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What is Hydroiodic Acid?

The aqueous solution of hydrogen iodine is named as the hydroiodic acid and it is quite common and acidic too among hydrohalides. The chemical formula for the substance is HI with a molar mass of 127.91g/mol. The substance is available in the gaseous form and hydroiodic acid is the aqueous solution of HI and interchangeable with hydrogen chloride. This is a diatomic molecule with the following structure.

Hydroiodic Acid Formula

Hydroiodic Acid Chemical Formula

This is polarized in nature and connected to each other due to electronegativity nature of the iodine compound. Because of the large size of iodine ion, the negative charge gets dispersed and results in a weaker HI bond. It allows H+ to dissociate quickly and quite stronger when compared to others like HCl, HBr or HF etc.

It can be prepared commercially as well when reacts to I2 and nitrogen gas too. Take the bubbling sulfide gas and mix with the aqueous solution of iodine as shown below –

2 I2 + NH2NH2 → 4 HI + N2H2S + I2 → 2 HI + S

Hydroiodic Acid Molecular

In the end, you can see that HI will get distilled to give the hydroiodic acid in the needed concentration. It is colorless in nature with an acrid odor and quickly soluble in the water to make the hydrochloride acid. The concentration of hydroiodic acid in water is usually 48 percent to 57 percent. The physical properties of the acid largely depend in the HI concentration in the aqueous solution. It is quite reactive so you should use it carefully otherwise it may react violently with ammonia or metal powders etc.

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