Iodic acid

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Iodic acid
Iodic acid
Ball-and-stick model of iodic acid Space-filling model of iodic acid
Identifiers
CAS number 7782-68-5 YesY
PubChem 24345
ChemSpider 22761 YesY
ChEBI CHEBI:24857 YesY
ChEMBL CHEMBL1161636 YesY
Jmol-3D images Image 1
Properties
Molecular formula HIO3
Molar mass 175.91 g/mol
Appearance White solid
Density 4.62 g/cm3, solid
Melting point 110 °C (230 °F; 383 K)
Solubility in water 269 g/100 mL (20 °C)
Acidity (pKa) 0.75
Hazards
EU Index Not listed
Flash point Non-flammable
Related compounds
Other cations Lithium iodate
Potassium iodate
Related halogen oxoacids Chloric acid
Bromic acid
Related compounds Hydroiodic acid
Iodine pentoxide
Periodic acid
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

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 mix of iodine, oxygen and lower oxides of iodine.

Preparation[edit]

Iodic acid can be produced by oxidizing I2 with strong oxidizers such as Nitric acid HNO
3
, Chlorine Cl
2
, Chloric acid HClO
3
or Hydrogen peroxide H
2
O
2
,[1] for example :

I
2
+ 6 H
2
O
+ 5 Cl
2
is in equilibrium with 2 HIO
3
+ 10 HCl.

Properties[edit]

Iodic acid is a relatively strong acid with a pKa of 0.75. It is strongly oxidizing in acidic solution, less so in basic solution. When iodic acid acts as oxidizer, then the product of the reaction is either iodine, or iodide ion. Under some special conditions (very low pH and high concentration of chloride ion, e.g. in concentrated hydrochloric acid), iodic acid is reduced to iodine trichloride, a golden yellow compound in solution and no further reduction occurs. In the absence of chloride ions, when there is an excess amount of reductant, then all iodate is converted to iodide ion. When there is an excess amount of iodate, then part of the iodate is converted to iodine.

Uses[edit]

Iodic acid is used as a strong acid in analytical chemistry. It may be used to standardize solutions of both weak and strong bases, with methyl red or methyl orange as the indicator.

Use in salt industry[edit]

Iodic acid can be used to synthesize sodium or potassium iodate for increasing iodine content of salt.[citation needed]

References[edit]

  1. ^ (German) Arnold F. Holleman, Nils Wiberg, « Lehrbuch der Anorganischen Chemie », 102. Auflage, Berlin, 2007.