Potassium 23055 224085773 2008-07-07T06:32:59Z Plantsurfer 1750837 Reverted [[WP:AGF|good faith]] edits by [[Special:Contributions/24.211.145.162|24.211.145.162]]; The change breaks the link. ([[WP:TW|TW]]) {{Infobox potassium}} '''Potassium''' ({{pronEng|pəˈtæsiəm}}) is a [[chemical element]]. It has the symbol '''K''' ({{lang-la|kalium}}) and [[atomic number]] 19. The name "potassium" comes from the word "potash", as potassium was first isolated from [[potash]]. Potassium is a soft silvery-white metallic [[alkali metal]] that occurs naturally bound to other elements in [[seawater]] and many [[mineral]]s. It [[redox|oxidizes]] rapidly in [[Earth's atmosphere|air]] and is very reactive with [[water]], generating sufficient heat to ignite the evolved hydrogen. In many respects, potassium and [[sodium]] are [[chemical]]ly similar, although they have very different functions in organisms in general, and in animal cells in particular. == Occurrence == {{seealso|Category:Potassium minerals}} [[Image:PotassiumFeldsparUSGOV.jpg|thumb|left|Potassium in [[feldspar]]]] Potassium metal is never found free, as it reacts violently with the abundant water in nature.<ref name = webelements/> As various compounds, potassium makes up about 1.5% of the weight of the [[Earth's crust]] and is the seventh most abundant element.<ref name = webelements>{{cite web | publisher = Webelements | title = Potassium: Key Information | url = http://www.webelements.com/webelements/elements/text/K/key.html | author = Mark Winter}}</ref> As it is very [[electropositive]], potassium metal is difficult to obtain from its minerals. Potassium salts such as [[carnallite]], [[langbeinite]], [[polyhalite]], and [[sylvite]] form extensive deposits in ancient lake and [[seabed]]s, making extraction of potassium salts in these environments commercially viable. The principal source of potassium, [[potash]], is mined in [[Saskatchewan]], [[California]], [[Germany]], [[New Mexico]], [[Utah]], and in other places around the world. Three thousand feet below the surface of [[Saskatchewan]] are large deposits of potash which are important sources of this element and its salts, with several large mines in operation since the 1960s. Saskatchewan pioneered the use of freezing of wet sands (the Blairmore formation) in order to drive mine shafts through them. The main mining company is the [[Potash Corporation of Saskatchewan]]. The [[ocean]]s are another source of potassium, but the quantity present in a given volume of seawater is relatively low compared with sodium. ==Production== Pure potassium metal can be isolated by [[electrolysis]] of its [[potassium hydroxide|hydroxide]] in a process that has changed little since [[Humphry Davy|Davy]].<ref name = webelements/> Thermal methods also are employed in potassium production, using [[potassium chloride]].{{Fact|date=February 2008}} == Isotopes ==<!-- This section is linked from [[Uranium]] --> {{main|isotopes of potassium}} There are 24 known [[isotope]]s of potassium. Three isotopes occur naturally: <sup>39</sup>K (93.3%), <sup>40</sup>K (0.0117%) and <sup>41</sup>K (6.7%). Naturally occurring <sup>40</sup>K decays to stable [[Argon|<sup>40</sup>Ar]] (11.2%) by [[electron capture]] and by [[positron emission]], and decays to stable [[Calcium|<sup>40</sup>Ca]] (88.8%) by [[beta decay]]; <sup>40</sup>K has a [[half-life]] of 1.250&times;10<sup>9</sup> years. The decay of <sup>40</sup>K to <sup>40</sup>Ar enables a commonly used method for dating rocks. The conventional [[Potassium-argon dating|K-Ar dating method]] depends on the assumption that the rocks contained no argon at the time of formation and that all the subsequent radiogenic argon (i.e., <sup>40</sup>Ar) was quantitatively retained. [[Mineral]]s are dated by measurement of the concentration of potassium and the amount of radiogenic <sup>40</sup>Ar that has accumulated. The minerals that are best suited for dating include [[biotite]], [[muscovite]], plutonic/high grade metamorphic [[hornblende]], and volcanic [[feldspar]]; whole rock samples from volcanic flows and shallow instrusives can also be dated if they are unaltered. Outside of dating, potassium isotopes have been used extensively as [[radioactive tracer|tracer]]s in studies of [[weathering]]. They have also been used for [[nutrient cycling]] studies because potassium is a [[macronutrient (ecology)|macronutrient]] required for [[life]]. <sup>40</sup>K occurs in natural potassium (and thus in some commercial salt substitutes) in sufficient quantity that large bags of those substitutes can be used as a radioactive source for classroom demonstrations. In healthy animals and people, <sup>40</sup>K represents the largest source of radioactivity, greater even than <sup>14</sup>C. In a human body of 70 kg mass, about 4,400 nuclei of <sup>40</sup>K decay per second.<ref>{{cite web |url=http://www.fas.harvard.edu/~scdiroff/lds/QuantumRelativity/RadioactiveHumanBody/RadioactiveHumanBody.html |title=background radiation - potassium-40 - γ radiation}}</ref> The activity of natural potassium is 31 [[Becquerel|Bq]]/g. ==Properties== {{Unreferencedsection|date=February 2008}} ===Physical properties=== [[Image:FlammenfärbungK.png|thumb|100px|The flame test]] Potassium is the second least dense metal; only [[lithium]] is less dense. It is a soft, low-melting solid that can easily be cut with a knife. Freshly cut potassium is silvery in appearance, but in air it begins to tarnish toward grey immediately.<ref name = webelements/> In a [[flame test]], potassium and its compounds emit a pale violet color, which may be masked by the strong yellow emission of sodium if it is also present. [[Cobalt glass]] can be used to filter out the yellow sodium color.<ref>{{cite web | publisher = [[About.com]] | title = Qualitative Analysis - Flame Tests | author = Anne Marie Helmenstine | url = http://chemistry.about.com/library/weekly/aa110401a.htm}}</ref> Potassium concentration in solution is commonly determined by [[photoelectric flame photometer|flame photometry]], [[atomic absorption spectrophotometry]], [[inductively coupled plasma]], or [[ion selective electrode]]s. ===Chemical properties=== Potassium must be protected from air for storage to prevent disintegration of the metal from oxide and hydroxide corrosion. Often samples are maintained under a [[Redox|reducing]] medium such as [[kerosene]]. Like the other alkali metals, potassium reacts violently with water, producing [[hydrogen]]. The reaction is notably more violent than that of lithium or sodium with water, and is sufficiently exothermic that the evolved hydrogen gas ignites. :2K(s) + 2H<sub>2</sub>O(l) → H<sub>2</sub>(g) + 2KOH(aq) Because potassium reacts quickly with even traces of water, and its reaction products are nonvolatile, it is sometimes used alone, or as [[NaK]] (an alloy with [[sodium]] which is liquid at room temperature) to dry [[solvent]]s prior to distillation. In this role, it serves as a potent [[desiccant]]. Potassium hydroxide reacts strongly with carbon dioxide to produce potassium carbonate, and is used to remove traces of CO<sub>2</sub> from air. Potassium compounds generally have excellent water solubility, due to the high hydration energy of the K<sup>+</sup> ion. The potassium ion is colorless in water. Methods of separating potassium by [[Precipitation (chemistry)|precipitation]], sometimes used for [[gravimetric analysis]], include the use of sodium tetraphenyl boron, [[hexachloroplatinic acid]], and [[sodium cobaltinitrite]]. ==Potassium cations in the body== ===Biochemical function=== {{Main|Action potential}} Potassium [[ion|cations]] are important in [[neuron]] ([[brain]] and [[nerve]]) function, and in influencing [[osmoregulation|osmotic balance]] between cells and the [[extracellular fluid|interstitial fluid]].<ref>{{cite book |last = Campbell |first = Neil |title = Biology |date=1987 |isbn = 0-8053-1840-2 |pages = 795 }}</ref>. Potassium may be detected by taste because it triggers three of the five types of tastebuds, according to concentration. Dilute solutions of potassium ion taste sweet (allowing moderate concentrations in milk and juices), while higher concentrations become increasingly bitter/alkaline, and finally also salty to the taste. The combined bitterness and saltiness of high potassium content solutions makes high-dose potassium supplementation by liquid drinks a palatability challenge.{{Fact|date=December 2007}} ===Membrane polarization=== {{Unreferencedsection|date=February 2008}} Potassium is also important in allowing [[muscle contraction]] and the sending of all nerve impulses in animals through [[action potential]]s. By nature of their electrostatic and chemical properties, K<sup>+</sup> ions are larger than Na<sup>+</sup> ions, and ion channels and pumps in cell membranes can distinguish between the two types of ions, actively pumping or passively allowing one of the two ions to pass, while blocking the other. <ref>{{cite web|url=http://www.ncbi.nlm.nih.gov/pubmed/17472437|title=Structural and thermodynamic properties of selective ion binding in a K+ channel|author=Lockless SW, Zhou M, MacKinnon R.|publisher=Laboratory of Molecular Neurobiology and Biophysic, Rockefeller University|accessdate=2008-03-08}}</ref> A shortage of potassium in body fluids may cause a potentially fatal condition known as [[hypokalemia]], typically resulting from [[diarrhea]], increased [[diuresis]] and vomiting. Deficiency symptoms include muscle weakness, paralytic ileus, ECG abnormalities, decreased reflex response and in severe cases respiratory paralysis, [[alkalosis]] and [[cardiac arrhythmia]]. ===Filtration and excretion=== Potassium is an essential mineral [[micronutrient (ecology)|micronutrient]] in human nutrition; it is the major cation (positive ion) inside animal cells, and it is thus important in maintaining fluid and [[electrolyte]] balance in the body. [[Sodium]] makes up most of the [[cations]] of blood plasma at about 145 [[milliequivalents]] per liter (3345 milligrams) and potassium makes up most of the cell fluid cations at about 150 milliequivalents per liter (4800 milligrams). Plasma is filtered through the [[glomerulus]] of the kidneys in enormous amounts, about 180 liters per day.<ref name=Potts1964>{{cite book | author = Potts, W.T.W. | coauthors = Parry, G. | year = 1964 | title = Osmotic and ionic regulation in animals | publisher = [[Pergamon Press]] | isbn = }}</ref> Thus 602,000 milligrams of sodium and 33,000 milligrams of potassium are filtered each day. All but the 1000-10,000 milligrams of sodium and the 1000-4000 milligrams of potassium likely to be in the diet must be reabsorbed. Sodium must be reabsorbed in such a way as to keep the blood volume exactly right and the osmotic pressure correct; potassium must be reabsorbed in such a way as to keep serum concentration as close as possible to 4.8 milliequivalents (about 190 milligrams) per liter.<ref>{{cite journal |author=Lans HS, Stein IF, Meyer KA |title=The relation of serum potassium to erythrocyte potassium in normal subjects and patients with potassium deficiency |journal=Am. J. Med. Sci. |volume=223 |issue=1 |pages=65–74 |year=1952 |pmid=14902792| doi = 10.1097/00000441-195201000-00011 <!--Retrieved from CrossRef by DOI bot-->}}</ref> Sodium pumps must always operate to conserve sodium. Potassium must sometimes be conserved also, but since the amount of potassium in the blood plasma is very small and the pool of potassium in the cells is about thirty times as large, the situation is not so critical for potassium. Since potassium is moved passively<ref>{{cite journal |author=Bennett CM, Brenner BM, Berliner RW |title=Micropuncture study of nephron function in the rhesus monkey |journal=J Clin Invest |volume=47 |issue=1 |pages=203–216 |year=1968 |pmid=16695942 |doi=}}</ref><ref> {{cite journal |author=Solomon AK |title=Pumps in the living cell |journal=Sci. Am. |volume=207 |issue= |pages=100–8 |year=1962 |pmid=13914986 |doi=}}</ref> in counter flow to sodium in response to an apparent (but not actual) [[Donnan equilibrium]],<ref>{{cite book |author=Kernan, Roderick P. |title=Cell potassium (Transport in the life sciences) |publisher=[[John Wiley & Sons|Wiley]] |location=New York |year=1980 |pages= |isbn= 0471048062 |oclc= |doi=}}; p. 40 & 48.</ref> the urine can never sink below the concentration of potassium in serum except sometimes by actively excreting water at the end of the processing. Potassium is secreted twice and reabsorbed three times before the urine reaches the collecting tubules.<ref>{{cite journal |author=Wright FS |title=Sites and mechanisms of potassium transport along the renal tubule |journal=Kidney Int. |volume=11 |issue=6 |pages=415–32 |year=1977 |pmid=875263| doi = 10.1038/ki.1977.60 <!--Retrieved from CrossRef by DOI bot-->}}</ref> At that point, it usually has about the same potassium concentration as plasma. If potassium were removed from the diet, there would remain a minimum obligatory kidney excretion of about 200 mg per day when the serum declines to 3.0-3.5 milliequivalents per liter in about one week,<ref>{{cite journal |author=Squires RD, Huth EJ |title=Experimental potassium depletion in normal human subjects. I. Relation of ionic intakes to the renal conservation of potassium |journal=J. Clin. Invest. |volume=38 |issue=7 |pages=1134–48 |year=1959 |pmid=13664789| doi = 10.1172/JCI103890 <!--Retrieved from CrossRef by DOI bot-->}}</ref> and can never be cut off completely. Because it cannot be cut off completely, death will result when the whole body potassium declines to the vicinity of one-half full capacity. At the end of the processing, potassium is secreted one more time if the serum levels are too high. The potassium moves passively through pores in the cell wall. When ions move through pumps there is a gate in the pumps on either side of the cell wall and only one gate can be open at once. As a result 100 ions are forced through per second. Pores have only one gate and there one kind of ion only can stream through at 10 million to 100 million ions per second.<ref>{{cite journal |author=Gadsby DC |title=Ion transport: spot the difference |journal=Nature |volume=427 |issue=6977 |pages=795–7 |year=2004 |pmid=14985745 |doi=10.1038/427795a}}; for a diagram of the potassium pores are viewed, see {{cite journal |author=Miller C |title=See potassium run |journal=Nature |volume=414 |issue=6859 |pages=23–4 |year=2001 |pmid=11689922 |doi=10.1038/35102126}}</ref> The pores require calcium in order to open<ref>{{cite journal |author=Jiang Y, Lee A, Chen J, Cadene M, Chait BT, MacKinnon R |title=Crystal structure and mechanism of a calcium-gated potassium channel |journal=Nature |volume=417 |issue=6888 |pages=515–22 |year=2002 |pmid=12037559 |doi=10.1038/417515a}}</ref> although it is thought that the calcium works in reverse by blocking at least one of the pores.<ref>{{cite journal |author=Shi N, Ye S, Alam A, Chen L, Jiang Y |title=Atomic structure of a Na+- and K+-conducting channel |journal=Nature |volume=440 |issue=7083 |pages=570–4 |year=2006 |pmid=16467789 |doi=10.1038/nature04508}}; includes a detailed picture of atoms in the pump.</ref> Carbonyl groups inside the pore on the amino acids mimics the water hydration that takes place in water solution<ref>{{cite journal |author=Zhou Y, Morais-Cabral JH, Kaufman A, MacKinnon R |title=Chemistry of ion coordination and hydration revealed by a K+ channel-Fab complex at 2.0 A resolution |journal=Nature |volume=414 |issue=6859 |pages=43–8 |year=2001 |pmid=11689936 |doi=10.1038/35102009}}</ref> by the nature of the electrostatic charges on four carbonyl groups inside the pore.<ref>{{cite journal |author=Noskov SY, Bernèche S, Roux B |title=Control of ion selectivity in potassium channels by electrostatic and dynamic properties of carbonyl ligands |journal=Nature |volume=431 |issue=7010 |pages=830–4 |year=2004 |pmid=15483608 |doi=10.1038/nature02943}}</ref> ===Potassium in the diet=== Adequate intake can generally be guaranteed by eating a variety of foods containing potassium and deficiency is rare in healthy individuals eating a balanced diet. Foods with high sources of potassium include [[orange juice]], [[potato]]es, [[banana]]s, [[avocado]]s, [[tomato]]es, [[broccoli]], [[soybeans]] and [[apricot]]s, although it is also common in most [[fruit]]s, [[vegetable]]s and [[meat]]s <ref>http://www.pamf.org/patients/pdf/potassium_count.pdf</ref>. Diets high in potassium can reduce the risk of [[hypertension]] and a potassium deficiency combined with an inadequate [[thiamine]] intake has produced heart disease in rats.<ref name=Folis1942>{{cite journal | author = Folis, R.H. | year = 1942 | title = Myocardial Necrosis in Rats on a Potassium Low Diet Prevented by Thiamine Deficiency | journal = Bull. Johns-Hopkins Hospital | volume = 71 | pages = 235}}</ref> The [[2004]] guidelines of the [[Institute of Medicine]] specify a [[Dietary reference intake|DRI]] of 4,000mg of potassium, though most Americans consume only half that amount per day.<ref>{{cite journal |author=Grim CE, Luft FC, Miller JZ, ''et al'' |title=Racial differences in blood pressure in Evans County, Georgia: relationship to sodium and potassium intake and plasma renin activity |journal=J Chronic Dis |volume=33 |issue=2 |pages=87–94 |year=1980 |pmid=6986391| doi = 10.1016/0021-9681(80)90032-6 <!--Retrieved from CrossRef by DOI bot-->}}</ref> Similarly, in the [[European Union]], particularly in [[Germany]] and [[Italy]], insufficient potassium intake is somewhat common.<ref>{{cite journal | url = http://content.karger.com/ProdukteDB/produkte.asp?Aktion=ShowPDF&ProduktNr=223977&Ausgabe=230671&ArtikelNr=83312&filename=83312.pdf | format = pdf | last = Karger | first = S. | journal = Ann Nutr Metab | year = 2004 | volume = 48 | issue = 2 (suppl) | pages = 1–16 | title = Energy and nutrient intake in the European Union}}</ref> Supplements of potassium in medicine are most widely used in conjunction with [[loop diuretic]]s and [[thiazide]]s, classes of diuretics which rid the body of sodium and water, but have the side effect of also causing potassium loss in urine. A variety of medical supplements are available. If potassium supplements are used, such as sodium free baking powder and sodium free table salt, inadequate [[thiamine]] can cause [[beriberi]].<ref>{{cite journal | last = Mineno | first = T | year = 1969 | title = Effect of some vitamins and other substances on K metabolism in the myocardia of vitamin deficient rats - Experimental investigation. | journal = J. Nagoya Med. Assoc. | volume = 92; | pages = 80–95}}</ref><ref>{{cite book | last = Gould | first = SE (ed) | year = 1968 | title = Pathology of the Heart and Blood Vessels | publisher = Charles C. Thomas | pages = 851}} p. 508.</ref> <!--neither cite shows or even suggests human beri beri as a result of potassium supplements--> {{Fact|date=January 2008}} Individuals suffering from [[kidney]] diseases may suffer adverse health effects from consuming large quantities of dietary potassium. [[Chronic kidney disease|End stage renal failure]] patients undergoing therapy by [[renal dialysis]] must observe strict dietary limits on potassium intake, since the kidneys control potassium excretion, and buildup of blood concentrations of potassium may trigger fatal cardiac arrhythmia. Acute [[hyperkalemia]] can be reduced through eating baking soda,<ref>{{cite journal |author=Berliner RW, Kennedy TJ, Orloff J |title=Relationship between acidification of the urine and potassium metabolism; effect of carbonic anhydrase inhibition on potassium excretion |journal=Am. J. Med. |volume=11 |issue=3 |pages=274–82 |year=1951 |pmid=14877833| doi = 10.1016/0002-9343(51)90165-9 <!--Retrieved from CrossRef by DOI bot-->}}</ref> or [[glucose]],<ref>{{cite journal |author=Knochel JP |title=Diuretic-induced hypokalemia |journal=Am. J. Med. |volume=77 |issue=5A |pages=18–27 |year=1984 |pmid=6496556| doi = 10.1016/S0002-9343(84)80004-2 <!--Retrieved from CrossRef by DOI bot-->}}</ref><ref>{{cite journal |author=Kolb H, Burkart V |title=Nicotinamide in type 1 diabetes. Mechanism of action revisited |journal=Diabetes Care |volume=22 Suppl 2 |issue= |pages=B16–20 |year=1999 |pmid=10097894 |doi=}}</ref> [[hyperventilation]]<ref>{{cite journal |author=Kilburn KH |title=Movements of potassium during acute respiratory acidosis and recovery |journal=J Appl Physiol |volume=21 |issue=2 |pages=679–84 |year=1966 |pmid=5934480 |doi=}}</ref> and [[perspiration]].<ref>{{cite journal |author=Consolazio CF, Matoush LO, Nelson RA, Harding RS, Canham JE |title=Excretion of sodium, potassium, magnesium and iron in human sweat and the relation of each to balance and requirements |journal=J. Nutr. |volume=79 |issue= |pages=407–15 |year=1963 |pmid=14022653 |doi=}}</ref> == Applications == ===Biological applications=== Potassium is an essential component of [[plant]] nutrition and is found in most [[soil]] types. Its primary use in [[agriculture]], [[horticulture]] and [[hydroponic]] culture as a [[fertilizer]] as the [[Potassium chloride|chloride]] (KCl), [[Potassium sulfate|sulfate]] ({{chem|K|2|SO|4}}) or [[Potassium nitrate|nitrate]] ({{chem|KNO|3}}). In [[animal]] [[cell (biology)|cell]]s, potassium ions are vital to keeping cells alive (see [[Na-K pump]]). ===Food applications=== Potassium is a nutrient necessary for human life and health. [[Potassium chloride]] is used as a substitute for [[table salt]] by those seeking to reduce sodium intake so as to control [[hypertension]]. Good dietary sources of potassium include celery juice.<ref>Celery - Nutritional Analysis http://www.juicingbook.com/vegetables/celery</ref> The [[USDA]] lists tomato paste, orange juice, beet greens, white beans, bananas, and many other good dietary sources of potassium, ranked according to potassium content per measure shown.<ref>)Potassium / K (mg.) Content of Selected Foods per Common Measure, sorted by nutrient content | USDA National Nutrient Database for Standard Reference, Release 20 http://www.nal.usda.gov/fnic/foodcomp/Data/SR20/nutrlist/sr20w306.pdf</ref> Potassium sodium tartrate, or [[Rochelle salt]] ({{chem|KNaC|4|H|4|O|6}}) is the main constituent of [[baking powder]]. [[Potassium bromate]] ({{chem|KBrO|3}}) is a strong oxidiser, used as a flour improver (E924) to improve dough strength and rise height. The [[sulfite]] compound, [[Potassium bisulfite]] ({{chem|KHSO|3}}) is used as a food preservative, for example in [[wine]] and [[beer]]-making (but not in meats). It is also used to [[bleach]] textiles and straw, and in the tanning of [[leather]]s. Non-dietary uses of [[potassium chloride]] include its use to stop the heart, e.g. in [[cardiac surgery]] and in a solution used in executions by [[lethal injection]]. ===Industrial applications=== Potassium vapor is used in several types of [[magnetometer]]s. An [[alloy]] of sodium and potassium, [[NaK]] (usually pronounced "nack"), that is liquid at room temperature, is used as a heat-transfer medium. It can also be used as a [[desiccant]] for producing [[air-free technique|dry and air-free solvents]]. Potassium metal reacts vigorously with all of the halogens to form the corresponding potassium halides, which are white, water-soluble salts with [[cubic crystal system|cubic crystal morphology]]. [[Potassium bromide]] (KBr), [[potassium iodide]] (KI) and [[potassium chloride]] (KCl) are used in [[photographic emulsion]] to make the corresponding [[photosensitive]] [[silver halide]]s. [[Potassium hydroxide]] {{chem|KOH}} is a strong base, used in industry to neutralize strong and weak [[acid]]s and thereby finding uses in [[pH]] control and in the manufacture of potassium [[salt (chemistry)|salts]]. Potassium hydroxide is also used to [[saponification|saponify]] [[fat]]s and [[oils]] and in [[hydrolysis]] reactions, for example of [[esters]] and in industrial cleaners. [[Potassium nitrate]] {{chem|KNO|3}} or saltpeter is obtained from natural sources such as [[guano]] and [[evaporites]] or manufactured by the [[Haber process]] and is the [[oxidant]] in [[gunpowder]] ([[black powder]]) and an important agricultural fertilizer. [[Potassium cyanide]] {{chem|KCN}} is used industrially to dissolve [[copper]] and precious metals particularly [[silver]] and [[gold]] by forming [[complex (chemistry)|complex]]es; applications include [[gold mining]], [[electroplating]] and [[electroforming]] of these [[metal]]s. It is also used in [[organic synthesis]] to make [[nitriles]]. [[Potassium carbonate]] {{chem|K|2|CO|3}}, also known as potash, is used in the manufacture of glass and soap and as a mild desiccant. [[Potassium chromate]] (K<sub>2</sub>CrO<sub>4</sub>) is used in [[dye]]s and [[stain]]s (bright yellowish-red colour), in [[explosive]]s and [[fireworks]], in [[safety match]]es, in the tanning of leather and in [[fly paper]]. Potassium fluorosilicate (K<sub>2</sub>SiF<sub>6</sub>) is used in specialized glasses, [[ceramic]]s, and [[Vitreous enamel|enamel]]s. Potassium sodium tartrate, or [[Rochelle salt]] (KNaC<sub>4</sub>H<sub>4</sub>O<sub>6</sub>) is used in the [[silvering]] of [[mirror]]s. The [[superoxide]] KO<sub>2</sub> is an orange coloured solid used as a portable source of oxygen and as a carbon dioxide absorber. It is useful in [[Rebreather#Rebreathers whose absorbent releases oxygen|portable respiration systems]]. It is widely used in submarines and spacecrafts as it takes extreamely less volume than O<sub>2</sub>(g). 4KO<sub>2</sub> + 2CO<sub>2</sub> --- 2K<sub>2</sub>CO<sub>3</sub> + O<sub>2</sub> 4KO<sub>2</sub> + 4CO<sub>2</sub> --- 4KHCO<sub>3</sub> + 3O<sub>2</sub> [[Potassium chlorate]] {{chem|KClO|3}} is a strong oxidant, used in [[percussion caps]] and [[safety matches]] and in agriculture as a [[weedkiller]]. [[Glass]] may be treated with molten [[potassium nitrate]] {{chem|KNO|3}} to make [[toughened glass]], which is much stronger than regular glass. == History == {{Unreferencedsection|date=February 2008}} {{Expand-section|date=June 2008}} Potassium was discovered in 1807 by Sir [[Humphry Davy]], who derived it from [[caustic potash]] (K[[hydroxide|OH]]). Before the 18th century, no distinction was made between potassium and sodium. Potassium was the first metal that was isolated by electrolysis.<ref name=Enghag2004>{{cite book | author = Enghag, P. | year = 2004 | title = Encyclopedia of the elements | publisher = Wiley-VCH Weinheim | isbn = }}</ref> Potassium was not known in [[Ancient Rome|Roman]] times, and its names are not [[Classical Latin]] but rather [[neo-Latin]]. *The name '''kalium''' was taken from the word "[[alkali]]", which came from [[Arabic language|Arabic]] ''al qalīy'' = "the calcined ashes". *The name '''potassium''' was made from the word "potash", which is English, and originally meant an [[alkali]] extracted in a ''pot'' from the ''ash'' of burnt wood or tree leaves. == Precautions == {{Expand-section|additional citations|date=February 2008}} [[Image:KPeroxides.jpg|left|thumb|Peroxides (Yellow) and Ozonides (Red) on surface of potassium metal.]] Potassium reacts very violently with water producing [[hydrogen]] gas which then usually catches fire. Potassium is usually kept under a mineral oil such as kerosene to stop the metal reacting with water vapour present in the air. Unlike lithium and sodium, however, potassium should not be stored under oil indefinitely. If stored longer than 6 months to a year, dangerous shock-sensitive [[peroxide]]s can form on the metal and under the lid of the container, which can detonate upon opening. It is recommended that potassium, [[rubidium]] or [[caesium]] not be stored for longer than three months unless stored in an inert (oxygen free) atmosphere, or under vacuum.<ref>{{cite web |url=http://www.ncsu.edu/ehs/www99/right/handsMan/lab/Peroxide.pdf |title=DANGER: PEROXIDIZABLE CHEMICALS |author=Thomas K. Wray |publisher=Environmental Health &amp; Public Safety ([[North Carolina State University]])}}</ref> As potassium reacts with water to produce highly flammable [[hydrogen]] gas, a potassium fire is only exacerbated by the addition of water, and only a few dry chemicals are effective for putting out such a fire (see the precaution section in [[sodium]]). Potassium also produces [[potassium hydroxide]] (KOH) in the reaction with water. [[Potassium hydroxide]] which is an strong [[alkali]] and so is a caustic hazard causing burns. Due to the highly reactive nature of potassium, it should be handled with great care, with full skin and eye protection being used and preferably a explosive resistant barrier between the user and the source of the potassium. == References == {{reflist}} == See also == * [[:Category:Potassium compounds|Potassium compounds]] * [[Potassium in biology]] == External links == {{Commons|Potassium}} {{wiktionary|potassium}} *[http://www.webelements.com/webelements/elements/text/K/index.html WebElements.com &ndash; Potassium] {{alkalimetals}} {{Compact periodic table}} [[Category:Alkali metals]] [[Category:Chemical elements]] [[Category:Desiccants]] [[Category:Dietary minerals]] [[Category:Potassium|*]] [[af:Kalium]] [[ar:بوتاسيوم]] [[ast:Potasiu]] [[bn:পটাশিয়াম]] [[zh-min-nan:K (goân-sò͘)]] [[be:Калій]] [[bs:Kalijum]] [[bg:Калий]] [[ca:Potassi]] [[cs:Draslík]] [[co:Potassiu]] [[cy:Potasiwm]] [[da:Kalium]] [[de:Kalium]] [[dv:ޕޮޓޭސިއަމް]] [[et:Kaalium]] [[el:Κάλιο]] [[es:Potasio]] [[eo:Kalio]] [[eu:Potasio]] [[fa:پتاسیم]] [[fr:Potassium]] [[fur:Potassi]] [[ga:Potaisiam]] [[gv:Potashum]] [[gl:Potasio]] [[ko:칼륨]] [[hy:Կալիում]] [[hi:पोटासियम]] [[hr:Kalij]] [[io:Kalio]] [[id:Kalium]] [[is:Kalín]] [[it:Potassio]] [[he:אשלגן]] [[jv:Kalium]] [[kn:ಪೊಟ್ಯಾಶಿಯಮ್]] [[sw:Kali]] [[ht:Potasyòm]] [[ku:Qelye]] [[la:Kalium]] [[lv:Kālijs]] [[lb:Kalium]] [[lt:Kalis]] [[jbo:sodnrkali]] [[hu:Kálium]] [[mk:Калиум]] [[ml:പൊട്ടാസ്യം]] [[mi:Konurehu]] [[ms:Kalium]] [[nl:Kalium]] [[ja:カリウム]] [[no:Kalium]] [[nn:Kalium]] [[nov:Kalium]] [[oc:Potassi]] [[uz:Kaliy]] [[nds:Kalium]] [[pl:Potas]] [[pt:Potássio]] [[ro:Potasiu]] [[qu:Kalyu]] [[ru:Калий]] [[sq:Kaliumi]] [[scn:Putassiu]] [[simple:Potassium]] [[sk:Draslík]] [[sl:Kalij]] [[sr:Калијум]] [[sh:Kalij]] [[fi:Kalium]] [[sv:Kalium]] [[th:โพแทสเซียม]] [[vi:Kali]] [[tg:Калий]] [[tr:Potasyum]] [[uk:Калій]] [[ur:پوٹاشیم]] [[wa:Potassiom]] [[vls:Kalium]] [[zh-yue:鉀]] [[zh:钾]]