Potassium iodide

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Crystal structure
Structure of potassium iodide
__ K +      __ I -
Crystal system


Space group

Fm 3 m (No. 225)Template: room group / 225

Coordination numbers

K [6], I [6]

Surname Potassium iodide
other names
  • Potassium iodide
  • Iodine potash
Ratio formula AI
Brief description

white, odorless, crystalline solid

External identifiers / databases
CAS number 7681-11-0
EC number 231-659-4
ECHA InfoCard 100,028,782
PubChem 4875
ChemSpider 4709
DrugBank DB06715
Wikidata Q121874
Drug information
ATC code
Molar mass 166.00 g mol −1
Physical state



3.13 g cm −3

Melting point

723 ° C

boiling point

1325 ° C


good in water (1430 g l −1 at 20 ° C)

Refractive index


safety instructions
Please note the exemption from the labeling requirement for drugs, medical devices, cosmetics, food and animal feed
GHS labeling of hazardous substances
08 - Dangerous to health


H and P phrases H: 372
P: 314
Toxicological data

2779 mg kg −1 ( LD 50ratoral )

As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C

Potassium iodide is the white, readily soluble in water under strong cooling potassium - salt of hydriodic acid . Potassium iodide is used in the laboratory for the production of iodine potassium iodide solution ( Lugol's solution ). It is also used in the manufacture of silver iodide and in the production of pharmaceuticals. On the other hand, iodized table salt is a table salt enriched with sodium and potassium iodate (KIO 3 ).


Potassium hydroxide reacts with iodine to synthesize potassium iodide :

By glowing the iodide-iodate mixture with charcoal , the potassium iodate (KIO 3 ) can also be reduced to potassium iodide :

Very pure potassium iodide is obtained from potassium hydrogen carbonate with hydriodic acid .


The standard enthalpy of formation of potassium iodide is Δ H f 0  = −328 kJ / mol.

Potassium contains 0.0118% of the isotope 40 K, this provides 7343 Bq per kilogram of KI, of which 89.28% are beta radiation and 10.72% are gamma radiation with 1.46083 MeV.



In classical analytical chemistry, potassium iodide is used for the qualitative detection of lead as lead (II) iodide after that in the hydrochloric acid group has been separated. It is also required for quantitative analysis in iodometry as a titrator (standard solution) for the titration of copper .

Potassium iodide starch paper allows the unspecific detection of many dissolved or gaseous oxidizing agents. It is moistened to examine gases. Oxidizing agents oxidize the iodide to iodine, which with starch results in the well-known dark intercalation compound. Among other things, the following are recorded: ozone , nitrogen oxides , hydrogen peroxide , organic peroxides , chlorine , bromine .

The potassium iodide method is used for the quantitative determination of ozone in the outside air: In aqueous solution, ozone reacts with potassium iodide, releasing iodine and O 2 . The extinction of the iodine solution is a measure of the ozone concentration in the sample air that has passed through the potassium iodide solution.

Radiation protection

Potassium iodide is also important in radiation protection . In the form of tablets (colloquially known as "iodine tablets"), potassium iodide is given as a preventative measure in the event of accidents in nuclear facilities. The iodine blockade caused by the potassium iodide leads to a reduction in the absorption of radioactive iodine ( 131 I) in the thyroid gland by a factor of 90 and more. The iodine blockage should take place before the radioactive iodine is absorbed, but no later than two hours afterwards. If taken later, potassium iodide can still shorten the time the radioiodine stays in the body. However, the first application should not take place later than one day after the ingestion of radioactive iodine, otherwise its excretion is delayed and the time it remains in the body is increased.

In Switzerland, potassium iodide is distributed preventively to the population within 50 kilometers of nuclear power plants . In the event of an accident, the Swiss Federal Office of Public Health orders potassium iodide tablets to be taken via siren alarms and radio messages.

Potassium iodide tablets are stocked in schools, pharmacies, general practitioners and hospitals throughout Austria. If there is a specific order from the Ministry of Health, the delivery is free.

In Germany, iodine tablets in the required dosage can be obtained from pharmacies without a prescription. However, a clear distinction must be made between iodide tablets (dosage mostly 100–200 µg iodide), which are used for iodine deficiency and thyroid diseases, and special emergency tablets, which contain the required amount of active ingredient (approx. 50 mg iodide). Only the emergency tablets are suitable for iodine blockade , as they contain the necessary amount of iodide for emergency use. In 2004, German energy providers ordered 137 million tablets for the accident. How and when these tablets are dispensed is the responsibility of the country . The potassium iodide tablets are usually kept in municipalities in the vicinity of nuclear facilities in order to be distributed to the population in the event of a disaster.

Depending on the expected dose, you should take potassium iodide tablets by order of the authorities:

  • Children and young people
  • Pregnant and breastfeeding women
  • Adults up to 45 years

For the group of over 45-year-olds, the intake of potassium iodide tablets is generally not considered, since the risk of triggering an overactive thyroid is generally assessed to be greater than the positive effect of protection against radiation exposure. The reason for this is the increased sensitivity of this age group to iodine, which in their childhood and adolescence - before the introduction of table salt iodination in 1963 - sometimes suffered from iodine deficiency. This increased sensitivity does not exist in the other age groups. The IPPNW also recommends the use of iodine blockade in those over 40 years of age.

After local experiments, Switzerland introduced the first nationwide salt iodination in 1922 and thus assumed a pioneering role. Since then, the Swiss Rhine Saltworks have been adding potassium iodide to the table salt on behalf of the authorities.

According to the recommendations of the World Health Organization, an organ dose of 50 millisieverts for children up to 12 years of age and pregnant women and 250 millisieverts for adolescents and adults from 13 to 40 years of age apply as intervention guide values  .

Potassium iodide tablets are not universally effective "radiation protection tablets". When taken in a timely manner, they only protect the thyroid gland from radioiodine that enters the body through breathing or food. They do not protect against other radioactive substances and not against direct radiation that affects the body from outside. Additional protective measures (e.g. temporary stay in closed rooms, food control, decontamination ) are by no means superfluous.

Iodine tablets should only be taken on the instructions of the authorities, as they can have severe side effects in this high dosage , namely palpitations , sweating, tremors, weight loss, restlessness and indigestion.

Web links

Individual evidence

  1. Entry on POTASSIUM IODIDE in the CosIng database of the EU Commission, accessed on February 16, 2020.
  2. a b c d e f g Entry on potassium iodide in the GESTIS substance database of the IFA , accessed on January 8, 2018(JavaScript required) .
  3. David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Index of Refraction of Inorganic Crystals, pp. 10-246.
  4. Data sheet potassium iodide (PDF) from Merck , accessed on February 1, 2013.
  5. G. Brauer (Ed.): Handbook of Preparative Inorganic Chemistry. 2nd Edition. vol. 1, Academic Press, 1963, p. 290.
  6. ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 101st edition. Walter de Gruyter, Berlin 1995, ISBN 3-11-012641-9 , p. 1170.
  7. VDI 2468 sheet 1: 1978-05 measurement of gaseous immissions; Measuring ozone and peroxide concentration; Manual photometric method; Potassium iodide method (basic method). VDI Verlag, Düsseldorf, p. 2.
  8. ^ Franz Joseph Dreyhaupt (ed.): VDI-Lexikon Umwelttechnik. VDI-Verlag, Düsseldorf 1994, ISBN 3-18-400891-6 , p. 663.
  9. ^ H. Schicha: Iodine blockade of the thyroid gland. In: Federal Minister for the Environment, Nature Conservation and Nuclear Safety (Ed.): Medical measures in the event of radiation accidents. (= Publications of the Radiation Protection Commission. Volume 27). Gustav Fischer Verlag, Stuttgart / Jena / New York 1994, pp. 187-205.
  10. ^ Chr. Reiners: Prophylaxis of radiation-induced thyroid carcinomas in children after the Chernobyl reactor disaster. In: Nuclear Medicine. 33, 1994, pp. 229-234.
  11. The iodine tablet for your protection. - Homepage at www.kaliumiodid.ch ; As of June 5, 2008.
  12. Katharina Lehner: Atomic super-GAU: What do communities have to do in an emergency? Austrian association of municipalities. March 22, 2011, accessed October 4, 2012.
  13. Frequently asked questions | Federal Environment Ministry. Retrieved April 13, 2017 .
  14. Potassium iodide tablets information sheet. (PDF) Retrieved April 13, 2017 .
  15. a b c d Taking iodine tablets. (PDF) Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety, p. 6 below , accessed on April 13, 2017 .
  16. German energy suppliers buy 137 million iodine pills for residents of nuclear power plants. In: Spiegel online . January 10, 2004.
  17. ^ Iodine blockade of the thyroid in nuclear accidents ( Memento from January 15, 2012 in the Internet Archive ) - Document at the Commission on Radiological Protection ; As of June 5, 2008.
  18. PPNW recommendations for iodine tablets in the event of a nuclear accident (iodine blockade) ( Memento from June 6, 2014 in the Internet Archive ) - document at the IPPNW ; As of March 15, 2011.
  19. ^ Iodine in salt - the goiter on the collar. ( Memento from May 18, 2015 in the Internet Archive )
  20. World Health Organization (WHO): Guidelines for Iodine Prophylaxis following Nuclear Accidents. Published on behalf of the WHO Regional Office for Europe by FADL, Copenhagen, 1989.
  21. Radiation protection advice, what to do in the event of nuclear power plant accidents / instructions for preventive measures. Federal Ministry of the Interior, Department for Civil Protection, Herrengasse 7, 1014 Vienna. Sixth, revised and expanded edition. June 2001.
  22. Nuclear accident in Japan: Do not take iodine without official advice. ( Memento from September 4, 2012 in the web archive archive.today )
  23. rp-online.de March 17, 2011 .