3D model (JSmol)
|Density||1.70 g/mL, azeotrope|
(57% HI by weight)
|Boiling point||127 °C (261 °F; 400 K) 1.03 bar, azeotrope|
|S-phrases (outdated)||(S1/2), S26, S45|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Hydroiodic acid (or hydriodic acid) is a highly acidic aqueous solution of hydrogen iodide (HI) (concentrated solution usually 48 - 57% HI). It is the second strongest hydrohalic acid, after hydroastatic acid. Hydroiodic acid is a commonly used chemical reagent and is one of the strong acids that ionize completely in an aqueous solution.
Hydroiodic acid readily reacts with oxygen in air, contributing to the deep colours associated with old samples;
Like other halogens, hydroiodic acid will perform addition reactions with unsaturated hydrocarbons such as alkenes.
Hydroiodic acid is listed as a U.S. Federal DEA List I Chemical, owing to its use as a reducing agent related to the production of methamphetamine from pseudoephedrine (recovered from nasal decongestant pills).