Hydrogen iodide

(Redirected from Hydriodic acid)
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Hydrogen iodide
PubChem {{{value}}}
RTECS number MW3760000
SMILES {{{value}}}
Template:Chembox Elements/molecular formula
Molar mass 127.904 g/mol
Appearance Colorless gas
Density 2.85 g/mL (−47 °C)
Melting point Template:Chembox CalcTemperatures
Boiling point Template:Chembox CalcTemperatures
Acidity (pKa) −10 (in water, estimate);[1] -9.5 (±1.0) [2]

2.8 (in acetonitrile)[3]

0.38 D
Main hazards Toxic, corrosive, Harmful and Irritant
NFPA 704
R-phrases R20, R21, R22, R35
S-phrases Template:S7, Template:S9, S26, S45
Flash point Non-flammable
Related compounds
Other anions Hydrogen fluoride
Hydrogen chloride
Hydrogen bromide
Hydrogen astatide
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Hydrogen iodide (Template:Chemical formula) 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.

Related pages


  1. Bell, R.P. The Proton in Chemistry. 2nd ed., Cornell University Press, Ithaca, NY, 1973.
  2. 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
  3. 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

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