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Hydroiodic Acid
CAS number 10034-85-2



Identifiers

CAS number [10034-85-2]
RTECS number MW3760000

Properties

Molecular formula HI
Molar mass 127.904 g/mol
Appearance Colorless gas.
Density 2.85 g/mL (-47 °C)
Melting point –50.80 °C (184.55 K)
Boiling point –34.36 °C (237.79 K)
Acidity (pKa) –10

Structure

Molecular shape Terminus
Dipole moment 0.38 D

Related compounds

Other anions Hydrogen fluoride
Hydrogen chloride
Hydrogen bromide

Once again, although chemically related, hydroiodic acid is not HI but made from it. Commercial "concentrated" hydroiodic acid usually contains 48% - 57% HI by weight. The solution forms an azeotrope boiling at 127 °C at 57% HI, 43% water. Hydroiodidic acid is one of the strongest of all the common halide acids, despite the fact that the electronegativity of iodine is weaker than the rest of the other common halides. The high acidity is caused by the dispersal of the ionic charge over the anion. The iodide ion is much larger than the other common halides which results in the negative charge being dispersed over a large space. By contrast, a chloride ion is much smaller, meaning its negative charge is more concentrated, leading to a stronger interaction between the proton and the chloride ion. This weaker H+---I− interaction in HI facilitates dissociation of the proton from the anion .

HI(g) + H2O(l) ⇌ H3O+(aq) + I–(aq) (Ka ≈ 1010)
HBr(g) + H2O(l) ⇌ H3O+(aq) + Br–(aq) (Ka ≈ 109)
HCl(g) + H2O(l) ⇌ H3O+(aq) + Cl–(aq) (Ka ≈ 108)

Appearance Yellow color liquid (57% aqueous solution)

Reactivity It reacts with many metals to generate hydrogen and to form the metal iodides. It acts as a reducing agent on organic compounds.

Specifications

Item ISE Standard JIS K8917-1975 Special Class
Nonvolatile constituents 0.01% max. 0.01% max.
Combustion residue (Sulfate) 0.005% max. 0.005% max.
Hydrochloric acid/ Hydrobromic Acid (as CI) 0.01% max. 0.01% max.
Sulfates (SO4) 0.003% max. 0.003% max.
Phosphates (PO4) 0.001% max. 0.001% max.
Heavy metals (as Pb) 0.001% max. 0.001% max.
Iron (Fe) 0.0005% max. 0.0005% max.
Arsenic (As) 0.0001% max. 0.0001% max.
Free iodine (I) 0.06% max. 0.76% max.
Sulfide
To pass test
Appearance (Slightly red)
Assay A: 56% min. 55 ~ 58%
B: 57% min.

Packaging

Outside packing Special plastic container (20l)
Net weight 30 kg (Sealed with nitrogen gas)


Applications

Reducing agent
Iodide synthesis material
Germicides
Medicines
Preparation of inorganic iodides (KI, NaI, NH4I, AgI, etc.)
Preparation of inorganic iodides (iodobenzoic acids or similar compounds for X-ray contrast intermediates, aliphatic iodides, etc.)
Disinfectant and Sanitizer formulations

Health Hazards
1) Fire and explosion: Non-explosive; Water sprinkling is advised to extinguish fire.
2) Gas generation: HI fumes
3) Others Strong mono-basic acid

First aid

1) Rinse eyes with water immediately.
2) Wash contaminated skin areas with soap and dilute aqueous sodium carbonate solution.
3) When taken orally, wash the stomach a 5% aqueous solution of calcium chloride, and administer a self-containing purgative.
4) Oxygen inhalation, and calcium-rich food have been found effective.

Handling & Storage

1) Tightly seal the container and store in a cool, dark, well ventilated place
2) Use rubber gloves, fully body protection garments and gas mask.
3) Mixing and contact hazardous materials: Alkali metals

Spillage

Diluted with water, then cover spilled hydroiodic acid with sodium bicarbonate or a mixture of soda ash and slaked lime (50 : 50). Mix together, and add water if necessary to produce a slurry. Collect the slurry into a container, and wash contaminated surfaces with a large amount of water.

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