'Potassium' (
IPA: ) is a
chemical element. It has the symbol 'K' ( → ) 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
minerals. It
oxidizes rapidly in
air and is very reactive, especially towards
water. In many respects, potassium and
sodium are
chemically similar, although organisms in general, and animal cells in particular, treat them very differently.
Notable characteristics
Physical
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 gray visibly and immediately. 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
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
2O(l) → H
2(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
solvents prior to distillation. In this role, it serves as a potent
desiccant.
Potassium and its compounds emit a
violet color in a flame. This fact is the basis of the
flame test for the presence of potassium in a sample.
Potassium compounds generally have excellent water solubility, due to the high hydration energy of the K
+ ion. The potassium ion is colorless in water.
Potassium concentration in solution is commonly determined by
flame photometry,
atomic absorption spectrophotometry,
inductively coupled plasma, or
ion selective electrodes. Methods of separating potassium by
precipitation, sometimes used for
gravimetric analysis, include the use of
sodium tetraphenyl boron,
dihydrogen hexachloroplatinate (IV) hexahydrate, and
sodium cobaltinitrite.
Biochemicial
Potassium is important in
nerve function and in influencing
osmotic balance between cells and the
interstitiual fluid.
[1]
Potassium may be detected by taste because it triggers all the 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.
Applications
Agriculture and health
★ It is primarily used in
fertilizers as either the
chloride,
sulfate or
carbonate - not as the
oxide.
★ Potassium is an essential component needed in
plant growth and is found in most
soil types.
★ In
animal cells potassium ions are vital to keeping cells alive (see
Na-K pump)
★
Potassium chloride is used as a substitute for
table salt and is also used to stop the heart, e.g. in
cardiac surgery and in executions by
lethal injection in a solution.
★
Potassium bisulfite (KHSO
3) is used as a food preservative (but not in meats),
bleaching of
textiles and
straw,
wine and
beer-making and in the tanning of
leathers.
★
Potassium bromate (KBrO
3) is used as a flour improver (E924).
★ Potassium sodium tartrate, or
Rochelle salt (KNaC
4H
4O
6) is used in
baking powder and
medicine.
★
Potassium pyrophosphate (K
4P
2O
7) is used in
soaps and
detergents.
★ Potassium fluorosilicate (K
2SiF
6) is used as an
insecticide.
Industrial
★
Potassium hydroxide is an important industrial chemical used as a strong base.
★
Potassium nitrate is used in
gunpowder (
black powder). An older term for KNO
3 is
saltpeter.
★
Potassium carbonate, known as
potash, is used in
glass manufacturing.
★
Glass treated with liquid potassium is much stronger than regular glass.
★ Potassium vapor is used in several types of
magnetometers.
★
NaK (usually pronounced "nack"), an
alloy of
sodium and potassium which is liquid at room temperature, is used as a heat-transfer medium. It can also be used as a
desiccant for producing dry and air-free solvents.
★ The
superoxide KO
2 is used as a portable source of oxygen and as a carbon dioxide absorber. It is useful in
portable respiration systems.
★
Potassium bromide (KBr) is used in photographic
film and in
engraving.
★
Potassium chromate (K
2CrO
4) is used in
dyes and
stains (bright yellowish-red colour), in
explosives and
fireworks, in safety
matches, in the tanning of
leather and in
fly paper.
★ Potassium fluorosilicate (K
2SiF
6) is used in specialized
glasses,
ceramics, and
enamels.
★ Potassium sodium tartrate, or
Rochelle salt (KNaC
4H
4O
6) is used in the
silvering of
mirrors.
Many potassium salts are very important, and include:
potassium bromide,
potassium carbonate,
potassium chlorate,
potassium chloride,
potassium chromate,
potassium cyanide,
potassium dichromate,
potassium iodide,
potassium nitrate,
potassium sulfate.
History
Potassium was discovered in
1807 by Sir
Humphry Davy, who derived it from
caustic potash (K
OH). Potassium was the first metal that was isolated by
electrolysis.
Potassium was not known in
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 ''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.
Occurrence
Potassium makes up about 1.5% of the weight of the
Earth's crust and is the seventh most abundant element in it. As it is very
electropositive, potassium metal is difficult to obtain from its
minerals. It is never found free in nature, as it reacts violently with water.
Potassium salts such as
carnallite,
langbeinite,
polyhalite, and
sylvite are found in ancient
lake and
sea beds. These minerals form extensive deposits in these environments, making extracting potassium and its salts more economical. The principal source of potassium,
potash, is mined in
Saskatchewan,
California,
Germany,
New Mexico,
Utah, and in other places around the world. 3000 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. See
Potash Corporation of Saskatchewan. The
oceans are another source of potassium, but the quantity present in a given volume of
seawater is relatively low compared with
sodium.
Potassium can be isolated through
electrolysis of its
hydroxide in a process that has changed little since
Davy. Thermal methods also are employed in potassium production, using
potassium chloride.
''See also .''
Isotopes
Main articles: isotopes of potassium
There are 24 known
isotopes of potassium. Three isotopes occur naturally:
39K (93.3%),
40K (0.0117%) and
41K (6.7%). Naturally occurring
40K decays to stable
40Ar (11.2%) by
electron capture and by
positron emission, and decays to stable
40Ca (88.8%) by
beta decay;
40K has a
half-life of 1.250×10
9 years.
The decay of
40K to
40Ar enables a commonly used method for dating rocks. The conventional
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.,
40Ar) was quantitatively retained.
Minerals are dated by measurement of the concentration of potassium and the amount of radiogenic
40Ar 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
tracers in studies of
weathering. They have also been used for
nutrient cycling studies because potassium is a
macronutrient required for
life.
40K 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,
40K represents the largest source of radioactivity, greater even than
14C. In a human body of 70 kg mass, about 4,400 nuclei of
40K decay per second.
[2]
The activity of natural potassium is 31
Bq/g.
Precautions
Peroxides (Yellow) and Ozonides (Red) on surface of potassium metal.
Solid potassium reacts violently with water, and should therefore be kept under a mineral oil such as
kerosene and handled with care. Unlike lithium and sodium however, potassium cannot be stored under oil indefinitely. If stored longer than 6 months to a year, dangerous shock-sensitive
peroxides 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.
[3]
The extremely alkaline
potassium hydroxide (KOH) residue on the surface of potassium which has been exposed to moisture, is a caustic hazard. As with sodium metal, the "soapy" feel of potassium metal on skin is due to caustic breakdown of the fats in skin into crude soft potassium
soap, and represents the beginning of an
alkali burn. Potassium should obviously be handled with care, with full skin and eye protection.
Potassium fires are exacerbated by water, and only a few dry chemicals are effective for them.
Potassium in nutrition and medicine
Potassium is an essential mineral
macronutrient 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.
Potassium is also important in allowing muscle contraction and the sending of all nerve impulses in animals. See
action potential for an explanation of the interplay of sodium and potassium in all excitable animal cells. Because of the interaction of the charge on a potassium ion and its surrounding water molecules, K
+ ions are actually a little larger than Na
+ ions, and ion channels and pumps in cell membranes can easily distinguish between the two types of ions, actively pumping or passively allowing one of the two ions to pass, while blocking the other.
A shortage of potassium in body fluids may cause a potentially fatal condition known as
hypokalemia (see article for detail), typically resulting from
diarrhoea, increased
diuresis and vomiting. Deficiency symptoms include muscle weakness, paralytic ileus, ECG abnormalities, decreased reflex response and (in severe cases) respiratory paralysis,
alkalosis and
arrhythmia.
Eating a variety of foods that contain potassium is the best way to get an adequate amount. Healthy individuals who eat a balanced diet rarely need supplements. Foods with high sources of potassium include
broccoli,
orange juice,
potatoes,
bananas,
soybeans,
avocados,
apricots,
pomegranates,
parsnips and
turnips, although many other
fruits,
vegetables, and
meats contain potassium. Research has indicated that diets high in potassium can reduce the risk of
hypertension.
The
2004 guidelines of the
Institute of Medicine specify an
RDA of 4,000mg of potassium. However, it is thought that most Americans consume only half that amount per day . Similarly, in the
European Union, particularly in
Germany and
Italy, insufficient potassium intake is widespread (
[1]).
Supplements of potassium in medicine are most widely used in conjunction with
loop diuretics and
thiazides, 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.
Some people with
kidney disease are advised to avoid large quantities of dietary potassium.
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.
See also
★
★
Potassium in biology
★
Fictional applications of real materials
References
★
Los Alamos National Laboratory – Potassium
1. Biology, , Neil, Campbell, , ,
2. background radiation - potassium-40 - γ radiation
3. DANGER: PEROXIDIZABLE CHEMICALS Thomas K. Wray
External links
★
WebElements.com – Potassium
العربية
ä¸å›½
Français
Deutsch
Ελληνική
हिनà¥à¤¦à¥€
Italiano
日本語
Português
РуÑÑкий
Español
