Iodic acid

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Iodic acid
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Names
Other names
Iodic(V) acid
Identifiers
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3D model (JSmol)
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  • InChI=1S/HIO3/c2-1(3)4/h(H,2,3,4) checkY
    Key: ICIWUVCWSCSTAQ-UHFFFAOYSA-N checkY
  • InChI=1/HIO3/c2-1(3)4/h(H,2,3,4)
    Key: ICIWUVCWSCSTAQ-UHFFFAOYAT
  • O[I+2]([O-])[O-]
Properties
HIO3
Molar mass 175.909 g·mol−1
Appearance White solid
Density 4.62 g/cm3, solid
Melting point 110 °C (230 °F; 383 K)
269 g/100 mL (20 °C)
Acidity (pKa) 0.75[1]
−48.0·10−6 cm3/mol
Hazards
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3
0
1
OX
Flash point Non-flammable
Related compounds
Other cations
 Lithium iodate
Potassium iodate
Chloric acid
Bromic acid
Related compounds
 Hydroiodic acid
Iodine pentoxide
Periodic acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

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Iodic acid is a white water-soluble solid with the chemical formula Page Module:Chem2/styles.css has no content.HIO3. Its robustness contrasts with the instability of chloric acid and bromic acid. Iodic acid features iodine in the oxidation state +5 and is one of the most stable oxo-acids of the halogens. When heated, samples dehydrate to give iodine pentoxide. On further heating, the iodine pentoxide further decomposes, giving a mix of iodine and oxygen vapors.

Preparation

Iodic acid can be produced by oxidizing iodine with strong oxidizers such as nitric acid, chlorine, chloric acid or hydrogen peroxide,[3] for example:

Page Module:Chem2/styles.css has no content.I2 + 6 H2O + 5 Cl2 ⇌ 2 HIO3 + 10HCl

Iodic acid is also produced by the hydrolysis of iodine chlorides,

Page Module:Chem2/styles.css has no content.5 ICl + 3 H2O → 5 HCl + HIO3 + 2 I2
Page Module:Chem2/styles.css has no content.5 ICl3 + 9 H2O → 15 HCl + 3 HIO3 + I2

although all methods involving chlorine in acidic coditions produce tetrachloroiodic acid as a byproduct:

Page Module:Chem2/styles.css has no content.HIO3 + 6 HCl ⇌ HICl4 + Cl2 + 3 H2O

Structure

Iodic acid crystallises from acidic solution as orthorhombic α-HIO
3 in space group P212121. The structure consists of pyramidal molecules linked by hydrogen bonding and intermolecular iodine-oxygen interactions. The I=O bond lengths are 1.81 Å while the I–OH distance is 1.89 Å.[4][5][6] Several other polymorphs have been reported, including an orthorhombic γ form in space group Pbca[7] and an orthorhombic δ form in space group P212121.[8] All of the polymorphs contain pyramidal molecules, hydrogen bonding and I···O interactions, but differ in packing arrangement.

Properties

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 elemental iodine or the iodide ion. Under some special conditions (very low pH and high concentration of chloride ions, such as in concentrated hydrochloric acid), iodic acid is reduced to iodine trichloride, a golden yellow compound which is present in solution as tetrachloroiodic acid. 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.[citation needed]

Uses

Iodic acid is used as a strong acid (though it is not truly a strong acid, but a weak acid that is very close to being a strong acid) in analytical chemistry. It may be used to standardize solutions of both weak and strong bases, using methyl red or methyl orange as the indicator.

Use in salt industry

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

Other oxyacids

Iodic acid is part of a series of oxyacids in which iodine can assume oxidation states of −1, +1, +3, +5, or +7. A number of neutral iodine oxides are also known.

Iodine oxidation state −1 +1 +3 +5 +7
Name Hydrogen iodide Hypoiodous acid Iodous acid Iodic acid Periodic acid
Formula HI HIO HIO2 HIO3 HIO4 or H5IO6

References

  1. ^ Page Module:Citation/CS1/styles.css has no content.Perrin, D. D., ed. (1982) [1969]. Ionisation Constants of Inorganic Acids and Bases in Aqueous Solution. IUPAC Chemical Data (2nd ed.). Oxford: Pergamon (published 1984). Entry 127. ISBN 0-08-029214-3. LCCN 82-16524.
  2. ^ Page Module:Citation/CS1/styles.css has no content."Iodic acid" (PDF). Archived from the original (PDF) on 2014-09-26. Retrieved 2022-01-30.
  3. ^ Page Module:Citation/CS1/styles.css has no content.Holleman, Arnold F.; Wiberg, Nils (2007). Lehrbuch der Anorganischen Chemie (in German) (102nd ed.). Berlin. ISBN 978-3-11-017770-1.{{cite book}}: CS1 maint: location missing publisher (link) CS1 maint: unrecognized language (link)
  4. ^ Page Module:Citation/CS1/styles.css has no content.Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 863. doi:10.1016/C2009-0-30414-6. ISBN 978-0-08-037941-8.
  5. ^ Page Module:Citation/CS1/styles.css has no content.Rogers, Max T.; Helmholz, Lindsay (1941). "The Crystal Structure of Iodic Acid". J. Am. Chem. Soc. 63 (1): 278–284. doi:10.1021/ja01846a068.
  6. ^ Page Module:Citation/CS1/styles.css has no content.Ståhl, Kenny; Szafranski, Marek (1992). "A Single-Crystal Neutron Diffraction Study of HIO3 at 295 and 30 K and of DIO3 at 295 K". Acta Chem. Scand. 46: 1146–1148. doi:10.3891/acta.chem.scand.46-1146.
  7. ^ Page Module:Citation/CS1/styles.css has no content.Fischer, Andreas; Lindsjö, Martin (2005). "γ-HIO3 – a Metastable, Centrosymmetric Polymorph of Iodic Acid". Z. Anorg. Allg. Chem. 631 (9): 1574–1576. doi:10.1002/zaac.200500099.
  8. ^ Page Module:Citation/CS1/styles.css has no content.Wu, Tao; Zavalij, Peter Y.; Zachariah, Michael R. (2017). "Crystal structure of a new polymorph of iodic acid, δ-HIO3, from powder diffraction". Powder Diffraction. 32 (4): 261–264. Bibcode:2017PDiff..32..261W. doi:10.1017/S0885715617000859. S2CID 104100313.

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