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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