Hydrogen iodide (HI) is a chemical compound. Its chemical formula is HI. It is a colorless odorous gas. It reacts with oxygen to make iodine and water. It can be made by reducing iodine with hydrazine. It can also be made by reacting iodides with non-oxidizing acids such as phosphoric acid. It can also be made by reacting hydrogen sulfide with iodine. Very pure hydrogen iodide can be made by combining hydrogen and iodine, but this is very slow. It will break down if exposed to air. It can be used to make illegal drugs and various chemical compounds of iodine. It dissolves in water to produce hydroiodic acid. Hydroiodic acid is a strong acid that is used to make iodides.
Hydroiodic acid (aqueous solution)
3D model (JSmol)
|Molar mass||127.904 g/mol|
|Density||2.85 g/mL (−47 °C)|
|Melting point||−50.80 °C (−59.44 °F; 222.35 K)|
|Boiling point||−35.36 °C (−31.65 °F; 237.79 K)|
|approximately 245 g/100 ml|
|Acidity (pKa)||−10 (in water, estimate); -9.5 (±1.0)  |
2.8 (in acetonitrile)
|Main hazards||Toxic, corrosive, Harmful and Irritant|
|R-phrases||R20, R21, R22, R35|
|S-phrases||S7, S9, S26, S45|
|Other anions||Hydrogen fluoride|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
- Bell, R.P. The Proton in Chemistry. 2nd ed., Cornell University Press, Ithaca, NY, 1973.
- Trummal, A.; Lipping, L.; Kaljurand, I.; Koppel, I. A.; Leito, I. "Acidity of Strong Acids in Water and Dimethyl Sulfoxide" J. Phys. Chem. A. 2016, 120, 3663-3669. doi:10.1021/acs.jpca.6b02253
- Raamat, E.; Kaupmees, K.; Ovsjannikov, G.; Trummal, A.; Kütt, A.; Saame, J.; Koppel, I.; Kaljurand, I.; Lipping, L.; Rodima, T.; Pihl, V.; Koppel, I. A.; Leito, I. "Acidities of strong neutral Brønsted acids in different media." J. Phys. Org. Chem. 2013, 26, 162-170. doi:10.1002/poc.2946