Systematic IUPAC name Phosphorous acid
	Other names Dihydroxyphosphine oxide; Dihydroxy(oxo)-λ5-phosphane; Dihydroxy-λ5-phosphanone; Orthophosphorous acid; Oxo-λ5-phosphanediol; Oxo-λ5-phosphonous acid; Metaphosphoroic acid
Identifiers
CAS Number	13598-36-2 ;
3D model (JSmol)	HP(O)(OH)2: Interactive image; P(OH)3: Interactive image;
ChEBI	CHEBI:44976 ;
ChEMBL	ChEMBL1235291;
ChemSpider	10449259 ;
ECHA InfoCard	100.033.682
EC Number	237-066-7;
Gmelin Reference	1619
KEGG	C06701 ;
PubChem CID	107909;
RTECS number	SZ6400000;
UNII	35V6A8JW8E ;
UN number	2834
CompTox Dashboard (EPA)	DTXSID2049715 ;
	InChI InChI=1S/H3O3P/c1-4(2)3/h4H,(H2,1,2,3) Key: ABLZXFCXXLZCGV-UHFFFAOYSA-N ; InChI=1/H3O3P/c1-4(2)3/h4H,(H2,1,2,3) Key: ABLZXFCXXLZCGV-UHFFFAOYAF;
	SMILES HP(O)(OH)2: OP(=O)O; P(OH)3: OP(O)O;
Properties
Chemical formula	H3PO3
Molar mass	81.99 g/mol
Appearance	white solid ; deliquescent
Density	1.651 g/cm3 (21 °C)
Melting point	73.6 °C (164.5 °F; 346.8 K)
Boiling point	200 °C (392 °F; 473 K) (decomposes)
Solubility in water	310 g/100 mL
Solubility	soluble in ethanol
Acidity (pKa)	1.3, 6.7
Magnetic susceptibility (χ)	−42.5·10−6 cm3/mol
Structure
Molecular shape	pseudo-tetrahedral
Hazards
	Occupational safety and health (OHS/OSH):
Main hazards	skin irritant
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H302, H314
Precautionary statements	P260, P264, P270, P280, P301+P312, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P330, P363, P405, P501
NFPA 704 (fire diamond)	3 0 1
Safety data sheet (SDS)	Sigma-Aldrich
Related compounds
Related compounds	H3PO4 (i.e., PO(OH)3); H3PO2 (i.e., H2PO(OH))
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Phosphorous acid (or phosphonic acid) is the compound described by the formula H₃PO₃. It is diprotic (readily ionizes two protons), not triprotic as might be suggested by its formula. Phosphorous acid is an intermediate in the preparation of other phosphorus compounds. Organic derivatives of phosphorous acid, compounds with the formula RPO₃H₂, are called phosphonic acids.