Iodic acid

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Iodic acid
IUPAC name
Iodic acid
Preferred IUPAC name
Iodic acid
Systematic IUPAC name
Iodic acid
Other names
Iodic(V) acid
Trioxoiodic(V) acid
Molar mass 175.91 g/mol
Appearance White solid
Odor Odorless
Density 4.62 g/cm3 (20 °C)
Melting point 110 °C (230 °F; 383 K) [4]
Boiling point 200 °C (392 °F; 473 K) (decomposes)
236.7 g/100 ml (0 °C)
253.4 g/100 ml (16 °C)
280.2 g/100 ml (40 °C)
360.8 g/100 ml (100 °C)[1][2]
Solubility Soluble in sulfuric acid
Moredately soluble in ethanol, methanol
Insoluble in glacial acetic acid, carbon disulfide, chloroform, diethyl ether, perchloric acid[3]
Vapor pressure ~0 mmHg
Acidity (pKa) 0.75
-243.1 kJ/mol
Safety data sheet Sigma-Aldrich
Flash point Non-flammable
Related compounds
Related compounds
Chloric acid
Bromic acid
Periodic acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Iodic acid is a chemical compound, a solid inorganic acid with the chemical formula HIO3. Unlike its other halogen equivalents, namely chloric acid and bromic acid, iodic acid is one of the most stable oxo-acids of the halogens.



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.

When iodic acid is added to an aq. solution of sodium hydroxide, sodium iodate is produced.

HIO3 + NaOH → NaIO3 + H2O

When heated to 200 °C, iodic acid dehydrates to give iodine pentoxide. If excess heat is used, the resulting iodine pentoxide further decomposes to iodine and oxygen.

2 HIO3 → I2O5 + H2O
I2O5 → I2 + 5/2 O2


Iodic acid is a white solid, very soluble in water.


Iodic acid is sold by chemical suppliers. Can also be bought online.


Iodic acid can be produced by oxidizing elemental iodine with chlorine, in water.

I2 + 6 H2O + 5 Cl2 ⇌ 2 HIO3 + 10 HCl

Other oxidizers, such as nitric acid[5][6], chloric acid[7], bromine[8], ozone[9][10] or hydrogen peroxide[11] can also be used.[12]

Addition of iodine trichloride to water will produce iodic acid and other side products, depending on the temperature:

2 ICl3 + 3 H2O → 5 HCl + HIO3 + ICl (cold water)
5 ICl3 + 9 H2O → 15 HCl + 3 HIO3 + I2 (hot water)

Adding iodine pentoxide to water will form very pure iodic acid.[13]

I2O5 + H2O → 2 HIO3

Very pure and concentrated iodic acid can also be produced by adding concentrated sulfuric acid to calcium or barium iodate, with the resulting insoluble calcium and barium sulfate being filtered off.[14][15]

Ca(IO3)2 + H2SO4 → 2 HIO3 + CaSO4
Ba(IO3)2 + H2SO4 → 2 HIO3 + BaSO4

Adding elemental iodine to an aq. solution of silver iodide and heating the solution will precipitate silver iodide and yield iodic acid.[16]

Reduction of periodic acid with a suitable reducing agent, such as aq. sulfur dioxide will yield iodic acid.[17]

Adding nitrogen trichloride to an aq. suspension of iodine is described as producing iodic acid.[18]


  • Make iodate salts
  • Make iodine pentoxide



Iodic acid is irritant, corrosive and oxidizer. Wear proper protection when handling the compound.


In closed glass bottles.


Can be reduced to iodide if necessary.


  1. Рабинович В.А., Хавин З.Я. Краткий химический справочник. - Л.: Химия, 1977 (Rabinovich V.A., Khavin Z.Ya. A short chemical reference book. - L .: Chemistry, 1977)
  2. Справочник по растворимости. - Т.1, Кн.1. - М.-Л.: ИАН СССР, 1961 (Solubility Handbook. - Vol. 1, Book 1. - M.-L .: IAN USSR, 1961 )
  3. Рабинович В.А., Хавин З.Я. Краткий химический справочник. - Л.: Химия, 1977 (Rabinovich V.A., Khavin Z.Ya. A short chemical reference book. - L .: Chemistry, 1977 )
  4. Baxter, G. P.; Tilley, G. St.; Journal of the American Chemical Society; vol. 31; (1909); p. 205
  5. Scott, A.; Arbuckle, W.; Journal of the Chemical Society; vol. 79; (1901); p. 302
  6. Perez-Vitoria, A.; Garrido, J.; Anales de la Real Sociedad Espanola de Fisica y Quimica; vol. 30; (1932); p. 13
  7. Lamb; Bray; Geldard; Journal of the American Chemical Society; vol. 42; (1920); p. 1636 - 1636
  8. Bugarszky, St.; Horvath, B.; Z. Anorg. Chem.; vol. 63; (1909); p. 184
  9. Engler, C.; Wild, W.; Ber.; vol. 29; (1896); p. 1929
  10. Biedermann, Georg; Lendeus, Roland; Acta Chemica Scandinavica, Series A: Physical and Inorganic Chemistry; vol. 38; (1984); p. 825 - 827
  11. Bray, W. C.; Caulkins, A. L.; Journal of the American Chemical Society; vol. 53; (1931); p. 44
  12. Holleman, Arnold F.; Wiberg, Nils (2007). Lehrbuch der Anorganischen Chemie (in German) (102nd ed.). Berlin
  13. IODINE Its Properties and Technical Applications, CHILEAN IODINE EDUCATIONAL BUREAU, INC., 120 Broadway, New York 5, New York, 1951
  14. Reichardt, E.; Archiv der Pharmazie (Weinheim, Germany); vol. 205; (1874); p. 109 - 111
  15. Stevenson, W.; Chem. News J. Ind. Sci.; vol. 36; (1877); p. 201
  16. Naquet, A.; Bulletin de la Societe Chimique de France; (1858); p. 126 - 129
  17. Selmons, F.; Ber.; vol. 21; (1888); p. 230
  18. Sseliwanow; Zh. Russ. Fiz. - Khim. O - va., Chast Khim.; vol. 26; (1894); p. 541 - 541

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