Hydrogen-iodide (HI)

Hydrogen-iodide (HI)

A colorless, heavier-than-air gas with a pungent odor.



hydrogen iodide, hydrogen halide, molecule, covalent bond, sigma bond, polar, inorganic chemistry, general chemistry, chemistry

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Hydrogen-iodide HI


Molar mass: 127.91 g/mol

Melting point: -51.0 °C (-59.8 °F)

Boiling point: -35.1 °C (-31.18 °F)

Relative steam density (air=1): 4.4


Hydrogen iodide dissolves well in water; the aqueous solution is acidic and reacts intensively with bases. Its salts are called iodides. It is not combustible. It participates in the halogenation reactions of metals, non-metals, hydrides and oxides.

Occurrence and production

In laboratories, it is formed from phosphorus triiodide and water or by adding hydrogen sulfide to the aqueous solution of iodine. In industry, it is synthesized during a reaction of hydrogen and gaseous iodine in the presence of platinum as a catalyst.


It is used in the production of organic or non-organic iodine compounds, such as medicines and fertilizers. It is also used as a reducing agent.

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Comparison of hydrogen halides

Atoms within hydrogen halides are bound by covalent bonds, forming polar molecules.

Hydrogen bromide (HBr)

One of the hydrogen halides, it is used for the production of alkyl bromides.

Hydrogen chloride (HCl)

A colorless gas with a pungent odor, its solution in water is called hydrochloric acid.

Hydrogen-fluoride (HF)

One of the hydrogen halides, a highly aggressive substance - it even attacks glass.

Iodine crystal

A solid, gray substance which sublimates when heated. Its solution in alcohol is called ´tincture of iodine´, it is a disinfectant.

Hydrogen (H₂)

Colorless, odorless, lighter-than-air gas. The most common chemical element in the universe.

Iodine (I₂)

A solid, gray substance which sublimates when heated. Its solution in alcohol is called tincture of iodine, it is a disinfectant.

Silver iodide (AgI)

A light yellow compound formed in the reaction of silver nitrate and potassium iodide.

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