Potassium Tetrafluoroborate
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Potassium is the
chemical element A chemical element is a species of atoms that have a given number of protons in their nuclei, including the pure substance consisting only of that species. Unlike chemical compounds, chemical elements cannot be broken down into simpler sub ...
with the
symbol A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, or relationship. Symbols allow people to go beyond what is known or seen by creating linkages between otherwise very different conc ...
K (from
Neo-Latin New Latin (also called Neo-Latin or Modern Latin) is the revival of Literary Latin used in original, scholarly, and scientific works since about 1500. Modern scholarly and technical nomenclature, such as in zoological and botanical taxonomy ...
''
kalium Potassium is the chemical element with the symbol K (from Neo-Latin '' kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...
'') and
atomic number The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei, this is equal to the proton number (''n''p) or the number of protons found in the nucleus of every ...
19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmospheric
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
to form flaky white
potassium peroxide Potassium peroxide is an inorganic compound with the molecular formula K2O2. It is formed as potassium reacts with oxygen in the air, along with potassium oxide (K2O) and potassium superoxide (KO2). Potassium peroxide reacts with water to form p ...
in only seconds of exposure. It was first isolated from
potash Potash () includes various mined and manufactured salts that contain potassium in water-soluble form.
, the ashes of plants, from which its name derives. In the
periodic table The periodic table, also known as the periodic table of the (chemical) elements, is a rows and columns arrangement of the chemical elements. It is widely used in chemistry, physics, and other sciences, and is generally seen as an icon of ch ...
, potassium is one of the
alkali metal The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K),The symbols Na and K for sodium and potassium are derived from their Latin names, ''natrium'' and ''kalium''; these are still the origins of the names ...
s, all of which have a single
valence electron In chemistry and physics, a valence electron is an electron in the outer shell associated with an atom, and that can participate in the formation of a chemical bond if the outer shell is not closed. In a single covalent bond, a shared pair forms ...
in the outer electron shell, that is easily removed to create an ion with a positive charge – a
cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
, that combines with
anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
s to form
salts In chemistry, a salt is a chemical compound consisting of an ionic assembly of positively charged cations and negatively charged anions, which results in a compound with no net electric charge. A common example is table salt, with positively cha ...
. Potassium in nature occurs only in ionic salts. Elemental potassium reacts vigorously with water, generating sufficient heat to ignite
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
emitted in the reaction, and burning with a
lilac ''Syringa'' is a genus of 12 currently recognized species of flowering plant, flowering woody plants in the olive family or Oleaceae called lilacs. These lilacs are native to woodland and scrub from southeastern Europe to eastern Asia, and wid ...
- colored flame. It is found dissolved in sea water (which is 0.04% potassium by weight), and occurs in many
mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. ( ...
s such as
orthoclase Orthoclase, or orthoclase feldspar (endmember formula K Al Si3 O8), is an important tectosilicate mineral which forms igneous rock. The name is from the Ancient Greek for "straight fracture," because its two cleavage planes are at right angles t ...
, a common constituent of
granite Granite () is a coarse-grained (phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies undergro ...
s and other
igneous rock Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main The three types of rocks, rock types, the others being Sedimentary rock, sedimentary and metamorphic rock, metamorphic. Igneous rock ...
s. Potassium is chemically very similar to
sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...
, the previous element in group 1 of the periodic table. They have a similar first
ionization energy Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule i ...
, which allows for each atom to give up its sole outer electron. It was suspected in 1702 that they were distinct elements that combine with the same
anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
s to make similar salts, and this was proven in 1807 through using
electrolysis In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from n ...
. Naturally occurring potassium is composed of three
isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbers) ...
s, of which is
radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consid ...
. Traces of are found in all potassium, and it is the most common
radioisotope A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transferr ...
in the human body. Potassium ions are vital for the functioning of all living cells. The transfer of potassium ions across nerve cell membranes is necessary for normal nerve transmission; potassium deficiency and excess can each result in numerous signs and symptoms, including an abnormal heart rhythm and various
electrocardiographic Electrocardiography is the process of producing an electrocardiogram (ECG or EKG), a recording of the heart's electrical activity. It is an electrogram of the heart which is a graph of voltage versus time of the electrical activity of the hear ...
abnormalities. Fresh fruits and vegetables are good dietary sources of potassium. The body responds to the influx of dietary potassium, which raises serum potassium levels, with a shift of potassium from outside to inside cells and an increase in potassium excretion by the kidneys. Most industrial applications of potassium exploit the high
solubility In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubil ...
in water of potassium compounds, such as
potassium Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...
soap Soap is a salt of a fatty acid used in a variety of cleansing and lubricating products. In a domestic setting, soaps are surfactants usually used for washing, bathing, and other types of housekeeping. In industrial settings, soaps are use ...
s. Heavy crop production rapidly depletes the soil of potassium, and this can be remedied with agricultural fertilizers containing potassium, accounting for 95% of global potassium chemical production. Greenwood, p. 73


Etymology

The English name for the element ''potassium'' comes from the word ''
potash Potash () includes various mined and manufactured salts that contain potassium in water-soluble form.
'', which refers to an early method of extracting various potassium salts: placing in a ''pot'' the ''ash'' of burnt wood or tree leaves, adding water, heating, and evaporating the solution. When
Humphry Davy Sir Humphry Davy, 1st Baronet, (17 December 177829 May 1829) was a British chemist and inventor who invented the Davy lamp and a very early form of arc lamp. He is also remembered for isolating, by using electricity, several elements for t ...
first isolated the pure element using
electrolysis In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from n ...
in 1807, he named it ''potassium'', which he derived from the word ''potash''. The symbol ''K'' stems from ''kali'', itself from the root word ''
alkali In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a ...
'', which in turn comes from ar, القَلْيَه ''al-qalyah'' 'plant ashes'. In 1797, the German chemist
Martin Klaproth Martin Heinrich Klaproth (1 December 1743 – 1 January 1817) was a German chemist. He trained and worked for much of his life as an apothecary, moving in later life to the university. His shop became the second-largest apothecary in Berlin, and ...
discovered "potash" in the minerals
leucite Leucite is a rock-forming mineral of the feldspathoid group, silica-undersaturated and composed of potassium and aluminium tectosilicate KAlSi2O6. Crystals have the form of cubic icositetrahedra but, as first observed by Sir David Brewster in 18 ...
and
lepidolite Lepidolite is a lilac-gray or rose-colored member of the mica group of minerals with chemical formula . It is the most abundant lithium-bearing mineral and is a secondary source of this metal. It is the major source of the alkali metal rubidium. ...
, and realized that "potash" was not a product of plant growth but actually contained a new element, which he proposed calling ''kali''. In 1807, Humphry Davy produced the element via electrolysis: in 1809,
Ludwig Wilhelm Gilbert Ludwig Wilhelm Gilbert (12 August 1769 – 7 March 1824) was a German physicist and chemist, and professor of physics at the University of Leipzig. From 1799-1824 he published the "''Annalen der Physik''", of which Poggendorffs "''Annalen de ...
proposed the name ''Kalium'' for Davy's "potassium". In 1814, the Swedish chemist Berzelius advocated the name ''kalium'' for potassium, with the chemical symbol ''K''. The English and French-speaking countries adopted Davy and Gay-Lussac/Thénard's name ''Potassium'', whereas the Germanic countries adopted Gilbert/Klaproth's name ''Kalium''. The "Gold Book" of the
International Union of Pure and Applied Chemistry The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...
has designated the official chemical symbol as K.


Properties


Physical

Potassium is the second least dense metal after
lithium Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid el ...
. It is a soft solid with a low
melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends ...
, and can be easily cut with a knife. Freshly cut potassium is silvery in appearance, but it begins to tarnish toward gray immediately on exposure to air. Greenwood, p. 76 In a
flame test A flame test is an analytical procedure used in chemistry to detect the presence of certain elements, primarily metal ions, based on each element's characteristic flame emission spectrum (which may be affected by the presence of chloride ion ...
, potassium and its compounds emit a lilac color with a peak emission wavelength of 766.5 nanometers. Neutral potassium atoms have 19 electrons, one more than the configuration of the
noble gas The noble gases (historically also the inert gases; sometimes referred to as aerogens) make up a class of chemical elements with similar properties; under standard conditions, they are all odorless, colorless, monatomic gases with very low chemi ...
argon Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abu ...
. Because of its low first
ionization energy Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule i ...
of 418.8kJ/mol, the potassium atom is much more likely to lose the last electron and acquire a positive charge, although negatively charged
alkalide An alkalide is a chemical compound in which alkali metal atoms are anions (negative ions) with a charge or oxidation state of −1. Until the first discovery of alkalides in the 1970s, alkali metals were known to appear in salts only as cations ...
ions are not impossible. In contrast, the second ionization energy is very high (3052kJ/mol).


Chemical

Potassium reacts with oxygen, water, and carbon dioxide components in air. With oxygen it forms
potassium peroxide Potassium peroxide is an inorganic compound with the molecular formula K2O2. It is formed as potassium reacts with oxygen in the air, along with potassium oxide (K2O) and potassium superoxide (KO2). Potassium peroxide reacts with water to form p ...
. With water potassium forms
potassium hydroxide Potassium hydroxide is an inorganic compound with the formula K OH, and is commonly called caustic potash. Along with sodium hydroxide (NaOH), KOH is a prototypical strong base. It has many industrial and niche applications, most of which exp ...
. The reaction of potassium with water can be violently
exothermic In thermodynamics, an exothermic process () is a thermodynamic process or reaction that releases energy from the system to its surroundings, usually in the form of heat, but also in a form of light (e.g. a spark, flame, or flash), electricity (e ...
, especially since the coproduced
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
gas can ignite. Because of this, potassium and the liquid sodium-potassium (
NaK In data networking, telecommunications, and computer buses, an acknowledgment (ACK) is a signal that is passed between communicating processes, computers, or devices to signify acknowledgment, or receipt of message, as part of a communicatio ...
) alloy are potent
desiccant A desiccant is a hygroscopic substance that is used to induce or sustain a state of dryness (desiccation) in its vicinity; it is the opposite of a humectant. Commonly encountered pre-packaged desiccants are solids that absorb water. Desiccant ...
s, although they are no longer used as such.


Compounds

Four oxides of potassium are well studied:
potassium oxide Potassium oxide ( K O) is an ionic compound of potassium and oxygen. It is a base. This pale yellow solid is the simplest oxide of potassium. It is a highly reactive compound that is rarely encountered. Some industrial materials, such as fertiliz ...
(),
potassium peroxide Potassium peroxide is an inorganic compound with the molecular formula K2O2. It is formed as potassium reacts with oxygen in the air, along with potassium oxide (K2O) and potassium superoxide (KO2). Potassium peroxide reacts with water to form p ...
(),
potassium superoxide Potassium superoxide is an inorganic compound with the formula KO2. It is a yellow paramagnetic solid that decomposes in moist air. It is a rare example of a stable salt of the superoxide anion. It is used as a scrubber, dehumidifier, and gen ...
() and
potassium ozonide Potassium ozonide is an oxygen rich compound of potassium. It is an ozonide, meaning it contains the ozonide anion (O3−). In polarized light, it shows pleochroism. Hybrid functional calculations have predicted the compound is an insulator with a ...
(). The binary potassium-oxygen compounds react with water forming
potassium hydroxide Potassium hydroxide is an inorganic compound with the formula K OH, and is commonly called caustic potash. Along with sodium hydroxide (NaOH), KOH is a prototypical strong base. It has many industrial and niche applications, most of which exp ...
KOH. Potassium hydroxide is a
strong base In chemistry, there are three definitions in common use of the word base, known as Arrhenius bases, Brønsted bases, and Lewis bases. All definitions agree that bases are substances that react with acids, as originally proposed by G.-F. Rou ...
. Illustrating its
hydrophilic A hydrophile is a molecule or other molecular entity that is attracted to water molecules and tends to be dissolved by water.Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon'' Oxford: Clarendon Press. In contrast, hydrophobes are no ...
character, as much as 1.21 kg of KOH can dissolve in a single liter of water. Anhydrous KOH is rarely encountered. KOH reacts readily with
carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
to produce
potassium carbonate Potassium carbonate is the inorganic compound with the formula K2 CO3. It is a white salt, which is soluble in water. It is deliquescent, often appearing as a damp or wet solid. Potassium carbonate is mainly used in the production of soap and gl ...
, and in principle could be used to remove traces of the gas from air. Like the closely related sodium hydroxide, potassium hydroxide reacts with
fat In nutrition science, nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such chemical compound, compounds, most commonly those that occur in living beings or in food. The term often refers spec ...
s to produce
soap Soap is a salt of a fatty acid used in a variety of cleansing and lubricating products. In a domestic setting, soaps are surfactants usually used for washing, bathing, and other types of housekeeping. In industrial settings, soaps are use ...
s. In general, potassium compounds are ionic and, owing to the high hydration energy of the ion, have excellent water solubility. The main species in water solution are the aquo complexes where ''n'' = 6 and 7.Lincoln, S. F.; Richens, D. T. and Sykes, A. G. "Metal Aqua Ions" in J. A. McCleverty and T. J. Meyer (eds.
''Comprehensive Coordination Chemistry II''
Vol. 1, pp. 515–555, .
Potassium heptafluorotantalate Potassium heptafluorotantalate is an inorganic compound with the formula K2 aF7 It is the potassium salt of the heptafluorotantalate anion aF7sup>2−. This white, water-soluble solid is an intermediate in the purification of tantalum from its o ...
is an intermediate in the purification of
tantalum Tantalum is a chemical element with the symbol Ta and atomic number 73. Previously known as ''tantalium'', it is named after Tantalus, a villain in Greek mythology. Tantalum is a very hard, ductile, lustrous, blue-gray transition metal that is ...
from the otherwise persistent contaminant of
niobium Niobium is a chemical element with chemical symbol Nb (formerly columbium, Cb) and atomic number 41. It is a light grey, crystalline, and ductile transition metal. Pure niobium has a Mohs hardness rating similar to pure titanium, and it has sim ...
.
Organopotassium compound Organosodium chemistry is the chemistry of organometallic compounds containing a carbon to sodium chemical bond. The application of organosodium compounds in chemistry is limited in part due to competition from organolithium compounds, which are ...
s illustrate nonionic compounds of potassium. They feature highly
polar Polar may refer to: Geography Polar may refer to: * Geographical pole, either of two fixed points on the surface of a rotating body or planet, at 90 degrees from the equator, based on the axis around which a body rotates * Polar climate, the c ...
covalent A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atoms ...
K–C bonds. Examples include
benzyl potassium Benzylpotassium is an organopotassium compound with the formula C6H5CH2K. It is an orange powder. Like organo-alkali metal reagents in general, benzyl potassium is highly reactive, so much so that it reacts with most solvents. It is highly air s ...
. Potassium
intercalate Intercalation may refer to: *Intercalation (chemistry), insertion of a molecule (or ion) into layered solids such as graphite * Intercalation (timekeeping), insertion of a leap day, week or month into some calendar years to make the calendar foll ...
s into
graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on large ...
to give a variety of
graphite intercalation compounds Graphite intercalation compounds are complex materials having a formula where the ion or is inserted ( intercalated) between the oppositely charged carbon layers. Typically ''m'' is much less than 1. These materials are deeply colored solids t ...
, including .


Isotopes

There are 25 known
isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbers) ...
s of potassium, three of which occur naturally: (93.3%), (0.0117%), and (6.7%) (by mole fraction). Naturally occurring has a
half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ato ...
of 1.250×109 years. It decays to stable by
electron capture Electron capture (K-electron capture, also K-capture, or L-electron capture, L-capture) is a process in which the proton-rich nucleus of an electrically neutral atom absorbs an inner atomic electron, usually from the K or L electron shells. Thi ...
or
positron emission Positron emission, beta plus decay, or β+ decay is a subtype of radioactive decay called beta decay, in which a proton inside a radionuclide nucleus is converted into a neutron while releasing a positron and an electron neutrino (). Positron ...
(11.2%) or to stable by
beta decay In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For ...
(88.8%). The decay of to is the basis of a common 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 () was quantitatively retained.
Mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. ( ...
s are dated by measurement of the concentration of potassium and the amount of radiogenic that has accumulated. The minerals best suited for dating include
biotite Biotite is a common group of phyllosilicate minerals within the mica group, with the approximate chemical formula . It is primarily a solid-solution series between the iron-endmember annite, and the magnesium-endmember phlogopite; more alumino ...
,
muscovite Muscovite (also known as common mica, isinglass, or potash mica) is a hydrated phyllosilicate mineral of aluminium and potassium with formula K Al2(Al Si3 O10)( F,O H)2, or ( KF)2( Al2O3)3( SiO2)6( H2O). It has a highly perfect basal cleavage ...
,
metamorphic Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causin ...
hornblende Hornblende is a complex inosilicate series of minerals. It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole. Hornblende minerals are common in igneous and metamorphic rocks ...
, and volcanic
feldspar Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) feldsp ...
; whole rock samples from volcanic flows and shallow instrusives can also be dated if they are unaltered. Apart from dating, potassium isotopes have been used as
tracers Tracer may refer to: Science * Flow tracer, any fluid property used to track fluid motion * Fluorescent tracer, a substance such as 2-NBDG containing a fluorophore that is used for tracking purposes * Histochemical tracer, a substance used for tr ...
in studies of
weathering Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little or no movement), ...
and for
nutrient cycling A nutrient cycle (or ecological recycling) is the movement and exchange of inorganic and organic matter back into the production of matter. Energy flow is a unidirectional and noncyclic pathway, whereas the movement of mineral nutrients is cycli ...
studies because potassium is a
macronutrient A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...
required for
life Life is a quality that distinguishes matter that has biological processes, such as signaling and self-sustaining processes, from that which does not, and is defined by the capacity for growth, reaction to stimuli, metabolism, energ ...
on Earth. 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. is the radioisotope with the largest abundance in the body. In healthy animals and people, represents the largest source of radioactivity, greater even than . In a human body of 70 kg, about 4,400 nuclei of decay per second. The activity of natural potassium is 31 Bq/g.


Cosmic formation and distribution

Potassium is formed in
supernova A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when ...
e by
nucleosynthesis Nucleosynthesis is the process that creates new atomic nuclei from pre-existing nucleons (protons and neutrons) and nuclei. According to current theories, the first nuclei were formed a few minutes after the Big Bang, through nuclear reactions in ...
from lighter atoms. Potassium is principally created in Type II supernovae via an explosive oxygen-burning process. (These are
fusion Fusion, or synthesis, is the process of combining two or more distinct entities into a new whole. Fusion may also refer to: Science and technology Physics *Nuclear fusion, multiple atomic nuclei combining to form one or more different atomic nucl ...
reactions; do not confuse with chemical burning between potassium and oxygen.) is also formed in
s-process The slow neutron-capture process, or ''s''-process, is a series of reactions in nuclear astrophysics that occur in stars, particularly asymptotic giant branch stars. The ''s''-process is responsible for the creation (nucleosynthesis) of approximat ...
nucleosynthesis and the
neon burning process The neon-burning process is a set of nuclear fusion reactions that take place in evolved massive stars with at least 8 Solar masses. Neon burning requires high temperatures and densities (around 1.2×109 K or 100 keV and 4×109 kg/m3). At such h ...
. Potassium is the 20th most abundant element in the solar system and the 17th most abundant element by weight in the Earth. It makes up about 2.6% of the weight of the
Earth's crust Earth's crust is Earth's thin outer shell of rock, referring to less than 1% of Earth's radius and volume. It is the top component of the lithosphere, a division of Earth's layers that includes the crust and the upper part of the mantle. The ...
and is the seventh most abundant element in the crust. The potassium concentration in seawater is 0.39g/L (0.039 wt/v%), about one twenty-seventh the concentration of sodium.


Potash

Potash is primarily a mixture of potassium salts because plants have little or no sodium content, and the rest of a plant's major mineral content consists of calcium salts of relatively low solubility in water. While potash has been used since ancient times, its composition was not understood.
Georg Ernst Stahl Georg Ernst Stahl (22 October 1659 – 24 May 1734) was a German chemist, physician and philosopher. He was a supporter of vitalism, and until the late 18th century his works on phlogiston were accepted as an explanation for chemical processes.Ku ...
obtained experimental evidence that led him to suggest the fundamental difference of sodium and potassium salts in 1702, and
Henri Louis Duhamel du Monceau Henri-Louis Duhamel du Monceau (20 July 1700, Paris13 August 1782, Paris), was a French physician, naval engineer and botanist. Biography Henri-Louis Duhamel du Monceau was born in Paris in 1700, the son of Alexandre Duhamel, lord of Denain ...
was able to prove this difference in 1736. The exact chemical composition of potassium and sodium compounds, and the status as chemical element of potassium and sodium, was not known then, and thus
Antoine Lavoisier Antoine-Laurent de Lavoisier ( , ; ; 26 August 17438 May 1794), When reduced without charcoal, it gave off an air which supported respiration and combustion in an enhanced way. He concluded that this was just a pure form of common air and th ...
did not include the alkali in his list of chemical elements in 1789. For a long time the only significant applications for potash were the production of glass, bleach, soap and
gunpowder Gunpowder, also commonly known as black powder to distinguish it from modern smokeless powder, is the earliest known chemical explosive. It consists of a mixture of sulfur, carbon (in the form of charcoal) and potassium nitrate (saltpeter). ...
as potassium nitrate. Potassium soaps from animal fats and vegetable oils were especially prized because they tend to be more water-soluble and of softer texture, and are therefore known as soft
soap Soap is a salt of a fatty acid used in a variety of cleansing and lubricating products. In a domestic setting, soaps are surfactants usually used for washing, bathing, and other types of housekeeping. In industrial settings, soaps are use ...
s. The discovery by
Justus Liebig Justus Freiherr von Liebig (12 May 1803 – 20 April 1873) was a German scientist who made major contributions to agricultural and biological chemistry, and is considered one of the principal founders of organic chemistry. As a professor at th ...
in 1840 that potassium is a necessary element for plants and that most types of soil lack potassium caused a steep rise in demand for potassium salts. Wood-ash from fir trees was initially used as a potassium salt source for fertilizer, but, with the discovery in 1868 of mineral deposits containing
potassium chloride Potassium chloride (KCl, or potassium salt) is a metal halide salt composed of potassium and chlorine. It is odorless and has a white or colorless vitreous crystal appearance. The solid dissolves readily in water, and its solutions have a salt ...
near
Staßfurt Staßfurt (Stassfurt) () is a town in the Salzlandkreis district, in Saxony-Anhalt, Germany. It is situated on both sides of the river Bode, approximately northeast of Aschersleben, and south of Magdeburg. Pop. (2005) 23,538. It was one of th ...
, Germany, the production of potassium-containing fertilizers began at an industrial scale. Other potash deposits were discovered, and by the 1960s Canada became the dominant producer.


Metal

Potassium ''metal'' was first isolated in 1807 by Humphry Davy, who derived it by electrolysis of molten KOH with the newly discovered
voltaic pile upright=1.2, Schematic diagram of a copper–zinc voltaic pile. The copper and zinc discs were separated by cardboard or felt spacers soaked in salt water (the electrolyte). Volta's original piles contained an additional zinc disk at the bottom, ...
. Potassium was the first metal that was isolated by electrolysis. Later in the same year, Davy reported extraction of the metal
sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...
from a mineral derivative (
caustic soda Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly caustic base and alka ...
, NaOH, or lye) rather than a plant salt, by a similar technique, demonstrating that the elements, and thus the salts, are different. Although the production of potassium and sodium metal should have shown that both are elements, it took some time before this view was universally accepted. Because of the sensitivity of potassium to water and air,
air-free technique Air-free techniques refer to a range of manipulations in the chemistry laboratory for the handling of compounds that are air-sensitive. These techniques prevent the compounds from reacting with components of air, usually water and oxygen; less comm ...
s are normally employed for handling the element. It is unreactive toward nitrogen and saturated hydrocarbons such as mineral oil or
kerosene Kerosene, paraffin, or lamp oil is a combustible hydrocarbon liquid which is derived from petroleum. It is widely used as a fuel in aviation as well as households. Its name derives from el, κηρός (''keros'') meaning "wax", and was regi ...
. It readily dissolves in liquid
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...
, up to 480 g per 1000 g of ammonia at 0°C. Depending on the concentration, the ammonia solutions are blue to yellow, and their electrical conductivity is similar to that of liquid metals. Potassium slowly reacts with ammonia to form , but this reaction is accelerated by minute amounts of transition metal salts. Burkhardt, p. 32 Because it can reduce the
salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...
s to the metal, potassium is often used as the reductant in the preparation of finely divided metals from their salts by the Rieke method. Illustrative is the preparation of magnesium: :


Geology

Elemental potassium does not occur in nature because of its high reactivity. It reacts violently with water (see section Precautions below) and also reacts with oxygen.
Orthoclase Orthoclase, or orthoclase feldspar (endmember formula K Al Si3 O8), is an important tectosilicate mineral which forms igneous rock. The name is from the Ancient Greek for "straight fracture," because its two cleavage planes are at right angles t ...
(potassium feldspar) is a common rock-forming mineral.
Granite Granite () is a coarse-grained (phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies undergro ...
for example contains 5% potassium, which is well above the average in the Earth's crust.
Sylvite Sylvite, or sylvine, is potassium chloride (KCl) in natural mineral form. It forms crystals in the isometric system very similar to normal rock salt, halite ( NaCl). The two are, in fact, isomorphous. Sylvite is colorless to white with shades of ...
(KCl),
carnallite Carnallite (also carnalite) is an evaporite mineral, a hydrated potassium magnesium chloride with formula KMgCl3·6(H2O). It is variably colored yellow to white, reddish, and sometimes colorless or blue. It is usually massive to fibrous with rare ...
(),
kainite Kainite ( or ) (KMg(SO4)Cl·3H2O) is an evaporite mineral in the class of "Sulfates (selenates, etc.) with additional anions, with H2O" according to the Nickel–Strunz classification. It is a hydrated potassium-magnesium sulfate-chloride, natura ...
() and
langbeinite Langbeinite is a potassium magnesium sulfate mineral with the chemical formula K2Mg2(SO4)3. Langbeinite crystallizes in the isometric-tetartoidal (cubic) system as transparent colorless or white with pale tints of yellow to green and violet cry ...
() are the minerals found in large
evaporite An evaporite () is a water-soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as ocea ...
deposits worldwide. The deposits often show layers starting with the least soluble at the bottom and the most soluble on top. Deposits of niter (
potassium nitrate Potassium nitrate is a chemical compound with the chemical formula . This alkali metal nitrate salt is also known as Indian saltpetre (large deposits of which were historically mined in India). It is an ionic salt of potassium ions K+ and nitrat ...
) are formed by decomposition of organic material in contact with atmosphere, mostly in caves; because of the good water solubility of niter the formation of larger deposits requires special environmental conditions.


Biological role

Potassium is the eighth or ninth most common element by mass (0.2%) in the human body, so that a 60kg adult contains a total of about 120g of potassium. The
body Body may refer to: In science * Physical body, an object in physics that represents a large amount, has mass or takes up space * Body (biology), the physical material of an organism * Body plan, the physical features shared by a group of anima ...
has about as much potassium as sulfur and chlorine, and only calcium and phosphorus are more abundant (with the exception of the ubiquitous
CHON CHON is a mnemonic acronym for the four most common elements in living organisms: carbon, hydrogen, oxygen, and nitrogen. The acronym CHNOPS, which stands for ''c''arbon, ''h''ydrogen, ''n''itrogen, ''o''xygen, ''p''hosphorus, ''s''ulfur, r ...
elements). Potassium ions are present in a wide variety of proteins and enzymes.


Biochemical function

Potassium levels influence multiple physiological processes, including *resting cellular-membrane potential and the propagation of action potentials in neuronal, muscular, and cardiac tissue. Due to the electrostatic and chemical properties, ions are larger than ions, and ion channels and pumps in cell membranes can differentiate between the two ions, actively pumping or passively passing one of the two ions while blocking the other. *hormone secretion and action *vascular tone *systemic blood pressure control *gastrointestinal motility *acid–base homeostasis *glucose and insulin metabolism *mineralocorticoid action *renal concentrating ability *fluid and electrolyte balance


Homeostasis

Potassium homeostasis denotes the maintenance of the total body potassium content, plasma potassium level, and the ratio of the intracellular to extracellular potassium concentrations within narrow limits, in the face of pulsatile intake (meals), obligatory renal excretion, and shifts between intracellular and extracellular compartments.


Plasma levels

Plasma potassium is normally kept at 3.5 to 5.5 millimoles (mmol)
r milliequivalents (mEq) R, or r, is the eighteenth letter of the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''ar'' (pronounced ), plural ''ars'', or in Irela ...
per liter by multiple mechanisms. Levels outside this range are associated with an increasing rate of death from multiple causes, and some cardiac, kidney, and lung diseases progress more rapidly if serum potassium levels are not maintained within the normal range. An average meal of 40–50mmol presents the body with more potassium than is present in all plasma (20–25mmol). However, this surge causes the plasma potassium to rise only 10% at most as a result of prompt and efficient clearance by both renal and extra-renal mechanisms.
Hypokalemia Hypokalemia is a low level of potassium (K+) in the blood serum. Mild low potassium does not typically cause symptoms. Symptoms may include feeling tired, leg cramps, weakness, and constipation. Low potassium also increases the risk of an abno ...
, a deficiency of potassium in the plasma, can be fatal if severe. Common causes are increased gastrointestinal loss (
vomiting Vomiting (also known as emesis and throwing up) is the involuntary, forceful expulsion of the contents of one's stomach through the mouth and sometimes the Human nose, nose. Vomiting can be the result of ailments like Food-poisoning, foo ...
,
diarrhea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin wi ...
), and increased renal loss (
diuresis Diuresis () is increased urination (polyuria) or, in the related word senses more often intended, the physiological process that produces such an increase or the administration of medications to encourage that process. It involves extra urine pro ...
). Deficiency symptoms include muscle weakness,
paralytic ileus Ileus is a disruption of the normal propulsive ability of the intestine. It can be caused by lack of peristalsis or by mechanical obstruction. The word 'ileus' is from Ancient Greek ''eileós'' (, "intestinal obstruction"). The term 'subileus' re ...
, ECG abnormalities, decreased reflex response; and in severe cases, respiratory paralysis,
alkalosis Alkalosis is the result of a process reducing hydrogen ion concentration of arterial blood plasma (alkalemia). In contrast to acidemia (serum pH 7.35 or lower), alkalemia occurs when the serum pH is higher than normal (7.45 or higher). Alkalosis i ...
, and
cardiac arrhythmia Arrhythmias, also known as cardiac arrhythmias, heart arrhythmias, or dysrhythmias, are irregularities in the heartbeat, including when it is too fast or too slow. A resting heart rate that is too fast – above 100 beats per minute in adults ...
.


Control mechanisms

Potassium content in the plasma is tightly controlled by four basic mechanisms, which have various names and classifications. The four are 1) a reactive negative-feedback system, 2) a reactive feed-forward system, 3) a predictive or
circadian A circadian rhythm (), or circadian cycle, is a natural, internal process that regulates the sleep–wake cycle and repeats roughly every 24 hours. It can refer to any process that originates within an organism (i.e., endogenous) and responds to ...
system, and 4) an internal or cell membrane transport system. Collectively, the first three are sometimes termed the "external potassium homeostasis system"; and the first two, the "reactive potassium homeostasis system". * The reactive negative-feedback system refers to the system that induces renal secretion of potassium in response to a rise in the plasma potassium (potassium ingestion, shift out of cells, or intravenous infusion.) * The reactive feed-forward system refers to an incompletely understood system that induces renal potassium secretion in response to potassium ingestion prior to any rise in the plasma potassium. This is probably initiated by gut cell potassium receptors that detect ingested potassium and trigger
vagal The vagus nerve, also known as the tenth cranial nerve, cranial nerve X, or simply CN X, is a cranial nerve that interfaces with the parasympathetic control of the heart, lungs, and digestive tract. It comprises two nerves—the left and right v ...
afferent signals to the pituitary gland. * The predictive or circadian system increases renal secretion of potassium during mealtime hours (e.g. daytime for humans, nighttime for rodents) independent of the presence, amount, or absence of potassium ingestion. It is mediated by a
circadian oscillator A circadian clock, or circadian oscillator, is a biochemical oscillator that cycles with a stable phase and is synchronized with solar time. Such a clock's ''in vivo'' period is necessarily almost exactly 24 hours (the earth's current solar day ...
in the
suprachiasmatic nucleus The suprachiasmatic nucleus or nuclei (SCN) is a tiny region of the brain in the hypothalamus, situated directly above the optic chiasm. It is responsible for controlling circadian rhythms. The neuronal and hormonal activities it generates regula ...
of the brain (central clock), which causes the kidney (peripheral clock) to secrete potassium in this rhythmic circadian fashion. * The ion transport system moves potassium across the cell membrane using two mechanisms. One is active and pumps sodium out of, and potassium into, the cell. The other is passive and allows potassium to leak out of the cell. Potassium and sodium cations influence fluid distribution between intracellular and extracellular compartments by
osmotic Osmosis (, ) is the spontaneous net movement or diffusion of solvent molecules through a selectively-permeable membrane from a region of high water potential (region of lower solute concentration) to a region of low water potential (region of ...
forces. The movement of potassium and sodium through the cell membrane is mediated by the Na⁺/K⁺-ATPase pump. This
ion pump An ion pump (also referred to as a sputter ion pump) is a type of vacuum pump which operates by sputtering a metal getter. Under ideal conditions, ion pumps are capable of reaching pressures as low as 10−11 mbar. An ion pump first ionizes ga ...
uses ATP to pump three sodium ions out of the cell and two potassium ions into the cell, creating an electrochemical gradient and electromotive force across the cell membrane. The highly selective
potassium ion channels Potassium channels are the most widely distributed type of ion channel found in virtually all organisms. They form potassium-selective ion channel#Basic features, pores that span cell membranes. Potassium channels are found in most cell (biology), ...
(which are
tetramer A tetramer () (''tetra-'', "four" + '' -mer'', "parts") is an oligomer formed from four monomers or subunits. The associated property is called ''tetramery''. An example from inorganic chemistry is titanium methoxide with the empirical formula Ti ...
s) are crucial for hyperpolarization inside
neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...
s after an action potential is triggered, to cite one example. The most recently discovered potassium ion channel is KirBac3.1, which makes a total of five potassium ion channels (KcsA, KirBac1.1, KirBac3.1, KvAP, and MthK) with a determined structure. All five are from
prokaryotic A prokaryote () is a Unicellular organism, single-celled organism that lacks a cell nucleus, nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek language, Greek wikt:πρό#Ancient Greek, πρό (, 'before') a ...
species.


Renal filtration, reabsorption, and excretion

Renal handling of potassium is closely connected to sodium handling. Potassium is the major cation (positive ion) inside animal cells 50mmol/L, (4.8g) while sodium is the major cation of
extracellular fluid In cell biology, extracellular fluid (ECF) denotes all body fluid outside the cells of any multicellular organism. Total body water in healthy adults is about 60% (range 45 to 75%) of total body weight; women and the obese typically have a lower ...
50mmol/L, (3.345g) In the kidneys, about 180liters of plasma is filtered through the
glomeruli ''Glomerulus'' () is a common term used in anatomy to describe globular structures of entwined vessels, fibers, or neurons. ''Glomerulus'' is the diminutive of the Latin ''glomus'', meaning "ball of yarn". ''Glomerulus'' may refer to: * the filter ...
and into the
renal tubules The nephron is the minute or microscopic structural and functional unit of the kidney. It is composed of a renal corpuscle and a renal tubule. The renal corpuscle consists of a tuft of capillaries called a glomerulus and a cup-shaped structure ca ...
per day. This filtering involves about 600g of sodium and 33g of potassium. Since only 1–10g of sodium and 1–4g of potassium are likely to be replaced by diet, renal filtering must efficiently reabsorb the remainder from the plasma. Sodium is reabsorbed to maintain extracellular volume, osmotic pressure, and serum sodium concentration within narrow limits. Potassium is reabsorbed to maintain serum potassium concentration within narrow limits.
Sodium pump Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable is ...
s in the renal tubules operate to reabsorb sodium. Potassium must be conserved, but because the amount of potassium in the blood plasma is very small and the pool of potassium in the cells is about 30 times as large, the situation is not so critical for potassium. Since potassium is moved passively in counter flow to sodium in response to an apparent (but not actual) Donnan equilibrium, 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 excreted twice and reabsorbed three times before the urine reaches the collecting tubules. At that point, urine usually has about the same potassium concentration as plasma. At the end of the processing, potassium is secreted one more time if the serum levels are too high. With no potassium intake, it is excreted at about 200mg per day until, in about a week, potassium in the serum declines to a mildly deficient level of 3.0–3.5mmol/L. If potassium is still withheld, the concentration continues to fall until a severe deficiency causes eventual death. The potassium moves passively through pores in the cell membrane. When ions move through
Ion transporter In biology, a transporter is a transmembrane protein that moves ions (or other small molecules) across a biological membrane to accomplish many different biological functions including, cellular communication, maintaining homeostasis, energy produc ...
s (pumps) there is a gate in the pumps on both sides of the cell membrane and only one gate can be open at once. As a result, approximately 100 ions are forced through per second.
Ion channel Ion channels are pore-forming membrane proteins that allow ions to pass through the channel pore. Their functions include establishing a resting membrane potential, shaping action potentials and other electrical signals by gating the flow of io ...
have only one gate, and there only one kind of ion can stream through, at 10 million to 100 million ions per second. Calcium is required to open the pores, although calcium may work in reverse by blocking at least one of the pores. Carbonyl groups inside the pore on the amino acids mimic the water hydration that takes place in water solution by the nature of the electrostatic charges on four carbonyl groups inside the pore.


Nutrition


Dietary recommendations

The U.S.
National Academy of Medicine The National Academy of Medicine (NAM), formerly called the Institute of Medicine (IoM) until 2015, is an American nonprofit, non-governmental organization. The National Academy of Medicine is a part of the National Academies of Sciences, En ...
(NAM), on behalf of both the U.S. and Canada, sets Estimated Average Requirements (EARs) and Recommended Dietary Allowances (RDAs), or
Adequate Intake The Dietary Reference Intake (DRI) is a system of nutrition recommendations from the National Academy of Medicine (NAM) of the National Academies (United States). It was introduced in 1997 in order to broaden the existing guidelines known as Reco ...
s (AIs) for when there is not sufficient information to set EARs and RDAs. Collectively the EARs, RDAs, AIs and ULs are referred to as
Dietary Reference Intake The Dietary Reference Intake (DRI) is a system of nutrition recommendations from the National Academy of Medicine (NAM) of the National Academies (United States). It was introduced in 1997 in order to broaden the existing guidelines known as Reco ...
s. For both males and females under 9 years of age, the AIs for potassium are: 400mg of potassium for 0-6-month-old infants, 860mg of potassium for 7-12-month-old infants, 2,000mg of potassium for 1-3-year-old children, and 2,300mg of potassium for 4-8-year-old children. For males 9 years of age and older, the AIs for potassium are: 2,500mg of potassium for 9-13-year-old males, 3,000mg of potassium for 14-18-year-old males, and 3,400mg for males that are 19 years of age and older. For females 9 years of age and older, the AIs for potassium are: 2,300mg of potassium for 9-18-year-old females, and 2,600mg of potassium for females that are 19 years of age and older. For pregnant and lactating females, the AIs for potassium are: 2,600mg of potassium for 14-18-year-old pregnant females, 2,900mg for pregnant females that are 19 years of age and older; furthermore, 2,500mg of potassium for 14-18-year-old lactating females, and 2,800mg for lactating females that are 19 years of age and older. As for safety, the NAM also sets
tolerable upper intake level The Dietary Reference Intake (DRI) is a system of nutrition recommendations from the National Academy of Medicine (NAM) of the National Academies (United States). It was introduced in 1997 in order to broaden the existing guidelines known as Reco ...
s (ULs) for vitamins and minerals, but for potassium the evidence was insufficient, so no UL was established. As of 2004, most Americans adults consume less than 3,000mg. Likewise, in the European Union, in particular in Germany, and Italy, insufficient potassium intake is somewhat common. The British National Health Service recommends a similar intake, saying that adults need 3,500mg per day and that excess amounts may cause health problems such as stomach pain and
diarrhea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin wi ...
. In 2019, the
National Academies of Sciences, Engineering, and Medicine The National Academies of Sciences, Engineering, and Medicine (also known as NASEM or the National Academies) are the collective scientific national academy of the United States. The name is used interchangeably in two senses: (1) as an umbrell ...
revised the Adequate Intake for potassium to 2,600 mg/day for females 19 years of age and older who are not pregnant or lactating, and 3,400 mg/day for males 19 years of age and older.


Food sources

Potassium is present in all fruits, vegetables, meat and fish. Foods with high potassium concentrations include yam,
parsley Parsley, or garden parsley (''Petroselinum crispum'') is a species of flowering plant in the family Apiaceae that is native to the central and eastern Mediterranean region (Sardinia, Lebanon, Israel, Cyprus, Turkey, southern Italy, Greece, Por ...
, dried
apricot An apricot (, ) is a fruit, or the tree that bears the fruit, of several species in the genus ''Prunus''. Usually, an apricot is from the species '' P. armeniaca'', but the fruits of the other species in ''Prunus'' sect. ''Armeniaca'' are also ...
s, milk, chocolate, all nut (fruit), nuts (especially almonds and pistachios), potatoes, bamboo shoots, bananas, avocados, coconut water, soybeans, and bran. The United States Department of Agriculture, USDA lists tomato paste, orange juice, beet greens, white beans, potatoes, Cooking banana, plantains, bananas, apricots, and many other dietary sources of potassium, ranked in descending order according to potassium content. A day's worth of potassium is in 5 plantains or 11 bananas.


Deficient intake

Diets low in potassium can lead to hypertension and hypokalemia.


Supplementation

Supplements of potassium are most widely used in conjunction with diuretics that block reabsorption of sodium and water upstream from the distal tubule (thiazides and loop diuretics), because this promotes increased distal tubular potassium secretion, with resultant increased potassium excretion. A variety of prescription and over-the counter supplements are available. Potassium chloride may be dissolved in water, but the salty/bitter taste makes liquid supplements unpalatable. Typical doses range from 10mmol (400mg), to 20mmol (800mg). Potassium is also available in tablets or capsules, which are formulated to allow potassium to leach slowly out of a matrix, since very high concentrations of potassium ion that occur adjacent to a solid tablet can injure the gastric or intestinal mucosa. For this reason, non-prescription potassium pills are limited by law in the US to a maximum of 99mg of potassium. A meta-analysis concluded that a 1640mg increase in the daily intake of potassium was associated with a 21% lower risk of stroke. Potassium chloride and potassium bicarbonate may be useful to control mild hypertension. In 2020, potassium was the 33rd most commonly prescribed medication in the United States, with more than 17million prescriptions.


Detection by taste buds

Potassium can be detected by taste because it triggers three of the five types of taste sensations, according to concentration. Dilute solutions of potassium ions 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 solutions makes high-dose potassium supplementation by liquid drinks a palatability challenge.


Commercial production


Mining

Potassium salts such as
carnallite Carnallite (also carnalite) is an evaporite mineral, a hydrated potassium magnesium chloride with formula KMgCl3·6(H2O). It is variably colored yellow to white, reddish, and sometimes colorless or blue. It is usually massive to fibrous with rare ...
,
langbeinite Langbeinite is a potassium magnesium sulfate mineral with the chemical formula K2Mg2(SO4)3. Langbeinite crystallizes in the isometric-tetartoidal (cubic) system as transparent colorless or white with pale tints of yellow to green and violet cry ...
, polyhalite, and sylvite form extensive
evaporite An evaporite () is a water-soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as ocea ...
deposits in ancient lake bottoms and seabeds, making extraction of potassium salts in these environments commercially viable. The principal source of potassium –
potash Potash () includes various mined and manufactured salts that contain potassium in water-soluble form.
– is mined in Canada, Russia, Belarus, Kazakhstan, Germany, Israel, United States, Jordan, and other places around the world. The first mined deposits were located near Staßfurt, Germany, but the deposits span from Great Britain over Germany into Poland. They are located in the Zechstein and were deposited in the Middle to Late Permian. The largest deposits ever found lie below the surface of the Canadian province of Saskatchewan. The deposits are located in the Elk Point Group produced in the Middle Devonian. Saskatchewan, where several large mines have operated since the 1960s pioneered the technique of freezing of wet sands (the Blairmore formation) to drive mine shafts through them. The main potash mining company in Saskatchewan until its merge was the Potash Corporation of Saskatchewan, now Nutrien. The water of the Dead Sea is used by Israel and Jordan as a source of potash, while the concentration in normal oceans is too low for commercial production at current prices.


Chemical extraction

Several methods are used to separate potassium salts from sodium and magnesium compounds. The most-used method is fractional precipitation using the solubility differences of the salts. Electrostatic separation of the ground salt mixture is also used in some mines. The resulting sodium and magnesium waste is either stored underground or piled up in slag heaps. Most of the mined potassium mineral ends up as
potassium chloride Potassium chloride (KCl, or potassium salt) is a metal halide salt composed of potassium and chlorine. It is odorless and has a white or colorless vitreous crystal appearance. The solid dissolves readily in water, and its solutions have a salt ...
after processing. The mineral industry refers to potassium chloride either as potash, muriate of potash, or simply MOP. Pure potassium metal can be isolated by
electrolysis In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from n ...
of its potassium hydroxide, hydroxide in a process that has changed little since it was first used by Humphry Davy in 1807. Although the electrolysis process was developed and used in industrial scale in the 1920s, the thermal method by reacting sodium with
potassium chloride Potassium chloride (KCl, or potassium salt) is a metal halide salt composed of potassium and chlorine. It is odorless and has a white or colorless vitreous crystal appearance. The solid dissolves readily in water, and its solutions have a salt ...
in a chemical equilibrium reaction became the dominant method in the 1950s. :Na + KCl → NaCl + K The production of NaK, sodium potassium alloys is accomplished by changing the reaction time and the amount of sodium used in the reaction. The Griesheimer process employing the reaction of potassium fluoride with calcium carbide was also used to produce potassium. : reagent, Reagent-grade potassium metal costs about $10.00/pound (mass), pound ($22/kg) in 2010 when purchased by the tonne. Lower purity metal is considerably cheaper. The market is volatile because long-term storage of the metal is difficult. It must be stored in a dry inert gas atmosphere or anhydrous mineral oil to prevent the formation of a surface layer of
potassium superoxide Potassium superoxide is an inorganic compound with the formula KO2. It is a yellow paramagnetic solid that decomposes in moist air. It is a rare example of a stable salt of the superoxide anion. It is used as a scrubber, dehumidifier, and gen ...
, a pressure-sensitive explosive that Detonation, detonates when scratched. The resulting explosion often starts a fire difficult to extinguish.


Cation identification

Potassium is now quantified by ionization techniques, but at one time it was quantitated by gravimetric analysis. Reagents used to precipitate potassium salts include sodium tetraphenylborate, hexachloroplatinic acid, and sodium cobaltinitrite into respectively potassium tetraphenylborate, potassium hexachloroplatinate, and potassium cobaltinitrite. The reaction with sodium cobaltinitrite is illustrative: : The potassium cobaltinitrite is obtained as a yellow solid.


Commercial uses


Fertilizer

Potassium ions are an essential component of plant nutrition and are found in most soil types. They are used as a fertilizer in agriculture, horticulture, and hydroponic culture in the form of potassium chloride, chloride (KCl), potassium sulfate, sulfate (), or potassium nitrate, nitrate (), representing the 'K' labeling of fertilizer, in 'NPK'. Agricultural fertilizers consume 95% of global potassium chemical production, and about 90% of this potassium is supplied as KCl. The potassium content of most plants ranges from 0.5% to 2% of the harvested weight of crops, conventionally expressed as amount of . Modern high-Crop yield, yield agriculture depends upon fertilizers to replace the potassium lost at harvest. Most agricultural fertilizers contain potassium chloride, while potassium sulfate is used for chloride-sensitive crops or crops needing higher sulfur content. The sulfate is produced mostly by decomposition of the complex minerals
kainite Kainite ( or ) (KMg(SO4)Cl·3H2O) is an evaporite mineral in the class of "Sulfates (selenates, etc.) with additional anions, with H2O" according to the Nickel–Strunz classification. It is a hydrated potassium-magnesium sulfate-chloride, natura ...
() and
langbeinite Langbeinite is a potassium magnesium sulfate mineral with the chemical formula K2Mg2(SO4)3. Langbeinite crystallizes in the isometric-tetartoidal (cubic) system as transparent colorless or white with pale tints of yellow to green and violet cry ...
(). Only a very few fertilizers contain potassium nitrate. In 2005, about 93% of world potassium production was consumed by the fertilizer industry. Furthermore, potassium can play a key role in nutrient cycling by controlling litter composition.


Medical use


Potassium citrate

Potassium citrate is used to treat a kidney stone condition called renal tubular acidosis.


Potassium chloride

Potassium, in the form of
potassium chloride Potassium chloride (KCl, or potassium salt) is a metal halide salt composed of potassium and chlorine. It is odorless and has a white or colorless vitreous crystal appearance. The solid dissolves readily in water, and its solutions have a salt ...
is used as a medication to treat and prevent low blood potassium. Low blood potassium may occur due to
vomiting Vomiting (also known as emesis and throwing up) is the involuntary, forceful expulsion of the contents of one's stomach through the mouth and sometimes the Human nose, nose. Vomiting can be the result of ailments like Food-poisoning, foo ...
,
diarrhea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin wi ...
, or certain medications. It is given by intravenous infusion, slow injection into a vein or by mouth.


Food additives

Potassium sodium tartrate (, Rochelle salt) is a main constituent of some varieties of baking powder; it is also used in the silvering of mirrors. Potassium bromate () is a strong oxidizer (E924), used to improve dough strength and rise height. Potassium bisulfite () 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 leathers.


Industrial

Major potassium chemicals are potassium hydroxide, potassium carbonate, potassium sulfate, and potassium chloride. Megatons of these compounds are produced annually. Potassium hydroxide KOH is a strong base, which is used in industry to neutralize strong and weak acids, to control pH and to manufacture potassium salt (chemistry), salts. It is also used to saponification, saponify
fat In nutrition science, nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such chemical compound, compounds, most commonly those that occur in living beings or in food. The term often refers spec ...
s and oils, in industrial cleaners, and in hydrolysis reactions, for example of esters. Potassium nitrate () or saltpeter is obtained from natural sources such as guano and evaporites or manufactured via the Haber process; it is the oxidant in
gunpowder Gunpowder, also commonly known as black powder to distinguish it from modern smokeless powder, is the earliest known chemical explosive. It consists of a mixture of sulfur, carbon (in the form of charcoal) and potassium nitrate (saltpeter). ...
(black powder) and an important agricultural fertilizer. Potassium cyanide (KCN) is used industrially to dissolve copper and precious metals, in particular silver and gold, by forming complex (chemistry), complexes. Its applications include gold mining, electroplating, and electroforming of these metals; it is also used in organic synthesis to make nitriles. Potassium carbonate ( or potash) is used in the manufacture of glass, soap, color TV tubes, fluorescent lamps, textile dyes and pigments. Potassium permanganate () is an oxidizing, bleaching and purification substance and is used for production of saccharin. Potassium chlorate () is added to matches and explosives. Potassium bromide (KBr) was formerly used as a sedative and in photography. While potassium chromate () is used in the manufacture of a host of different commercial products such as inks, dyes, wood stains (by reacting with the tannic acid in wood), explosives, fireworks, fly paper, and safety matches, as well as in the tanning of leather, all of these uses are due to the chemistry of the chromate ion rather than to that of the potassium ion.


Niche uses

There are thousands of uses of various potassium compounds. One example is
potassium superoxide Potassium superoxide is an inorganic compound with the formula KO2. It is a yellow paramagnetic solid that decomposes in moist air. It is a rare example of a stable salt of the superoxide anion. It is used as a scrubber, dehumidifier, and gen ...
, , an orange solid that acts as a portable source of oxygen and a carbon dioxide absorber. It is widely used in Rebreather#Rebreathers using an absorbent that releases oxygen, respiration systems in mines, submarines and spacecraft as it takes less volume than the gaseous oxygen. : Another example is potassium cobaltinitrite, , which is used as artist's pigment under the name of Aureolin or Cobalt Yellow. The stable isotopes of potassium can be Laser cooling, laser cooled and used to probe fundamental and Quantum technology, technological problems in Quantum mechanics, quantum physics. The two bosonic isotopes possess convenient Feshbach resonances to enable studies requiring tunable interactions, while is one of only two stable fermions amongst the alkali metals.


Laboratory uses

An alloy of sodium and potassium,
NaK In data networking, telecommunications, and computer buses, an acknowledgment (ACK) is a signal that is passed between communicating processes, computers, or devices to signify acknowledgment, or receipt of message, as part of a communicatio ...
is a liquid used as a heat-transfer medium and a
desiccant A desiccant is a hygroscopic substance that is used to induce or sustain a state of dryness (desiccation) in its vicinity; it is the opposite of a humectant. Commonly encountered pre-packaged desiccants are solids that absorb water. Desiccant ...
for producing air-free technique, dry and air-free solvents. It can also be used in reactive distillation. The ternary alloy of 12% Na, 47% K and 41% Cs has the lowest melting point of −78°C of any metallic compound. Metallic potassium is used in several types of magnetometers.


Precautions

Potassium metal can react violently with water producing
potassium hydroxide Potassium hydroxide is an inorganic compound with the formula K OH, and is commonly called caustic potash. Along with sodium hydroxide (NaOH), KOH is a prototypical strong base. It has many industrial and niche applications, most of which exp ...
(KOH) and
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
gas. : This reaction is exothermic and releases sufficient heat to ignite the resulting hydrogen in the presence of oxygen. Finely powdered potassium ignites in air at room temperature. The bulk metal ignites in air if heated. Because its density is 0.89g/cm3, burning potassium floats in water that exposes it to atmospheric oxygen. Many common fire extinguishing agents, including water, either are ineffective or make a potassium fire worse. Nitrogen,
argon Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abu ...
, sodium chloride (table salt), sodium carbonate (soda ash), and silicon dioxide (sand) are effective if they are dry. Some Fire extinguisher, Class D dry powder extinguishers designed for metal fires are also effective. These agents deprive the fire of oxygen and cool the potassium metal. During storage, potassium forms peroxides and superoxides. These peroxides may react violently with organic compounds such as oils. Both peroxides and superoxides may react explosively with metallic potassium. Because potassium reacts with water vapor in the air, it is usually stored under anhydrous mineral oil or kerosene. Unlike lithium and sodium, however, potassium should not be stored under oil for longer than six months, unless in an inert (oxygen free) atmosphere, or under vacuum. After prolonged storage in air dangerous shock-sensitive peroxides can form on the metal and under the lid of the container, and can detonate upon opening. Ingestion of large amounts of potassium compounds can lead to hyperkalemia, strongly influencing the cardiovascular system. Potassium chloride is used in the United States for lethal injection executions.


See also


References


Bibliography

* * * *
National Nutrient Database
at USDA Website


External links

* {{Authority control Potassium, Chemical elements Alkali metals Desiccants Dietary minerals Reducing agents Chemical elements with body-centered cubic structure Articles containing video clips