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Chemical Fact Sheet

Potassium

Chemical Abstract Number (CAS #) 7440-09-7
Synonyms Kalium; Potassium,- (Liquidalloy); Potassium,-Metal
Analytical Methods 200.7 - 200.8 - 6010 - 6020
Atomic Symbol K

Synopsis from the CRC Handbook of Chemistry and Physics 92nd Edition 2011-2013

Potassium — (English, potash — pot ashes; L. kalium, Arab. qali, alkali), K; at. wt. 39.0983(1); at. no. 19; m.p. 63.5 °C; b.p. 759 °C; sp. gr. 0.89; valence 1. Discovered in 1807 by Davy, who obtained it from caustic potash (KOH); this was the first metal isolated by electrolysis. The metal is the seventh most abundant and makes up about 2.4% by weight of the Earth’s crust. Most potassium minerals are insoluble and the metal is obtained The Elements 4-27 from them only with great difficulty. Certain minerals, however, such as sylvite, carnallite, langbeinite, and polyhalite are found in ancient lake and sea beds and form rather extensive deposits from which potassium and its salts can readily be obtained. Potash is mined in Germany, New Mexico, California, Utah, and elsewhere. Large deposits of potash, found at a depth of some 1000 m in Saskatchewan, promise to be important in coming years. Potassium is also found in the ocean, but is present only in relatively small amounts compared to sodium. The greatest demand for potash has been in its use for fertilizers. Potassium is an essential constituent for plant growth and it is found in most soils. Potassium is never found free in nature, but is obtained by electrolysis of the hydroxide, much in the same manner as prepared by Davy. Thermal methods also are commonly used to produce potassium (such as by reduction of potassium compounds with CaC2, C, Si, or Na). It is one of the most reactive and electropositive of metals. Except for lithium, it is the lightest known metal. It is soft, easily cut with a knife, and is silvery in appearance immediately after a fresh surface is exposed. It rapidly oxidizes in air and should be preserved in a mineral oil. As with other metals of the alkali group, it decomposes in water with the evolution of hydrogen. It catches fire spontaneously on water. Potassium and its salts impart a violet color to flames. Twenty-one isotopes, one of which is an isomer, of potassium are known. Ordinary potassium is composed of three isotopes, one of which is 40K (0.0117%), a radioactive isotope with a half-life of 1.26 × 109 years. The radioactivity presents no appreciable hazard. An alloy of sodium and potassium (NaK) is used as a heat-transfer medium. Many potassium salts are of utmost importance, including the hydroxide, nitrate, carbonate, chloride, chlorate, bromide, iodide, cyanide, sulfate, chromate, and dichromate. Metallic potassium is available commercially for about $1200/ kg (98% purity) or $75/g (99.95% purity).
Use In synthesis of inorg potassium compd; As heat transfer medium together with sodium; In org syntheses involving condnsation, dehalogenation, reduction, & polymerization reactions. Laboratory reagent; seeding of combustion gases in magnetohydrodynamic generators; component of fertilizers Use of the vaporized metal in turbines has been reported
Consumption Patterns Primary use for potassium metal is NaK-78 /a sodium-potassium alloy/ (78% potassium) (1982)
Apparent Color Soft, Silvery-white metal; Body-centered cubic structure
Boiling Point 765.5 deg C
Melting Point 63.2 deg C
Molecular Weight 39.098
Density 0.856 @ 20 deg C

Chemical and

Physical Properties

Atomic number 19; Valence 1; Alkali metal; becomes brittle @ low temp; Specific heat (0 deg C): 0.176 cal/g deg; thermal conductivity (cal/sec deg C cm): 0.23 (21 deg C); 0.956 (400 deg C); one of most active metals; E(0) (AQ) K/K+ 2.922 volts Potassium & its salts impart a violet color to flames Heat of soln: -2,106 btu/lb= -1,169 cal/g= -48,91x10+5 J/kg Decomp in alc & in hot water, in cold water to potassium hydroxide Inert in argon, helium, & nitrogen Reacts vigorously with oxygen; with water even @ -100 deg C; with acids; with halogens; molten metal reacts with sulfur, with hydrogen sulfide; reacts with hydrogen slowly @ 200 deg C, rapidly @ 350-400 deg C; reacts slowly with anhydroun hydrogen halides @ room temp; reduces silicates, sulfates, nitrates, carbonates, phosphates, oxides & hydroxides of heavy metals, often with separation of metal; reacts with org compd containing active groups; inert to saturated aliphatic & to aromatic hydrocarbons

Environmental Fate

Occurrence in earth's crust: 2.59% by wt. potassium is never found free in nature Potassium is present in the composition of the kernel of Black Walnut Potassium in seawater at a concentration of 3.8X10-5 ug/L Potassium is present in ferromanganese nodules in the Pacific ocean at 0.753 wt% and in the Atlantic ocean at 0.56 wt% Commercial sources of potassium are usually limited to the natural deposits of sulfite, areanite or carnaltite.


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