Potassium iodide
1014366
226130074
2008-07-16T23:14:17Z
Plantsurfer
1750837
/* Uses */ occasionally
{{Chembox new
| Name = Potassium iodide
| ImageFile = Potassium iodide.jpg
| ImageFile1 = Potassium-iodide-3D-ionic.png
| IUPACName = Potassium iodide
| OtherNames = Kalium iodide,<br />knollide, potide
| Section1 = {{Chembox Identifiers
| CASNo = 7681-11-0
| RTECS = TT2975000
}}
| Section2 = {{Chembox Properties
| Formula = KI
| MolarMass = 166.00 g/mol
| Appearance = white crystalline solid
| Density = 3.13 g/cm<sup>3</sup>, solid
| Solubility = 128 g/100 ml (6 °C)
| MeltingPt = 681 °C (954 K)
| BoilingPt = 1330 °C (1603 K)
| pKa =
}}
| Section3 = {{Chembox Structure
| Coordination =
| CrystalStruct =
| Dipole =
}}
| Section7 = {{Chembox Hazards
| ExternalMSDS = [http://www.jtbaker.com/msds/englishhtml/p5906.htm External MSDS]
| MainHazards = Slightly hazardous
| NFPA-H = 1
| NFPA-F =
| NFPA-R =
| RPhrases = {{R36}}, {{R38}}, {{R42}}-{{R43}}, {{R61}}
| SPhrases = {{S26}}, {{S36}}-{{S37}}, {{S39}}, {{S45}}
}}
| Section8 = {{Chembox Related
| OtherAnions = [[potassium bromide]]<br />[[potassium chloride]]
| OtherCations = [[lithium iodide]]<br />[[sodium iodide]]<br />[[rubidium iodide]]<br />[[caesium iodide]]
}}
}}
'''Potassium iodide''' is a white [[crystal]]line [[salt]] with [[chemical formula]] {{potassium}}{{iodine}}, used in [[photography]] and radiation treatment. It finds widespread application as an iodide source because it is less [[hygroscopic]] than [[sodium iodide]], making it easier to work with. KI can turn yellow upon heating in air or upon standing in moist air for long periods, because of [[oxidation]] of the [[iodide]] to [[iodine]].
== Chemical properties ==
'''Potassium iodide''' behaves as a simple [[ion]]ic [[salt]], K<sup>+</sup>I<sup>−</sup>. Since the [[iodide]] ion is a mild [[Redox|reducing agent]], I<sup>−</sup> is easily oxidised to [[iodine|I<sub>2</sub>]] by powerful [[redox|oxidising agents]] such as [[chlorine]]:
:2 KI([[aqueous|aq]]) + [[Chlorine|Cl<sub>2</sub>]](aq) → 2 [[Potassium chloride|KCl]] + [[Iodine|I<sub>2</sub>]](aq)
Even air will oxidize iodide as evidenced by the observation of a purple extract when KI is rinsed with [[dichloromethane]]. Under acidic conditions, KI is oxidised even more easily, due to the formation of [[hydroiodic acid]] (HI), which is a powerful reducing agent.<ref>N. N. Greenwood, A. Earnshaw, ''Chemistry of the Elements'', Pergamon Press, Oxford, UK, 1984</ref><ref>''Handbook of Chemistry and Physics'', 71st edition, CRC Press, Ann Arbor, Michigan, 1990</ref><ref>''The Merck Index'', 7th edition, Merck & Co., Rahway, New Jersey, 1960</ref><ref>H. Nechamkin, ''The Chemistry of the Elements'', McGraw-Hill, New York, 1968</ref>
KI forms [[triiodide|I<sub>3</sub><sup>−</sup>]] when combined with elemental [[iodine]].
:KI(aq) + [[Iodine|I<sub>2</sub>]]([[solid|s]]) → KI<sub>3</sub>(aq)
Unlike I<sub>2</sub>, I<sub>3</sub><sup>−</sup> salts can be highly water-soluble. <!--the following statement is untrue or at least imprecise and confusing, because I2 no longer exists in the presence of I−: "this reaction is frequently used to render I<sub>2</sub> more soluble in water"--> I<sub>2</sub> and I<sub>3</sub><sup>−</sup> have virtually identical redox potentials (0.535 and 0.536 V vs NHE, respectively), i.e. they are both mild oxidants relative to H<sub>2</sub>. Therefore, this reaction allows the [[iodine]] to be used in aqueous solutions for [[redox]] [[titration]]s.
Potassium iodide also serves in some organic reactions as a source of iodide ion (see "uses" below).
== Physical Properties ==
It occurs as odourless, colourless, transparent or somewhat opaque crystals or white granular powder. It is slightly hygroscopic, the taste is saline and slightly bitter.
On long exposure to air, it becomes yellow due to the liberation of iodine and small quantities of iodate may be formed.
== Uses ==
Potassium iodide is used in [[photography]], in the preparation of [[silver(I) iodide]] for high speed [[photographic film]]:
:KI([[aqueous|aq]]) + [[Silver nitrate|AgNO<sub>3</sub>]]([[aqueous|aq]]) → [[Silver iodide|AgI]]([[solid|s]]) + [[Potassium nitrate|KNO<sub>3</sub>]]([[aqueous|aq]])
Potassium iodide is also added to [[sodium chloride|table salt]] in small quantities to make it "iodized". In a saturated solution, it is also used as an [[expectorant]] to treat lung congestion.
KI is often used as a source of [[iodide]] ion in [[organic synthesis]]. A useful application is in the preparation of aryl iodides from [[arenediazonium salts]].<ref>L. G. Wade, ''Organic Chemistry'', 5th ed., pp. 871-2, Prentice Hall, Upper Saddle RIver, New Jersey, 2003</ref><ref>J. March, ''Advanced Organic Chemistry'', 4th ed., pp. 670-1, Wiley, New York, 1992</ref> For example:
[[Image:KI Sandmeyer.png|400px]]
KI is also used as a [[fluorescence quenching]] agent in biomedical research because of collisional quenching by its iodide ion.
A saturated solution of potassium iodide (abbreviated [[SSKI]]) is also used as treatment for [[sporotrichosis]], a fungal infection, and also as an expectorant.
KI has been used, along with elemental iodine, to make [[Lugol's solution]], which uses iodide to improve the solubility of elemental iodine in water. Elemental iodine is much more toxic than KI, so such solutions are ordinarily not swallowed, but are used as water disinfectants, for topical uses as local disinfectants, and occasionally as a gargle-rinse for treating sore throat.
In aqueous solution with elemental iodine, similar solutions to Lugol's act as a gold etchants and will attack and dissolve gold surfaces. This attack on gold by free halogen is similar to that by free chlorine produced in [[aqua regia]].
==Radiation protection==
Following the [[Chernobyl disaster|Chernobyl nuclear reactor disaster]] in April, [[1986]], a saturated solution of potassium iodide ([[SSKI]]) was administered to 10.5 million children and 7 million adults in [[Poland]]<ref>[http://www.fda.gov/cder/guidance/4825fnl.htm] US FDA, "Potassium Iodide as a Thyroid Blocking Agent in Radiation Emergencies," U.S. Department of Health and Human Services Food and Drug Administration Center for Drug Evaluation and Research (CDER); December, 2001.</ref> as a prophylactic measure against accumulation of radioactive [[iodine-131]] in the [[thyroid]].
Potassium iodide was also FDA approved in 1982 to protect the [[thyroid]] from [[radioiodine|radioactive iodine]]. In the event of an accident or attack at a [[nuclear power plant]], or fallout from a nuclear bomb, several volatile fission product radionuclides may be released. [[Iodine-131|<sup>131</sup>I]] is a common fission by-product and is particularly dangerous as the body concentrates it only in the thyroid gland which may lead to thyroid cancer. By saturating the body with a source of stable iodine prior to exposure, any radioactive <sup>131</sup>I inhaled or ingested becomes the excess in the blood system and is excreted through the kidneys. Potassium iodide cannot protect against any other causes of [[radiation poisoning]], however, nor can it provide any degree of protection against a [[dirty bomb]] unless the bomb happens to contain a significant amount of [[iodine-131|radioactive iodine]]. In case of a [[Nuclear fallout|nuclear emergency]], ''[[iodine]]'' used for the cleaning of wounds should '''not''' be ingested, as it is [[poisonous]]. Only 3 brands of potassium iodide have been tested and approved for use by the [[FDA]] as a thyroid blocking agent during exposure to radioactive iodine (Iosat, ThyroShield and Thyro-safe) and hence [[potassium iodate]] is not approved in the U.S. for this purpose.
{| class="wikitable"
|+ Recommended Dosage for Radiological Emergencies involving radioactive iodine<ref>''Guidelines for Iodine Prophylaxis following Nuclear Accidents'', [[World Health Organization]], Update 1999</ref>
! Age
! KI in mg
|-
| Over 12 years old
| 130
|-
| 3 - 12 years old
| 65
|-
| 1 - 36 months old
| 32
|-
| < 1 month old
| 16
|}
See [[fission products]] and the external links for more details.
== Precautions ==
Mild irritant, wear gloves. Chronic overexposure can have adverse effects on the thyroid.
== References ==
{{reflist}}
==External links==
* {{ATC|R05|CA02}}
* [http://www.who.int/ionizing_radiation/pub_meet/en/Iodine_Prophylaxis_guide.pdf World Health Organization's guidelines for iodine prophylaxis following a nuclear accident]
*[http://www.nukepills.com/potassium-iodide.htm Nukepills.com] Potassium Iodide Information
{{Antidotes}}
[[Category:Potassium compounds]]
[[Category:Metal halides]]
[[Category:Iodides]]
[[Category:Disaster preparedness]]
[[Category:Radiobiology]]
[[Category:Photographic chemicals]]
[[Category:Food additives]]
[[Category:Expectorants]]
[[bs:Kalijum jodid]]
[[bg:Калиев йодид]]
[[ca:Iodur de potassi]]
[[de:Kaliumiodid]]
[[es:Yoduro de potasio]]
[[it:Ioduro di potassio]]
[[lv:Kālija jodīds]]
[[hu:Kálium-jodid]]
[[nl:Kaliumjodide]]
[[ja:ヨウ化カリウム]]
[[nn:Kaliumjodid]]
[[pl:Jodek potasu]]
[[pt:Iodeto de potássio]]
[[ru:Иодид калия]]
[[sr:Калијум јодид]]
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[[zh:碘化钾]]