Difference between revisions of "Potassium biiodate"

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   }}
 
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| Section2 = {{Chembox Properties
 
| Section2 = {{Chembox Properties
|  Reference = <ref name="RubberBible">{{RubberBible62nd|page=B-133}}.</ref>
+
|  Reference = <ref name="RubberBible">{{RubberBible62nd|page=B-133}}.</ref><ref name="Struct">{{citation | first1 = Lilian Y. Y. | last1 = Chan | first2 = F. W. B. | last2 = Einstein | title = The Crystal Structure of KIO<sub>3</sub>·HIO<sub>3</sub> | journal = Can. J. Chem. | year = 1971 | volume = 49 | pages = 468–76 | url = http://article.pubs.nrc-cnrc.gc.ca/ppv/RPViewDoc%3Fissn%3D1480-3291&volume%3D49&issue%3D3&startPage%3D468}}.</ref>
 
|  Formula = KH(IO<sub>3</sub>)<sub>2</sub>
 
|  Formula = KH(IO<sub>3</sub>)<sub>2</sub>
 
|  MolarMass = 389.91 g mol<sup>−1</sup>
 
|  MolarMass = 389.91 g mol<sup>−1</sup>
 
|  Appearance = white crystals
 
|  Appearance = white crystals
 +
|  Density = 4.17 g cm<sup>−3</sup>
 
|  MeltingPt = 105 °C ''decomp.''
 
|  MeltingPt = 105 °C ''decomp.''
 
|  Solubility = 1.33 g/100 ml (15 °C)
 
|  Solubility = 1.33 g/100 ml (15 °C)
 
   }}
 
   }}
 
| Section7 = {{Chembox Hazards
 
| Section7 = {{Chembox Hazards
|  Reference = <ref>{{GHS class NZ|id=1913|accessdate=2010-09-09}}. (potassium iodate)</ref><ref>{{GHS class NZ|id=12620|accessdate=2010-09-09}}. (iodic acid)</ref><ref group="Note">Hazards were assessed as for an equimolar mixture of [[potassium iodate]] and [[iodic acid]].</ref>
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|  Reference = {{#tag:ref|Hazards were assessed as for an equimolar mixture of [[potassium iodate]]<ref>{{GHS class NZ|id=1913|accessdate=2010-09-09}}. (potassium iodate)</ref> and [[iodic acid]].<ref>{{GHS class NZ|id=12620|accessdate=2010-09-09}}. (iodic acid)</ref>|group=Note}}
 
|  ExternalMSDS =  
 
|  ExternalMSDS =  
 
|  EUIndex = not listed
 
|  EUIndex = not listed
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===Preparation===
 
===Preparation===
Potassium biiodate is commercially available in analytical grade. However it may be conveniently prepared by simply mixing hot concentrated solutions of potassium iodate and iodic acid and allowing the potassium biiodate to crystallize. The crystals may be washed with absolute [[ethanol]] and dried in air.<ref name="Smith"/>
+
Potassium biiodate is commercially available in analytical grade. However it may be conveniently prepared by simply mixing hot concentrated solutions of potassium iodate and iodic acid and allowing the potassium biiodate to crystallize. The crystals may be recrysallized from hot water (3&nbsp;ml/g),<ref>{{Armarego&Chai|page=482}}.</ref> washed with absolute [[ethanol]] and dried in air.<ref name="Smith"/>
  
 
==Analytical use==
 
==Analytical use==
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===References===
 
===References===
{{reflist}}
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{{reflist|2}}
  
 
[[Category:Potassium compounds]]
 
[[Category:Potassium compounds]]
 
[[Category:Iodates]]
 
[[Category:Iodates]]
 +
[[Category:Acid–base titrations]]
 +
[[Category:Iodometry]]

Latest revision as of 19:53, 10 September 2010

Potassium biiodate
IUPAC name potassium µ-hydridobis(trioxidoiodate)(1−)
Other names potassium hydrogen iodate
Identifiers
InChI InChI=1/2HIO3.K/c2*2-1(3)4;/h2*(H,2,3,4);/q;;+1/p-1
InChIKey ACAYDTMSDROWHW-REWHXWOFAC
Standard InChI InChI=1S/2HIO3.K/c2*2-1(3)4;/h2*(H,2,3,4);/q;;+1/p-1
Standard InChIKey ACAYDTMSDROWHW-UHFFFAOYSA-M
CAS number [13455-24-8]
EC number 236-650-9
ChemSpider 2341255
Properties[1][2]
Chemical formula KH(IO3)2
Molar mass 389.91 g mol−1
Appearance white crystals
Density 4.17 g cm−3
Melting point

105 °C decomp.

Solubility in water 1.33 g/100 ml (15 °C)
Hazards[Note 1]
EU index number not listed
GHS pictograms Skin Corr. 1C, Eye Dam. 1Ox. Sol. 2Acute Tox. 4 (oral)
GHS signal word DANGER
GHS hazard statements H272, H302, H314, H318
GHS precautionary statements P210, P220, P221, P260, P264, P270, P280, P301+312, P301+330+331, P303+361+353, P363, P304+340, P310, P321
Flash point Non-flammable
Related compounds
Other compounds Potassium iodate
Iodic acid
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)

Potassium biiodate, KH(IO3)2, is a primary standard strong acid in analytical chemistry.[5][6]

Chemistry

The biiodate anion is a hydrogen-bonded species formed from the reaction of an iodate anion with undissociated iodic acid (pKa = 0.75).[7]

IO3 + HIO3 → [H(IO3)2]     Kc ≈ 4 dm3 mol−1

Hence, in dilute aqueous solutions, potassium biiodate can be considered to be a mixture of potassium iodate and iodic acid: however, it dissolves and recrystallizes coherently from water.[8]

Potassium biiodate loses water on heating to form a compound formulated as 2KIO3·I2O5: quantitative dehydration is described as rapid at 200 °C,[5] but takes three days at 105 °C.[8]

Preparation

Potassium biiodate is commercially available in analytical grade. However it may be conveniently prepared by simply mixing hot concentrated solutions of potassium iodate and iodic acid and allowing the potassium biiodate to crystallize. The crystals may be recrysallized from hot water (3 ml/g),[9] washed with absolute ethanol and dried in air.[8]

Analytical use

Potassium biiodate is used as a weighable primary standard for titrating solutions of bases. It has a much higher molar mass than benzoic acid and is slightly less susceptible to dehydration on oven drying than iodic acid.

It has also been used as a primary standard in iodometry, for standardizing solutions of sodium thiosulfate. The biiodate reacts with excess iodide in acidic solution to give a known amount of iodine, which can then be titrated against the thiosulfate solution.

[H(IO3)2] + 10 I + 11 H+ → 6 I2 + 6 H2O
I2 + 2 S2O32− → 2 I + S4O62−
1 [H(IO3)2] ≡ 12 S2O32−

Although it is used in several standard methods,[10] there is no practical advantage in using potassium biiodate over potassium iodate.[5]

Ferroelectricity

Potassium biiodate forms a ferroelectric phase below the Curie point of TC = 223(2) K.[11] The second-order phase transition appears to be associated with the ordering of the hydrogen bonds in the crystal structure.[12]

Notes and references

Notes

  1. Hazards were assessed as for an equimolar mixture of potassium iodate[3] and iodic acid.[4]

References

  1. CRC Handbook of Chemistry and Physics, 62nd ed.; Weast, Robert C., Ed.; CRC Press: Boca Raton, FL, 1981; p B-133. ISBN 0-8493-0462-8.
  2. Chan, Lilian Y. Y.; Einstein, F. W. B. The Crystal Structure of KIO3·HIO3. Can. J. Chem. 1971, 49, 468–76, <http://article.pubs.nrc-cnrc.gc.ca/ppv/RPViewDoc%3Fissn%3D1480-3291&volume%3D49&issue%3D3&startPage%3D468>.
  3. HSNO Chemical Classification Information Database, <http://www.ermanz.govt.nz/Chemicals/ChemicalDisplay.aspx?SubstanceID=1913> (accessed 9 September 2010), New Zealand Environmental Risk Management Authority. (potassium iodate)
  4. 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. (iodic acid)
  5. 5.0 5.1 5.2 Kolthoff, I. M.; van Berk, L. H. The Use of Potassium Bi-iodate as a Standard Substance in Alkalimetric and Iodimetric Titrations. J. Am. Chem. Soc. 1926, 48 (11), 2799–2801. DOI: 10.1021/ja01690a006.
  6. Processing KODAK Motion Picture Films, Module 4 – Potassium Biiodate; Kodak, <http://motion.kodak.com/motion/uploadedFiles/US_plugins_acrobat_en_motion_support_processing_h244_potBiiod.pdf>. (accessed 9 September 2010).
  7. Greenwood, Norman N.; Earnshaw, A. Chemistry of the Elements; Pergamon: Oxford, 1984; p 1010. ISBN 0-08-022057-6.
  8. 8.0 8.1 8.2 Smith, Sterling B. Ternary Systems. VIII. Potassium Iodate, Iodic Acid and Water. J. Am. Chem. Soc. 1947, 69 (10), 2285–86. DOI: 10.1021/ja01202a013.
  9. Armarego, W. L. F.; Chai, Christina Li Lin Purification of Laboratory Chemicals, 6th ed.; Butterworth-Heinemann: Oxford, 2009; p 482. ISBN 1856175677.
  10. Iodide – Titrimetric. In Methods for Chemical Analysis of Water and Wastes; Environmental Protection Agency: Washington, D.C., 1983. EPA-600/4-79-020, <http://www.ezkem.com/resources/articles/EPA_Methods/345_1.pdf>.
  11. Petrosyana, A. M.; Buscha, A. A.; Chechkina, V. V.; Volkova, A. F.; Venevtsev, Yu. N. Ferroelectric phase transition in potassium Bi-iodate. Ferroelectrics 1978, 21 (1), 525–26. DOI: 10.1080/00150197808237316.
  12. Barabash, A.; Baran, J.; Gavrilko, T.; Eshimov, K.; Puchkovskaya, G.; Ratajczak, H. Structure and dynamics of crystal α-modification of potassium biiodate. J. Mol. Struct. 1997, 404 (1–2), 187–91. DOI: 10.1016/S0022-2860(96)09380-5.