Iodic acid

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Iodic acid
IUPAC name iodic acid
Identifiers
InChI InChI=InChI=1S/HIO3/c2-1(3)4/h(H,2,3,4)
InChIKey ICIWUVCWSCSTAQ-UHFFFAOYAT
Standard InChI InChI=1S/HIO3/c2-1(3)4/h(H,2,3,4)
Standard InChIKey ICIWUVCWSCSTAQ-UHFFFAOYSA-N
CAS number [7782-68-5]
EC number 231-962-1
ChemSpider 22761
Properties[1][2]
Chemical formula HIO3
Molar mass 175.91 g mol−1
Appearance white crystals
Density 4.629 g cm−3
Melting point

100 °C decomp.

Solubility in water 286 g/100 ml (0 °C)
473 g/100 ml (80 °C)
Acidity (pKa) 0.804
Structure[1]
Molecular geometry pyramidal; r(I=O) = 181 pm, r(I–OH) = 189 pm, O=I=O = 101.4°, O=I–OH = 97°
Hazards[3]
EU index number not listed
GHS pictograms Ox. Sol. 2Skin Corr. 1C, Eye Dam. 1
GHS signal word DANGER
GHS hazard statements H272, H314, H318
GHS precautionary statements P210, P220, P221, P260, P264, P280, P301+330+331, P303+361+353, P363, P304+340, P310, P321, P305+351+338, P370+378
Flash point non-flammable
Related compounds
Other halic acids Chloric acid
Bromic acid
Other compounds Hydroiodic acid
Hypoiodous acid
Periodic acid
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)

Iodic acid, HIO3, is a moderately strong oxoacid of iodine. It forms a series of salts called iodates.

Iodic acid may be prepared by the oxidation of suspensions of iodine in water, either by electrolysis or with nitric acid.[1] Unlike chloric and bromic acids, it can be isolated as a white crystalline air-stable solid. The solid decomposes on heating, first to anhydro-iodic acid, HIO3·I2O5 or HI3O8, at about 100 °C, then to iodine pentoxide at about 200 °C.[1]

Iodic acid is used as primary standard strong acid in acid–base titrations because it can be weighed as a pure solid and has a relatively high molar mass. However, the solid cannot be dried in a 110 °C oven because of dehydration, and recrystallization is difficult because of the high solubility of HIO3: for these reasons, potassium biiodate is usually preferred as a strong-acid standard.

Notes and references

Notes

References

  1. 1.0 1.1 1.2 1.3 Greenwood, Norman N.; Earnshaw, A. Chemistry of the Elements; Pergamon: Oxford, 1984; p 1010. ISBN 0-08-022057-6.
  2. CRC Handbook of Chemistry and Physics, 62nd ed.; Weast, Robert C., Ed.; CRC Press: Boca Raton, FL, 1981; p B-106. ISBN 0-8493-0462-8.
  3. HSNO Chemical Classification Information Database, <http://www.ermanz.govt.nz/Chemicals/ChemicalDisplay.aspx?SubstanceID=12620> (accessed 9 September 2010), New Zealand Environmental Risk Management Authority.

External links

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