Difference between revisions of "Potassium biiodate"
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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. | 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(IO<sub>3</sub>)<sub>2</sub>]<sup>−</sup> + 10 I<sup>−</sup> + 11 H<sup>+</sup> → 6 I<sub>2</sub> + 6 H<sub>2</sub>O | :[H(IO<sub>3</sub>)<sub>2</sub>]<sup>−</sup> + 10 I<sup>−</sup> + 11 H<sup>+</sup> → 6 I<sub>2</sub> + 6 H<sub>2</sub>O | ||
| + | :I<sub>2</sub> + 2 S<sub>2</sub>O<sub>3</sub><sup>2−</sup> → 2 I<sup>−</sup> + S<sub>4</sub>O<sub>6</sub><sup>2−</sup> | ||
| + | ::1 [H(IO<sub>3</sub>)<sub>2</sub>]<sup>−</sup> ≡ 12 S<sub>2</sub>O<sub>3</sub><sup>2−</sup> | ||
Although it is used in several standard methods,<ref>{{citation | contribution = Iodide – Titrimetric | title = Methods for Chemical Analysis of Water and Wastes | publisher = Environmental Protection Agency | location = Washington, D.C. | year = 1983 | id = EPA-600/4-79-020 | url = http://www.ezkem.com/resources/articles/EPA_Methods/345_1.pdf}}.</ref> there is no practical advantage in using potassium biiodate over potassium iodate.<ref name="Kolthoff"/> | Although it is used in several standard methods,<ref>{{citation | contribution = Iodide – Titrimetric | title = Methods for Chemical Analysis of Water and Wastes | publisher = Environmental Protection Agency | location = Washington, D.C. | year = 1983 | id = EPA-600/4-79-020 | url = http://www.ezkem.com/resources/articles/EPA_Methods/345_1.pdf}}.</ref> there is no practical advantage in using potassium biiodate over potassium iodate.<ref name="Kolthoff"/> | ||
Revision as of 08:30, 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 | [] |
| EC number | |
| ChemSpider | |
| Properties[1] | |
| Chemical formula | KH(IO3)2 |
| Molar mass | 389.91 g mol−1 |
| Appearance | white crystals |
| Melting point |
105 °C decomp. |
| Solubility in water | 1.33 g/100 ml (15 °C) |
| Hazards[2][3][Note 1] | |
| EU index number | not listed |
| GHS pictograms |   
|
| 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.[4][5]
Contents
Chemistry
The biiodate anion is a hydrogen-bonded species formed from the reaction of an iodate anion with undissociated iodic acid (pKa = 0.75).[6]
- IO−3 + 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.[7]
Potassium biiodate loses water on heating to form a compound formulated as 2KIO3·I2O5: quantitative dehydration is described as rapid at 200 °C,[4] but takes three days at 105 °C.[7]
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.[7]
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,[8] there is no practical advantage in using potassium biiodate over potassium iodate.[4]
Ferroelectricity
Potassium biiodate forms a ferroelectric phase below the Curie point of TC = 223(2) K.[9] The second-order phase transition appears to be associated with the ordering of the hydrogen bonds in the crystal structure.[10]
Notes and references
Notes
- ↑ Hazards were assessed as for an equimolar mixture of potassium iodate and iodic acid.
References
- ↑ 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.
- ↑ 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)
- ↑ 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)
- ↑ 4.0 4.1 4.2 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.
- ↑ 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).
- ↑ Greenwood, Norman N.; Earnshaw, A. Chemistry of the Elements; Pergamon: Oxford, 1984; p 1010. ISBN 0-08-022057-6.
- ↑ 7.0 7.1 7.2 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.
- ↑ 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>.
- ↑ 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.
- ↑ 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.
