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For fertilizer.
| Atomic Number: |
19 |
| Atomic Symbol: |
K |
| Atomic Weight: |
39.098 |
| Electron Configuration: |
[Ar]4s1 |
History
(English, potash - pot ashes; L.. kalium, Arab qali, alkali) Discovered in 1807 by
Davy, who obtained it from caustic potash (KOH); this was the first metal isolated by
electrolysis.
Sources
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 from them only with
great difficulty.
Certain minerals, however, such as sylvite, carnallite, langbeinite, and polyhalite are
found in ancientlake 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 3000 ft 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.
Production
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).
Uses
The greatest demand for potash has been in its use for fertilizers. Potassium is an
essential constituent for plant growth and is found in most soils.
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.
Properties
It is one of the most reactive and electropositive of metals. Except for iridium, 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
must be preserved in a mineral oil such as kerosene.
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.
Isotopes
Seventeen isotopes of potassium are known. Ordinary potassium is composed of three
isotopes, one of which is 40oK
(0.0118%), a radioactive isotope with a half-life of 1.28 x 109 years.
Handling
The radioactivity presents no appreciable hazard.
Cost
Metallic potassium is available commercially for about $40/lb in small quantities.
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