Hypoiodous acid is an inorganic compound with the chemical formula HOI.It forms when an aqueous solution of iodine is treated with mercuric or silver salts. It rapidly decomposes by disproportionation:^[1]

5 HIO → HIO₃ + 2 I₂ + 2 H₂O

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Hypoiodous acid

Hydrogen, H   Oxygen, O   Iodine, I
Names
IUPAC name Hypoiodous acid
Identifiers
CAS Number	14332-21-9 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:29231 Y
ChemSpider	109942 Y
PubChem CID	123340
UNII	2PYC923C5W Y
CompTox Dashboard (EPA)	DTXSID8042050
InChI InChI=1S/HIO/c1-2/h2H Y Key: GEOVEUCEIQCBKH-UHFFFAOYSA-N Y
SMILES IO
Properties
Chemical formula	HOI
Molar mass	143.911 g·mol−1
Acidity (pKa)	10.5 (in water, estimate)
Conjugate base	Hypoiodite
Related compounds
Related compounds	Hypofluorous acid Hypochlorous acid Hypobromous acid
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

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Hypoiodites of alkali and alkaline earth metals can be made in cold dilute solutions if iodine is added to their respective hydroxides. Hypoiodous acid is a weak acid with a pK_a of about 11. The conjugate base is hypoiodite (IO⁻). Salts of this anion can be prepared by treating I₂ with alkali hydroxides. They rapidly disproportionate to form iodides and iodates.^[1]