Potassium Iodide
Potassium Iodide
OVERVIEW
Potassium iodide (poe-TAS-ee-yum EYE-oh-dide) is a white crystalline, granular, or powdered solid with a strong, bitter, salty taste. It is used as a feed additive, a dietary supplement, in photographic films, and in chemical research.
KEY FACTS
FORMULA:
KI
ELEMENTS:
Potassium, iodine
COMPOUND TYPE:
Binary salt (inorganic)
STATE:
Solid
MOLECULAR WEIGHT:
166.00 g/mol
MELTING POINT:
681°C (1260°F)
BOILING POINT:
1323°C (2413°F)
SOLUBILITY:
Soluble in water, ethyl alcohol, acetone, and glycerol
HOW IT IS MADE
A number of methods are available for the preparation of potassium iodide. In one procedure, elemental iodine (I2) is added to a solution of potassium hydroxide (KOH): I2 + 6KOH ? 5KI + KIO3 + 3H2O. The potassium iodide formed is separated from the potassium iodate (KIO3) by fractional crystallization. That is, the solution is warmed and then cooled. As the temperature falls, the two compounds, potassium iodide and potassium iodate, crystalize out at different temperatures and can be separated from each other. The potassium iodate can then be heated, causing it to decompose and make additional potassium iodide: 2KIO3 ? 2KI + 3O2.
Potassium iodide can also be produced by reacting hydriodic acid (HI) with potassium bicarbonate: HI + KHCO3 ? KI + CO2 + H2O.
Finally, the compound can be made by reacting iron (III) iodide with potassium carbonate (K2CO3): Fe3I8 + 4K2CO3 ? 8KI + 4CO2 + Fe3O4.
COMMON USES AND POTENTIAL HAZARDS
Potassium iodide is added to animal feeds to ensure that domestic animals get the iodine they need in their daily diets. A mixture of iodine in aqueous potassium iodide called SSKI has long been used as a disinfectant. The active agent in this mixture is iodine, and the potassium iodide is added to increase the iodine's solubility in water. SSKI is used to purify small amounts of water, to clear up pimples, to prevent sinus infections, and to treat bladder, lung, and stomach infections.
Perhaps the best known use of potassium iodide today is as a treatment for radiation exposure. When a nuclear bomb explodes or a nuclear accident occurs, one of the most dangerous products released to the environment is a radioactive isotope known as iodine-131. Iodine-131 enters the human body and travels to the thyroid, where it attacks cells and tissues, eventually resulting in thyroid cancer. Experts recommend that people exposed to radiation take potassium iodide as a protection against this hazard. The potassium iodide saturates the thyroid gland, making it difficult for the gland to absorb radioactive iodine that may enter the body.
Potassium iodide is also used in the production of photographic film and in a number of chemical tests, such as the determination of dissolved oxygen in water and the presence of starch in an unknown mixture.
Interesting Facts
- Iodized salt contains a small amount of potassium iodide. The potassium iodide is added to ensure that people get enough iodine in their daily diet. A deficiency of iodine results in a medical condition known as goiter, a large swelling in the neck. Before iodized salt was available, many people failed to get enough iodine in their diets and goiter was a very common health problem.
- Potassium iodide occurs naturally in seaweed.
Words to Know
- RADIOACTIVE ISOTOPE
- A form of an element that gives off some form of radiation and changes into another element.
Under most circumstances, there are no health hazards associated with potassium iodide. Taking an excess of the compound may have harmful effects on the thyroid gland, however. For that reason, people with an overactive thyroid should not take potassium iodide unless so directed by their doctors. Also, a person should not take potassium iodide as a preventative treatment against radiation. It provides no protection in advance of radiation exposure and, in excessive amounts, can create problems of its own for the thyroid.
FOR FURTHER INFORMATION
"Frequently Asked Questions on Potassium Iodide (KI)." U.S. Food and Drug Administration. http://www.fda.gov/cder/drugprepare/KI_Q&A.htm (accessed on November 1, 2005).
"Potassium Iodide." J. T. Baker. http://www.jtbaker.com/msds/englishhtml/p5906.htm (accessed on November 1, 2005).
"Potassium Iodide (Systemic)." Medline Plus. http://www.nlm.nih.gov/medlineplus/druginfo/uspdi/202472.html (accessed on November 1, 2005).
Wright, Jonathan V. "One Mineral Can Help a Myriad of Conditions from Atherosclerosis to 'COPD' to Zits." Tahoma Clinic. http://www.tahoma-clinic.com/iodide.shtml (accessed on November 1, 2005).
See AlsoSilver Iodide