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Hydroiodic Acid Formula

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  • Last Updated : 14 Sep, 2022
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Hydroiodic Acid is an aqueous hydrogen iodide solution. It is formed when hydrogen iodide gas is dissolved in water. A molecule is composed of a hydrogen atom and an iodine atom in its anhydrous state. It is a colourless liquid with an unpleasant odour. It has a cooling, saline-strong flavour and is odourless. It is commercially prepared by reacting iodine with hydrazine, which produces hydrogen iodide and nitrogen gas. Because of the remarkable stability of its corresponding conjugate base, it is one of the strongest of the common halide acids. The chemical formula of Hydroiodic acid is HI.

Structure of Hydroiodic Acid

Hydroiodic Acid structure

Hydroiodic Acid structure

Physical Properties of Hydroiodic Acid

Molecular weight of Hydroiodic Acid127.91 g/mol
Density1,700 g/cm³
Boiling Point-35.36 °C
Melting Point-51 °C
OdourPungent odour
AppearanceColourless liquid
Covalently-Bonded Unit1
Heat of vaporization17.36 kJ/mol at 25°C
Hydrogen Bond Donor1
SolubilitySoluble in water

Chemical Properties of Hydroiodic Acid

  • When hydroiodic acid reacts with fuming nitric acid, it produces iodine, nitrogen oxide, and water. 

2HNO3 + 6HI → 2NO + 3I2 + 4H2O

  • When hydroiodic acid reacts with a base, such as sodium hydroxide, it produces sodium iodide and water. 

HI + NaOH → NaI + H2O

Uses of Hydroiodic Acid

  • It is used in the production of iodides, as a reducing agent, disinfectants, and medicines.
  • One of the primary iodine sources in organic and inorganic synthesis.
  • In addition to potassium iodide, hydroiodic acid is a logical choice as a source of a nucleophile in ketal deprotection.

FAQs on Hydroiodic Acid Formula 

Question 1: What happens when you consume hydroiodic acid?


Symptoms of hydrochloric acid consumption include intense pain in the mouth and throat, drooling and breathing difficulties due to throat swelling.

Question 2: How should hydroiodic acid be stored?


Hydroiodic acid must be stored in a dark area, in dark glass bottles that are protected from atmospheric oxygen.

Question 3: Why is hydroiodic acid such a strong acid?


It does not entirely dissociate in water and has a reversible reaction with it. Hydrogen iodide completely dissociates in solution, making it a strong acid.

Question 4: Is HI water soluble?


HI is a colourless gas that, when combined with oxygen, produces water and iodine. HI emits a mist (or vapours) of hydroiodic acid when exposed to moist air. It is very soluble in water and  producing hydroiodic acid.

Question 5: Is HI polar or nonpolar?


Hydrogen iodide (HI) Note the symmetry of the molecule: When divided, the top and bottom, as well as the left and right, are not mirror reflections of one another. The molecule is also known to be polar since the bond is polar.

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