2 k 2 co 3 + 2 i 2 inorganic chemistry since the iodide ion is a mild reducing agent, i− is easily oxidised to iodine (i2) by powerful oxidising agents such as chlorine: 2 ki ( aq ) + cl 2 ( aq ) ⟶ 2 kcl ( aq ) + i 2 ( aq ) + cl2_-> 2 kcl_+ i2_ 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, hydriodic acid (hi) is a stronger reducing agent. like other iodide salts, ki forms triiodide (i−3) when combined with elemental iodine. ki ( aq ) + i 2 ( s ) ⟶ ki 3 ( aq ) + i2_-> ki3_ unlike i2, i−3 salts can be highly water-soluble. through this reaction, iodine is used in redox titrations. aqueous ki3, "lugol's solution", is used as a disinfectant and as an etchant for gold surfaces. potassium iodide and silver nitrate are used to make silver(i) iodide, which is used for high speed photographic film and for cloud seeding: ki ( aq ) + 9 agno 3 ( aq ) ⟶ agi ( s ) + kno 3 ( aq ) + 9agno3_-> agi_+ kno3_ 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. ki, acting as a source of iodide, may also act as a nucleophilic catalyst for the alkylation of alkyl chlorides, bromides, or mesylates. history potassium iodide has been used medically since at least 1820. some of the earliest uses included cures for syphilis, lead and mercury poisoning. chernobyl potassium iodide's (ki) value as a radiation protective (thyroid blocking) agent was demonstrated 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 as a preventative measure against accumulation of radioactive 131i in the thyroid gland. reports differ concerning whether people in the areas immediately surrounding chernobyl itself were given the supplement. however 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." 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 provide safe and effective protection against thyroid cancer caused by irradiation." 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." but equally important to the question of ki is the fact that radioactivity releases are not "local" events. researchers at the world health organization accurately located and counted the residents with cancer from chernobyl and were startled to find that "the increase in incidence 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." 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." hiroshima and nagasaki the chernobyl findings were consistent with studies of the effects of previous radioactivity releases. in 1945, several hundreds of thousands of people working and residing in the japanese cities of hiroshima and nagasaki were exposed to high levels of radiation after atomic bombs were detonated over the two cities by the united states. survivors of the a-bombings, also known as hibakusha, have markedly high rates of thyroid disease; a 2006 study of 4091 hibakusha found nearly half the participants (1833; 44.8%) had an identifiable thyroid disease. an editorial in the journal of the american medical association regarding thyroid diseases in both hibakusha and those affected by the chernobyl disaster reports that " straight line adequately describes the relationship between radiation dose and thyroid cancer incidence" and states "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." nuclear weapons testing the development of thyroid cancer among residents in the north pacific from radioactive fallout following the united states' nuclear weapons testing in the 1950s (on islands nearly 200 miles downwind of the tests) were instrumental in the 1978 decision by the fda 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 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. fukushima it was reported on 16 march 2011, that potassium iodide tablets were given preventively to u.s. naval air crew members flying within 70 nautical miles of the fukushima daiichi nuclear power plant damaged in the earthquake (8.9/9.0 magnitude) and ensuing tsunami on 11 march 2011. the measures were seen as precautions, and the pentagon said no u.s. forces have shown signs of radiation poisoning. by 20 march, the us navy instructed personnel coming within 100 miles of the reactor to take the pills. the netherlands distribution areas for iodine pills in the netherlands (2017). in the netherlands, the central storage of iodine-pills is located in zoetermeer, near the hague. in 2017, the dutch government distributed pills to hundreds of thousands of residents who lived within a certain distance of nuclear power plants and met some other criteria. belgium by 2020, potassium iodide tablets are made available free of charge for all residents in all pharmacies throughout the country. formulations three companies (anbex, inc., fleming co, and recipharm of sweden) have met the strict fda requirements for manufacturing and testing of ki, and they offer products (iosat, thyroshield, and thyrosafe, respectively) which are available for purchase. in 2012, fleming co. sold all its product rights and manufacturing facility to other companies and no longer exists. thyroshield is currently not in production. the swedish manufacturing facility for thyrosafe, a half-strength potassium iodide tablet for thyroid protection from radiation, was mentioned on the secret us 2008 critical foreign dependencies initiative leaked by wikileaks in 2010. tablets of potassium iodide are supplied for emergency purposes related to blockade of radioiodine uptake, a common form of radiation poisoning due to environmental contamination by the short-lived fission product 131i. potassium iodide may also be administered pharmaceutically for thyroid storm. for reasons noted above, therapeutic drops of sski, or 130 mg tablets of ki as used for nuclear fission accidents, are not used as nutritional supplements, since an sski drop or nuclear-emergency tablet provides 300 to 700 times more iodine than the daily adult nutritional requirement. dedicated nutritional iodide tablets containing 0.15 mg (150 micrograms (μg)) of iodide, from ki or from various other sources (such as kelp extract) are marketed as supplements, but they are not to be confused with the much higher pharmaceutical dose preparations. potassium iodide can be conveniently prepared in a saturated solution, abbreviated sski. this method of delivering potassium iodide doesn't require a method to weigh out the potassium iodide, thus allowing it to be used in an emergency situation. ki crystals are simply added to water until no more ki will dissolve and instead sits at the bottom of the container. with pure water, the concentration of ki in the solution depends only on the temperature. potassium iodide is highly soluble in water thus sski is a concentrated source of ki. at 20 degrees celsius the solubility of ki is 140-148 grams per 100 grams of water. because the volumes of ki and water are approximately additive, the resulting sski solution will contain about 1.00 gram (1000 mg) ki per milliliter (ml) of solution. this is 100% weight/volume (note units of mass concentration) of ki (one gram ki per ml solution), which is possible because sski is significantly more dense than pure water—about 1.67 g/ml. because ki is about 76.4% iodide by weight, sski contains about 764 mg iodide per ml. this concentration of iodide allows the calculation of the iodide dose per drop, if one knows the number of drops per milliliter. for sski, a solution more viscous than water, there are assumed to be 15 drops per ml; the iodide dose is therefore approximately 51 mg per drop. it is conventionally rounded to 50 mg per drop. the term sski is also used, especially by pharmacists, to refer to a u.s.p. pre-prepared solution formula, made by adding ki to water to prepare a solution containing 1000 mg ki per ml solution (100% wt/volume ki solution), to closely approximate the concentration of sski made by saturation. this is essentially interchangeable with sski made by saturation, and also contains about 50 mg iodide per drop. 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. the dose typically begins with a loading dose, then 1⁄3 ml sski (5 drops or 250 mg iodine as iodide), 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. 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. potassium iodide has been used for symptomatic treatment of erythema nodosum patients for persistent lesions whose cause remains unknown. it has been used in cases of erythema nodosum associated with crohn's disease. due to its high potassium content, sski is extremely bitter, and if possible it is administered in a sugar cube or small ball of bread. it may also be mixed into much larger volumes of juices. neither sski or ki tablets form nutritional supplements, since the nutritional requirement for iodine is only 150 micrograms (0.15 mg) of iodide per day. thus, a drop of sski provides 50/0.15 = 333 times the daily iodine requirement, and a standard ki tablet provides twice this much.