Iodic acid

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Iodic acid
Iodic acid Iodic acid.svg
Iodic acid
Ball-and-stick model of iodic acid Iodic-acid-gamma-polymorph-side-3D-bs-17.png
Ball-and-stick model of iodic acid
Space-filling model of iodic acid Iodic-acid-gamma-polymorph-side-3D-sf.png
Space-filling model of iodic acid
Names
Other names
Iodic(V) acid
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.029.056 OOjs UI icon edit-ltr-progressive.svg
PubChem CID
UNII
  • InChI=1S/HIO3/c2-1(3)4/h(H,2,3,4) Yes check.svgY
    Key: ICIWUVCWSCSTAQ-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/HIO3/c2-1(3)4/h(H,2,3,4)
    Key: ICIWUVCWSCSTAQ-UHFFFAOYAT
  • O[I+2]([O-])[O-]
Properties
HIO3
Molar mass 175.91 g/mol
AppearanceWhite 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]
Conjugate base Iodate
48.0·10−6 cm3/mol
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
acid, corrosive, oxidant
GHS labelling: [2]
GHS-pictogram-rondflam.svg GHS-pictogram-acid.svg
Danger
NFPA 704 (fire diamond)
NFPA 704.svgHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 0: Will not burn. E.g. waterInstability 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calciumSpecial hazard OX: Oxidizer. E.g. potassium perchlorate
3
0
1
OX
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 otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Yes check.svgY  verify  (what is  Yes check.svgYX mark.svgN ?)

Iodic acid is a white water-soluble solid with the chemical formula 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, oxygen and lower oxides of iodine.

Contents

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:

I2 + 6H2O + 5Cl2 ⇌ 2HIO3 + 10HCl

Iodic acid is also produced by the reaction of iodine monochloride with water:

5ICl + 3H2O → 5HCl + HIO3 + 2I2

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 iodine, or 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 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.[ 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
FormulaHIHIOHIO2HIO3HIO4 or H5IO6

References

  1. 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. "Iodic acid" (PDF). Archived from the original (PDF) on 2014-09-26. Retrieved 2022-01-30.
  3. 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)
  4. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 863. ISBN   978-0-08-037941-8.
  5. 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. 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. 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. 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.