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colorless, rhomb crystal(s) or white, crystal(s) powder(s); darkens on exposure to light; it is a moderately strong acid; used in analytical chemistry and in medicine [HAW93] [MER06]
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Iodic acid, HIO3, can be obtained as a white solid. It
dissolves in water very well, but it also exists in the
pure state, as opposed to chloric acid or bromic acid.
Iodic acid contains iodine in the oxidation state+5
and it is one of the most stable oxo-acids of the halogens
in its pure state. When iodic acid is carefully heated, it
dehydrates to iodine pentoxide. On subsequent heating,
the iodine pentoxide further decomposes, giving
a mixture of iodine, oxygen and lower oxides of iodine.
Iodic acid can be produced by oxidizing I2 with
chlorine in an aqueous solution. Iodic acid can be
used to synthesize sodium or potassium iodate salts
(which are used in salt as a source of iodine in the
human body.
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Iodic acid is used in analytical chemistry laboratories to standardize solutions of both weak and strong bases using methyl red or methyl orange as the indicator. It acts as a key starting material to synthesize sodium or potassium iodate, thereby increasing the iodine content of salt.
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iodic acid: Any of various oxoacids of iodine, such as iodic(V) acid and iodic(VII) acid. When used without an oxidation state specifled, the term usually refers to iodic(V) acid (HIO
3).
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Iodic acid is the hydrated form of I
2O
5. Reaction of iodic acid with hydrogen iodide has been described by electrolytic dissociation theory. Combustion of mixture of chromic, iodic, sulfuric and phosphoric acids has been proposed. Its Raman spectra have been recorded. Vibrational assignment of IO
3- has been evaluated.
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Toxic by ingestion, strong irritant to eyes
and skin.
Purification Methods
Dissolve iodic acid in the minimum volume of hot dilute HNO3, filter and evaporate in a vacuum desiccator until crystals are formed. Collect the crystals and wash them with a little cold H2O and dry them in air in the dark. It is soluble in H2O: 269g/100mL at 20o and 295g/100mL at 40o. It is soluble in dilute EtOH and darkens on exposure to light. It is converted to HIO3.I2O5 on heating at 70o, but at 220o complete conversion to HIO3 occurs. [Lamb et al. J Am Chem Soc 42 1636 1920, Bray & Caulkins J Am Chem Soc 53 44 1931.]
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