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Potassium iodide

Potassium iodide
Image:Potassium iodide.jpg
Systematic name Potassium iodide
Other names Kalium iodide,
knollide, potide
Molecular formula KI
Molar mass 166.00 g/mol
Appearance white crystalline solid
CAS number [8781-11-0]
Densityand phase 3.13 g/cm3, solid
Solubilityin water 128 g/100 ml (6 C)
Melting point 680 C (953 K)
Boiling point 1330 C (1600 K)
Acidity(pKa)  ?
Basicity(pKb)  ?
Molecular shape  ?
Coordination geometry  ?
Crystal structure  ?
Dipole moment  ? D
MSDS External MSDS
Main hazards Slightly hazardous
NFPA 704 Image:Nfpa h1.pngImage:Nfpa f0.pngImage:Nfpa r0.png
R/S statement R: 36, 38, 42-43, 61
S: 26, 36-37, 39, 45
RTECSnumber TT2975000
Supplementary data page
Structure & properties n, εr, etc.
Thermodynamic data Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
Related compounds
Other anions potassium bromide
potassium chloride
Other cations sodium iodide
rubidium iodide
calcium iodide
Related compounds  ?
Except where noted otherwise, data are given for
materials in their standard state (at 25°C, 100 kPa)
Infobox disclaimer and references

Potassium iodide is a white crystallinesaltwith chemical formulaKI, used in photographyand 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 iodideto iodine.


  • 1 Chemical properties
  • 2 Preparation
  • 3 Uses
  • 4 Role of potassium iodide in radiological emergency preparedness
  • 5 Precautions
  • 6 Suppliers/Manufacturers
  • 7 References

Chemical properties

Potassium iodide behaves as a simple ionicsalt, K+I-. Since iodideion is a mild reducing agent, KI is easily oxidised to iodineby oxidising agentssuch as chlorine:

2 KI(aq) + Cl2(aq) → 2 KCl + I2(aq)

If dichloromethaneis present, the purple colour of elemental iodine may be seen in the organic phase. Under acidic conditions, KI is oxidised even more easily, due to the formation of hydroiodic acid(HI), which is a powerful reducing agent.

KI also forms a complex ion I3- when combined with elemental iodine, and in fact this reaction is frequently used to render I2 more soluble in water:

KI(aq) + I2(s) → KI3(aq)

The reaction is slightly reversible, allowing the iodineto be used in aqueous solutions for redoxtitrations.

Potassium iodide also reacts in some organic reactions as a source of iodide ion (see "uses" below).


Potassium iodide may be prepared by the reaction of a potassium base with hydroiodic acid, for example:

HI + KHCO3 → KI + H2O(l) + CO2(g)

Alternatively iron(II) iodide, prepared using scrap ironand iodine(made from iodide rich brinesor from Chile saltpeter, can be treated with potassium carbonate:

FeI2 + K2CO3 → 2 KI + FeCO3


Potassium iodide is used in photography, in the preparation of silver(I) iodidefor high speed photographic film:

KI(aq) + AgNO3(aq) → AgI(s) + KNO3(aq)

Potassium iodide is also added to table saltin small quantities to make it "iodized". In a saturated solution, it is also used as an expectorantto treat lung congestion.

KI is often used as a source of iodideion in organic synthesis. A useful application is in the preparation of aryl iodides from arenediazonium salts[5], for example:

Image:KI Sandmeyer.png

Saturated solution of potassium iodide is also used as treatment for sporotrichosis, a fungal infection.

Role of potassium iodide in radiological emergency preparedness

Potassium iodide may also be used to protect the thyroidfrom radioactive iodinein the event of an accident or terrorist attack at a nuclear power plant, or other nuclear attack, especially where a nuclear reactoris breached and the volatile radionuclides, which contain significant amount of 131I, are released into the environment. Radioiodine is a particularly dangerous radionuclide because the body concentrates it in the thyroid gland. Potassium iodide cannot protect against other causes of radiation poisoning, however, nor can it provide any degree of protection against a dirty bombunless the bomb happens to contain a significant amount of radioactive iodine.

The purpose of radiological emergency preparedness is to protect people from the effects of radiation exposure after an accident at a nuclear power plant. Evacuation is the most effective protective measure in the event of a radiological emergency because it protects the whole body (including the thyroid gland and other organs) from all radionuclides and all exposure pathways. However, in situations when evacuation is not feasible and in-place sheltering is substituted as an effective protective action, administering potassium iodide reduces the effects of radio iodine by 99%, and is a prudent, inexpensive supplement to sheltering. Potassium iodide protects the thyroid gland against internal uptake of radioiodines that may be released in the event of a nuclear reactor accident or from fallout. When potassium iodide is ingested, it is taken up by the thyroid gland. In the proper dosage, and taken at the appropriate time, it will effectively saturate the thyroid gland in such a way that inhaled or ingested radioactive iodines will not be accumulated in the thyroid gland. The risk of thyroid effects is reduced. Such thyroid effects resulting from radioiodine uptakes due to inhalation or ingestion, or both, could result in acute, chronic, and delayed effects. Acute effects from high doses include thyroiditis, while chronic and delayed effects include hypothyroidism, thyroid nodules, and thyroid cancer. The FDAhas approved potassium iodide as an over-the-counter medication. As with any medication, individuals should check with their doctor or pharmacist before using it.

A low-cost alternative to commercially available iodine pills is a saturated solutionof potassium iodide. It usually possible to obtain several thousand doses for prices near US$ 0.01/dose. Long term storage of KI is normally in the form of reagent grade crystals, which are convenient and available commercially. The purity is superior to "pharmacologic grade". Its concentration depends only on temperature, which is easy to determine, and the required dose is easily administered by measuring the required volume of the liquid. At room temperature, the U.S. standard adult radiological protective dose of 130mg is four drops of a saturated solution. A baby's dose is 65mg, or two drops. It's normally administered in a ball of bread, because it tastes incredibly bad. Use is contraindicated in individual known to be allergic to iodine. (see chap 13, Kearney, below)


Irritant. Wear gloves and goggles. Chronic oxerexposure can have adverse effects on the thyroid.


  • VWR
  • Strem
  • Alfa
  • Sigma-Aldrich
  • Fisher
  • Iosat-ThyroShield Potassium Iodide


  1. N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, Pergamon Press, Oxford, UK, 1984.
  2. Handbook of Chemistry and Physics, 71st edition, CRC Press, Ann Arbor, Michigan, 1990.
  3. The Merck Index, 7th edition, Merck & Co., Rahway, New Jersey, 1960.
  4. H. Nechamkin, The Chemistry of the Elements, McGraw-Hill, New York, 1968.
  5. (a) L. G. Wade, Organic Chemistry, 5th ed., pp. 871-2, Prentice Hall, Upper Saddle RIver, New Jersey, 2003. (b) J. March, Advanced Organic Chemistry, 4th ed., pp. 670-1, Wiley, New York, 1992.
  6. Cresson Kearny, Nuclear War Survival Skills, available on line at Oregon Institute of Science and Medicine, created with the permission of the author. The information on KI is near the end of chapter 13. This manual has proven technical info on expedient fallout shelters, and assorted shelter system needs that can be created from common household items. OISM also offers free downloads of other civil defense and shelter information as well.de:Kaliumiodid

ja:ヨウ化カリウム pl:Jodek potasu zh:碘化钾 sr:??????? ?????

This article is licensed under the GNU Free Documentation License.
It uses material from the http://en.wikipedia.org/wiki/Potassium+iodide Wikipedia article Potassium iodide.

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