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Potassium iodide
CAS number 7681-11-0 Yes check.svgY
PubChem 4875
RTECS number TT2975000
Molecular formula KI
Molar mass 166.0028 g/mol
Appearance white crystalline solid
Density 3.123 g/cm3
Melting point

681 °C, 954 K, 1258 °F

Boiling point

1330 °C, 1603 K, 2426 °F

Solubility in water 128 g/100 ml (0 °C)
140 g/100 mL (20 °C)
176 g/100 mL (60°C)
206 g/100 mL (100°C)
Solubility 2 g/100 mL (ethanol)
soluble in acetone
slightly soluble in ether, ammonia
MSDS External MSDS
EU Index Not listed
NFPA 704
NFPA 704.svg
Related compounds
Other anions Potassium fluoride
Potassium chloride
Potassium bromide
Other cations Lithium iodide
Sodium iodide
Rubidium iodide
Caesium iodide
 Yes check.svgY (what is this?)  (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Potassium iodide is an inorganic compound with formula KI. This white salt is the most commercially significant iodide compound, with approximately 37,000 tons produced in 1985. It is less hygroscopic than sodium iodide, making it easier to work with. Aged and impure samples are yellow because of oxidation of the iodide to iodine.[1]

4 NaI + 2 CO2 + O2 → 2 Na2CO3 + 2 I2

Potassium iodide is used medicinally in tablets, usually containing 130 mg of KI and 100 mg iodine (as iodide). Potassium iodide may also be administered as a "saturated solution of potassium iodide" (SSKI) which in the U.S.P. generic formulation contains 1000 mg of KI per mL. This represents 333 mg KI and about 250 mg iodide, I - in a typical adult dose of 5 drops, assumed to be ⅓ mL. [2]. Because SSKI is a viscous liquid, it is normally assumed to contain 15 drops/milliliter, not 20 drops/milliliter as is often assumed for water.[3] Thus, each drop of SSKI is assumed to contain about 50 mg iodine as iodide, I -. Two (2) drops of SSKI solution is equivalent to one 130 mg KI tablet (100 mg iodide).


Structure, production, properties

Potassium iodide is ionic, K+I. It crystallises in the sodium chloride structure. It is produced industrially by treating KOH with iodine.[1]


[['===Inorganic chemistry=

Since the iodide ion is a mild reducing agent, I is easily oxidised to I2 by powerful oxidising agents such as chlorine:

2 KI(aq) + Cl2(aq) → 2 KCl + I2(aq)

This reaction is employed in the isolation of iodine from natural sources. Air will oxidize iodide, as evidenced by the observation of a purple extract when aged samples of KI are rinsed with dichloromethane. As formed under acidic conditions, hydroiodic acid (HI) is a stronger reducing agent.[4][5][6]

Like other iodide salts, KI forms I3 when combined with elemental iodine.

KI(aq) + I2(s) → KI3(aq)

Unlike I2, I3 salts can be highly water-soluble. Through this reaction iodine is used in redox titrations. Aqueous KI3, "Lugol's solution," are used as disinfectants and as etchants for gold surfaces.

Potassium iodide is the precursor to silver(I) iodide, which is used for high speed photographic film:

KI(aq) + AgNO3(aq) → AgI(s) + KNO3(aq)']] ==]]

Organic chemistry

KI serves as a source of iodide in organic synthesis. A useful application is in the preparation of aryl iodides from arenediazonium salts.[7][8] For example:

KI Sandmeyer.png


The major uses of KI include use as a nutritional supplement in animal feeds and also the human diet. For the latter, it is the most common additive used to "iodize" table salt (a public health measure to prevent iodine deficiency in populations which get little seafood). Potassium iodide is also used as a pharmaceutical (see following section).

KI is a precursor to silver iodide (AgI) an important chemical in photography. KI is a component in some disinfectants and hair treatment hair chemicals. KI is also used as a fluorescence quenching agent in biomedical research, an application that takes advantage of collisional quenching of fluoresent substances by the iodide ion.


Since potassium iodide is highly soluble in water, a saturated solution of potassium iodide, abbreviated SSKI, contains 1 gram (1000 mg) KI per milliliter (mL) of solution. This is less than 100% by weight, because SSKI is significantly more dense than pure water. Because KI is about 76.4% iodide by weight, SSKI contains about 764 mg iodide per mL, which is usually rounded to 750 mg/mL for convenience (50 mg iodide per drop, at 15 drops per mL typical of viscous liquids like SSKI).

Saturated solutions of potassium iodide can be an emergency treatment for hyperthyroidism (so-called thyroid storm), as high amounts of iodide temporarily suppress secretion of thyroxine from the thyroid gland.[citation needed] The dose typically begins with a loading dose, then 1/3 mL (5 drops = 250 mg iodide) SSKI, three times per day.

Iodide solutions made from a few drops of SSKI added to drinks have also been used as expectorants to increase the water content of respiratory secretions and encourage effective coughing.[citation needed]

SSKI may be used in radioiodine-contamination emergencies (i.e., nuclear accidents) to "block" the thyroid's uptake of radioiodine (this is not the same as blocking the thyroid's release of thyroid hormone). The dose is smaller: 130 mg KI per day (100 mg iodide) which represents 2 drops of SSKI solution per day, for an adult.

SSKI has been proposed as a topical treatment for sporotrichosis, but no trials have been conducted to determine the efficacy or side effects of such treatment. [9]

Radiation protection

Following the 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[10] as a prophylactic measure against accumulation of radioactive iodine-131 in the thyroid gland.

Potassium iodide was also approved in 1982 by the US FDA to protect the thyroid glands from 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. 131I is a common fission by-product and is particularly dangerous as the body concentrates it in the thyroid gland, which may lead to thyroid cancer. By saturating the body with a source of stable iodide prior to exposure, inhaled or ingested 131I tends to be excreted. Potassium iodide cannot protect against any other causes of radiation poisoning, nor can it provide any degree of protection against dirty bombs that produce radionuclides other than isotopes of iodine.

Recommended Dosage for Radiological Emergencies involving radioactive iodine[11]
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.

Potassium iodide’s (KI) value as a radiation protective (thyroid blocking) agent was demonstrated at the time of the Chernobyl nuclear accident when Soviet authorities distributed it in a 30 km zone around the plant. The purpose was to protect residents from radioactive iodine, a highly carcinogenic material found in nuclear reactors which had been released by the damaged reactor. Only a limited amount of KI was available, but those who received it were protected. Later, the US Nuclear Regulatory Commission (NRC) reported, “thousands of measurements of I-131 (radioactive iodine) activity…suggest that the observed levels were lower than would have been expected had this prophylactic measure not been taken. The use of KI…was credited with permissible iodine content in 97% of the evacuees tested.” [12]

Poland, 300 miles from Chernobyl, also distributed KI to protect its population. Approximately 18 million doses were distributed, with follow-up studies showing no known thyroid cancer among KI recipients. [13] With the passage of time, people living in irradiated areas where KI was not available have developed thyroid cancer at epidemic levels, which is why the US Food and Drug Administration (FDA) reported “The data clearly demonstrate the risks of thyroid radiation…KI can be used [to] provide safe and effective protection against thyroid cancer caused by irradiation. [14]

Chernobyl also demonstrated that the need to protect the thyroid from radiation was greater than expected. Within ten years of the accident, it became clear that thyroid damage caused by released radioactive iodine was virtually the only adverse health effect that could be measured. As reported by the NRC, studies after the accident showed that “As of 1996, except for thyroid cancer, there has been no confirmed increase in the rates of other cancers, including leukemia, among the…public, that have been attributed to releases from the accident.” [15]

But equally important to the question of KI is the fact that radiation releases are not “local” events. Researchers at the World Health Organization accurately located and counted the cancer victims from Chernobyl and were startled to find that “the increase in incidence [of thyroid cancer] has been documented up to 500 km from the accident site…significant doses from radioactive iodine can occur hundreds of kilometers from the site, beyond emergency planning zones." [16] Consequently, far more people than anticipated were affected by the radiation, which caused the United Nations to report in 2002 that “The number of people with thyroid cancer…has exceeded expectations. Over 11,000 cases have already been reported.” [17]

These findings were consistent with studies of the effects of previous radiation releases. In 1945, millions of Japanese were exposed to radiation from nuclear weapons, and the effects can still be measured. Today, nearly half (44.8%) the survivors of Nagasaki studied have identifiable thyroid disease, with the American Medical Association reporting “it is remarkable that a biological effect from a single brief environmental exposure nearly 60 years in the past is still present and can be detected.” [18]

These events, as well as the development of thyroid cancer among residents in the North Pacific from radioactive fallout following the United States' nuclear weapons testing in the 1950’s (on islands nearly 200 miles downwind of the tests) were instrumental in the decision by the FDA in 1978 to issue a request for the availability of KI for thyroid protection in the event of a release from a commercial nuclear power plant or weapons-related nuclear incident. Noting that KI’s effectiveness was “virtually complete” and finding that iodine in the form of potassium iodide (KI) was substantially superior to other forms including iodate (KIO3) in terms of safety, effectiveness, lack of side effects, and speed of onset, the FDA invited manufacturers to submit applications to produce and market KI. [19] Today, three companies (Anbex, Inc., Fleming Co, and Recip of Sweden) have met the strict FDA requirements for manufacturing and testing of KI, and they offer products (IOSAT, ThyroShield, and Thyro-Safe, respectively) which are available for purchase.

Treatment for Erythema Nodosum

With erythema nodosum patients, potassium iodide can be used for persistent lesions whose cause remains unknown. It has been shown to be effective in cases of Crohn's disease.[20]

Adverse reactions

There have been some reports of potassium iodide treatment causing swelling of the parotid gland (one of the three glands which secrete saliva), due to its stimulatory effects on saliva production. [21]

A saturated solution of KI (SSKI) is typically given orally in adult doses of about 250 mg iodide several times a day (5 drops of SSKI assumed to be ⅓ mL) for thryoid blockage and occasionally as an expectorant. At these doses, and sometimes at much lower doses, side effects may include: acne, loss of appetite, or upset stomach (especially during the first several days, as the body adjusts to the medication). More severe side effects which require notification of a physician are: fever, weakness, unusual tiredness, swelling in the neck or throat, mouth sores, skin rash, nausea, vomiting, stomach pains, irregular heartbeat, numbness or tingling of the hands or feet, or a metallic taste in the mouth. [22]


Mild irritant, wear gloves. Chronic overexposure can have adverse effects on the thyroid. Potassium iodide is a possible teratogen


  1. ^ a b Phyllis A. Lyday "Iodine and Iodine Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim
  2. ^
  3. ^ Viscous liquids have about 15 drops per mL, not 20
  4. ^ N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, Pergamon Press, Oxford, UK, 1984
  5. ^ Handbook of Chemistry and Physics, 71st edition, CRC Press, Ann Arbor, Michigan, 1990
  6. ^ The Merck Index, 7th edition, Merck & Co., Rahway, New Jersey, 1960
  7. ^ L. G. Wade, Organic Chemistry, 5th ed., pp. 871-2, Prentice Hall, Upper Saddle RIver, New Jersey, 2003.
  8. ^ J. March, Advanced Organic Chemistry, 4th ed., pp. 670-1, Wiley, New York, 1992.
  9. ^ Xue, S.; Gu, R.; Wu, T.; Zhang, M.; Wang, X., Oral potassium iodide for the treatment of sporotrichosis, PMID 19821356 
  10. ^ [1] 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.
  11. ^ Guidelines for Iodine Prophylaxis following Nuclear Accidents, World Health Organization, Update 1999
  12. ^ US Nuclear Regulatory Commission, Report on the Accident at the Chernobyl Nuclear Power Station, NUREG-1250.
  13. ^ "Iodine Prophylaxis in Poland After the Chernobyl Reactor Accident: Benefits and Risks". American Journal of Medicine 94. 1993. 
  14. ^ US Food and Drug Administration, FDA Talk Paper: Guidance on Protection Against Thyroid Cancer in Case of a Nuclear Accident
  15. ^ US Nuclear Regulatory Commission, Assessment of the Use of Potassium Iodide (KI) As a Public Protective Action During Severe Reactor Accidents Quoting Thyroid Cancer in Children of Belarus Following the Chernobyl Accident, NUREG-1633
  16. ^ World Health Organization, Guidelines for Iodine Prophylaxis Following Nuclear Accidents, Update 1999. World Health Organization, Geneva
  17. ^ United Nations: Office for the Coordination of Humanitarian Affairs (OCHA), Chernobyl, a Continuing Catastrophe, New York and Geneva, 2000
  18. ^ "Thyroid Disease 60 Years After Hiroshima and 20 Years After Chernobyl". JAMA 295 (9). 2006. 
  19. ^ US Federal Register, Vol. 43, No. 242, Dec 15, 1978.
  20. ^ Marshall, JK; Irvine, EJ (September 1997). "Successful therapy of refractory erythema nodosum associated with Crohn's disease using potassium iodide.". Can J Gastroenterol 11 (6): 501–2. 
  21. ^ McCance; Huether. "Pathophysiology: The biological basis for disease in Adults and Children". 5th Edition. Elsievier Publishing
  22. ^

External links

Simple English

Potassium iodide

Potassium iodide is a chemical compound. Its chemical formula is KI. It has potassium and iodide ions in it.



It is a colorless crystalline solid. It is a weak reducing agent. It reacts with chlorine to make iodine and potassium chloride. It turns yellow when in air. This is because it reacts with oxygen and carbon dioxide to make iodine and potassium carbonate. It reacts with iodine to make the triiodide ion. That is why a solution of potassium iodide dissolves iodine.


It is made by reacting iodine or hydriodic acid with potassium hydroxide.


It is used to supply iodine in the form of vitamin tablets or pills. It can be added to table salt to prevent a deficiency of iodine. It is also used to make silver iodide. It can be used to add iodine to organic compounds]]. It is used to prevent thyroid cancer by filling up the thyroid with normal iodine. After a nuclear explosion there normally is radioactive iodine in the air. The radioactive iodine collects in the thyroid and causes cancer. When the person takes potassium iodide it fills up the thyroid with iodine so no radioactive iodine can come in.

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