# Potassium

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Potassium,  19K
Potassium pearls (in paraffin oil, ~5 mm each)
Potassium
Pronunciation
Appearancesilvery gray
Standard atomic weight Ar, std(K)39.0983(1) [1]
Potassium in the periodic table
 Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
Na

K

Rb
argonpotassiumcalcium
19
Group group 1: H and alkali metals
Period period 4
Block s-block
Element category   Alkali metal
Electron configuration [ Ar ] 4s1
Electrons per shell
2, 8, 8, 1
Physical properties
Phase at  solid
Melting point 336.7  K (63.5 °C,146.3 °F)
Boiling point 1032 K(759 °C,1398 °F)
Density (near r.t.)0.862 g/cm3
when liquid (at m.p.)0.828 g/cm3
Critical point 2223 K, 16 MPa [2]
Heat of fusion 2.33  kJ/mol
Heat of vaporization 76.9 kJ/mol
Molar heat capacity 29.6 J/(mol·K)
Atomic properties
Oxidation states −1, +1 (a strongly basic oxide)
Electronegativity Pauling scale: 0.82
Ionization energies
• 1st: 418.8 kJ/mol
• 2nd: 3052 kJ/mol
• 3rd: 4420 kJ/mol
• (more)
Van der Waals radius 275 pm
Spectral lines of potassium
Other properties
Natural occurrence primordial
Crystal structure body-centered cubic (bcc)
Speed of sound thin rod2000 m/s(at 20 °C)
Thermal expansion 83.3 µm/(m·K)(at 25 °C)
Thermal conductivity 102.5 W/(m·K)
Electrical resistivity 72 nΩ·m(at 20 °C)
Magnetic ordering paramagnetic [3]
Magnetic susceptibility +20.8·10−6 cm3/mol(298 K) [4]
Young's modulus 3.53 GPa
Shear modulus 1.3 GPa
Bulk modulus 3.1 GPa
Mohs hardness 0.4
Brinell hardness 0.363 MPa
CAS Number 7440-09-7
History
Discovery and first isolation Humphry Davy (1807)
Main isotopes of potassium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
39K93.258% stable
40K 0.012%1.248×109 y β 40Ca
ε 40Ar
β+ 40Ar
41K6.730%stable
| references

Potassium is a chemical element with the symbol K (from Neo-Latin kalium ) and atomic number  19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. [5] Potassium metal reacts rapidly with atmospheric oxygen to form flaky white potassium peroxide in only seconds of exposure. It was first isolated from potash, the ashes of plants, from which its name derives. In the periodic table, potassium is one of the alkali metals, all of which have a single valence electron in the outer electron shell, that is easily removed to create an ion with a positive charge – a cation, that combines with anions to form salts. Potassium in nature occurs only in ionic salts. Elemental potassium reacts vigorously with water, generating sufficient heat to ignite hydrogen emitted in the reaction, and burning with a lilac-colored flame. It is found dissolved in sea water (which is 0.04% potassium by weight [6] [7] ), and occurs in many minerals such as orthoclase, a common constituent of granites and other igneous rocks.

A chemical element is a species of atom having the same number of protons in their atomic nuclei. For example, the atomic number of oxygen is 8, so the element oxygen consists of all atoms which have 8 protons.

In chemistry, a symbol is an abbreviation for a chemical element. Symbols for chemical elements normally consist of one or two letters from the Latin alphabet and are written with the first letter capitalised.

New Latin was a revival in the use of Latin in original, scholarly, and scientific works between c. 1375 and c. 1900. Modern scholarly and technical nomenclature, such as in zoological and botanical taxonomy and international scientific vocabulary, draws extensively from New Latin vocabulary. In such use, New Latin is subject to new word formation. As a language for full expression in prose or poetry, however, it is often distinguished from its successor, Contemporary Latin.

## Contents

Potassium is chemically very similar to sodium, the previous element in group 1 of the periodic table. They have a similar first ionization energy, which allows for each atom to give up its sole outer electron. That they are different elements that combine with the same anions to make similar salts was suspected in 1702, [8] and was proven in 1807 using electrolysis. Naturally occurring potassium is composed of three isotopes, of which 40
K
K
are found in all potassium, and it is the most common radioisotope in the human body.

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, because it has a single electron in its outer shell, which it readily donates, creating a positively charged ion—the Na+ cation. Its only stable isotope is 23Na. The free metal does not occur in nature, and must be prepared from compounds. Sodium is the sixth most abundant element in the Earth's crust and exists in numerous minerals such as feldspars, sodalite, and rock salt (NaCl). Many salts of sodium are highly water-soluble: sodium ions have been leached by the action of water from the Earth's minerals over eons, and thus sodium and chlorine are the most common dissolved elements by weight in the oceans.

In physics and chemistry, ionization energy (American English spelling) or ionisation energy (British English spelling), denoted Ei, is the minimum amount of energy required to remove the most loosely bound electron, the valence electron, of an isolated neutral gaseous atom or molecule. It is quantitatively expressed as

In chemistry and manufacturing, electrolysis is a technique that uses a 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 naturally occurring sources such as ores using an electrolytic cell. The voltage that is needed for electrolysis to occur is called the decomposition potential.

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 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.

Electrocardiography is the process of producing an electrocardiogram, a recording – a graph of voltage versus time – of the electrical activity of the heart using electrodes placed on the skin. These electrodes detect the small electrical changes that are a consequence of cardiac muscle depolarization followed by repolarization during each cardiac cycle (heartbeat). Changes in the normal ECG pattern occur in numerous cardiac abnormalities, including cardiac rhythm disturbances, inadequate coronary artery blood flow, and electrolyte disturbances.

In blood, the serum is the fluid and solute component of blood after clotting. It is neither a blood cell, nor a clotting factor; it is the blood plasma not including the fibrinogens. Serum includes all proteins not used in blood clotting and all the electrolytes, antibodies, antigens, hormones, and any exogenous substances.

Most industrial applications of potassium exploit the high solubility in water of potassium compounds, such as potassium soaps. 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. [9]

Solubility is the property of a solid, liquid or gaseous chemical substance called solute to dissolve in a solid, liquid or gaseous solvent. The solubility of a substance fundamentally depends on the physical and chemical properties of the solute and solvent as well as on temperature, pressure and presence of other chemicals of the solution. The extent of the solubility of a substance in a specific solvent is measured as the saturation concentration, where adding more solute does not increase the concentration of the solution and begins to precipitate the excess amount of solute.

Saltwater soap, also called sailors' soap, is a potassium-based soap for use with seawater. Inexpensive common commercial soap will not lather or dissolve in seawater due to high levels of sodium chloride in the water. Similarly, common soap does not work as well as potassium-based soap in hard water where calcium replaces the sodium, making residual insoluble "scum" due to the insolubility of the soap residue. To be an effective cleaning agent, soap must be able to dissolve in water.

Soap is a salt of a fatty acid used in a variety of cleansing and lubricating products. Household uses for soaps include washing, bathing, and other types of housekeeping, where soaps act as surfactants, emulsifying oils to enable them to be carried away by water. In industry, they are used as thickeners, components of some lubricants, and precursors to catalysts.

## Etymology

The English name for the element potassium comes from the word "potash", [10] 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 first isolated the pure element using electrolysis in 1807, he named it potassium, which he derived from the word potash.

Potash includes various mined and manufactured salts that contain potassium in water-soluble form. The name derives from pot ash, which refers to plant ashes soaked in water in a pot, the primary means of manufacturing the product before the industrial era. The word potassium is derived from potash.

Sir Humphry Davy, 1st Baronet was a Cornish chemist and inventor, who is best remembered today for isolating, using electricity, a series of elements for the first time: potassium and sodium in 1807 and calcium, strontium, barium, magnesium and boron the following year, as well as discovering the elemental nature of chlorine and iodine. He also studied the forces involved in these separations, inventing the new field of electrochemistry. In 1799 Davy experimented with nitrous oxide and was astonished at how it made him laugh, so he nicknamed it "laughing gas", and wrote about its potential anaesthetic properties in relieving pain during surgery.

The symbol "K" stems from kali, itself from the root word alkali , which in turn comes from Arabic : القَلْيَهal-qalyah "plant ashes". In 1797, the German chemist Martin Klaproth discovered "potash" in the minerals leucite and lepidolite, and realized that "potash" was not a product of plant growth but actually contained a new element, which he proposed to call kali. [11] In 1807, Humphry Davy produced the element via electrolysis: in 1809, Ludwig Wilhelm Gilbert proposed the name Kalium for Davy's "potassium". [12] In 1814, the Swedish chemist Berzelius advocated the name kalium for potassium, with the chemical symbol "K". [13]

In chemistry, an alkali is a basic, ionic salt of an alkali metal or alkaline earth metal chemical element. An alkali also can be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The adjective alkaline is commonly, and alkalescent less often, used in English as a synonym for basic, especially for bases soluble in water. This broad use of the term is likely to have come about because alkalis were the first bases known to obey the Arrhenius definition of a base, and they are still among the most common bases.

Martin Heinrich Klaproth was a German chemist who discovered uranium (1789), zirconium (1789), and cerium (1803), and named titanium (1795) and tellurium (1798).

Leucite is a rock-forming mineral composed of potassium and aluminium tectosilicate K[AlSi2O6]. Crystals have the form of cubic icositetrahedra but, as first observed by Sir David Brewster in 1821, they are not optically isotropic, and are therefore pseudo-cubic. Goniometric measurements made by Gerhard vom Rath in 1873 led him to refer the crystals to the tetragonal system. Optical investigations have since proved the crystals to be still more complex in character, and to consist of several orthorhombic or monoclinic individuals, which are optically biaxial and repeatedly twinned, giving rise to twin-lamellae and to striations on the faces. When the crystals are raised to a temperature of about 500 °C they become optically isotropic and the twin-lamellae and striations disappear, although they reappear when the crystals are cooled again. This pseudo-cubic character of leucite is very similar to that of the mineral boracite.

The English and French speaking countries adopted Davy and Gay-Lussac/Thénard's name Potassium, while the Germanic countries adopted Gilbert/Klaproth's name Kalium. [14] The "Gold Book" of the International Union of Pure and Applied Chemistry has designated the official chemical symbol as K. [15]

## Properties

### Physical

Potassium is the second least dense metal after lithium. It is a soft solid with a low melting point, 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. [16] In a flame test, potassium and its compounds emit a lilac color with a peak emission wavelength of 766.5 nanometers. [17]

### Chemical

Neutral potassium atoms have 19 electrons, one more than the extremely stable configuration of the noble gas argon. Because of this and its low first ionization energy of 418.8 kJ/mol, the potassium atom is much more likely to lose the last electron and acquire a positive charge than to gain one and acquire a negative charge (though negatively charged alkalide K
ions are not impossible). [18] [19] This process requires so little energy that potassium is readily oxidized by atmospheric oxygen. In contrast, the second ionization energy is very high (3052 kJ/mol), because removal of two electrons breaks the stable noble gas electronic configuration (the configuration of the inert argon). [19] Potassium therefore does not form compounds with the oxidation state of +2 or higher. [18]

Potassium is an extremely active metal that reacts violently with oxygen in water and air. With oxygen it forms potassium peroxide, and with water potassium forms potassium hydroxide. The reaction of potassium with water is dangerous because of its violent exothermic character and the production of hydrogen gas. Hydrogen reacts again with atmospheric oxygen, producing water, which reacts with the remaining potassium. This reaction requires only traces of water. Because of this, potassium and the liquid sodium-potassium (NaK) alloy are potent desiccants that can be used to dry solvents prior to distillation. [20]

Because of the sensitivity of potassium to water and air, reactions with other elements are possible only in an inert atmosphere such as argon gas using air-free techniques. Potassium does not react with most hydrocarbons such as mineral oil or kerosene. [21] It readily dissolves in liquid ammonia, 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. In a pure solution, potassium slowly reacts with ammonia to form KNH
2
, but this reaction is accelerated by minute amounts of transition metal salts. [22] Because it can reduce the salts to the metal, potassium is often used as the reductant in the preparation of finely divided metals from their salts by the Rieke method. [23] For example, the preparation of magnesium by this method employs potassium as the reductant:

+ 2 K → Mg + 2 KCl

### Compounds

The only common oxidation state for potassium is +1. Potassium metal is a powerful reducing agent that is easily oxidized to the monopositive cation, K+
. Once oxidized, it is very stable and difficult to reduce back to the metal. [18]

Potassium oxidizes faster than most metals and often forms oxides containing oxygen-oxygen bonds, as do all alkali metals except lithium. There are three possible oxides of potassium: potassium oxide (K2O), potassium peroxide (K2O2), and potassium superoxide (KO2); [24] they contain three different oxygen-based ions: oxide (O2−
), peroxide (O2−
2
), and superoxide (O
2
). The latter two species, especially the superoxide, are rare and are formed only in reaction of very electropositive metals (Na, K, Rb, Cs, etc.) with oxygen; these species contain oxygen-oxygen bonds. [22] All potassium-oxygen binary compounds are known to react with water violently, forming potassium hydroxide.

Potassium hydroxide (KOH) is a very strong alkali, and up to 1.21  kg of it can dissolve in a single liter of water. [25] [26] KOH reacts readily with carbon dioxide to produce potassium carbonate, and is used to remove traces of the gas from air.

In general, potassium compounds are highly ionic and, owing to the high hydration energy of the K+
ion, have excellent water solubility. The main species in water solution are the aquated complexes [K(H
2
O)
n
]+
where n = 6 and 7. [27] The potassium ion is colorless in water and is very difficult to precipitate; possible precipitation methods include reactions with sodium tetraphenylborate, hexachloroplatinic acid, and sodium cobaltinitrite into potassium tetraphenylborate, potassium hexachloroplatinate, and potassium cobaltinitrite. [21]

### Isotopes

There are 25 known isotopes of potassium, three of which occur naturally: 39
K
(93.3%), 40
K
(0.0117%), and 41
K
(6.7%). Naturally occurring has a half-life of 1.250×109 years. It decays to stable by electron capture or positron emission (11.2%) or to stable by beta decay (88.8%). [28] The decay of 40
K
to 40
Ar
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 (40
Ar
) was quantitatively retained. Minerals are dated by measurement of the concentration of potassium and the amount of radiogenic 40
Ar
that has accumulated. The minerals best suited for dating include biotite, muscovite, metamorphic hornblende, and volcanic feldspar; whole rock samples from volcanic flows and shallow instrusives can also be dated if they are unaltered. [28] [29] Apart from dating, potassium isotopes have been used as tracers in studies of weathering and for nutrient cycling studies because potassium is a macronutrient required for life. [30]

40
K
occurs in natural potassium (and thus in some commercial salt substitutes) in sufficient quantity that large bags of those substitutes can be used as a radioactive source for classroom demonstrations. 40
K
is the radioisotope with the largest abundance in the body. In healthy animals and people, 40
K
represents the largest source of radioactivity, greater even than . In a human body of 70 kg mass, about 4,400 nuclei of 40
K
decay per second. [31] The activity of natural potassium is 31 Bq/g. [32]

## Cosmic formation and distribution

Potassium is formed in supernovae by nucleosynthesis from lighter atoms. Potassium is principally created in Type II supernovae via an explosive oxygen-burning process. [33] 40
K
is also formed in s-process nucleosynthesis and the neon burning process. [34]

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 and is the seventh most abundant element in the crust. [35] The potassium concentration in seawater is 0.39 g/L [6] (0.039 wt/v%), about one twenty-seventh the concentration of sodium. [36] [37]

## 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, it was not understood for most of its history to be a fundamentally different substance from sodium mineral salts. Georg Ernst Stahl obtained experimental evidence that led him to suggest the fundamental difference of sodium and potassium salts in 1702, [8] and Henri Louis Duhamel du Monceau was able to prove this difference in 1736. [38] 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 did not include the alkali in his list of chemical elements in 1789. [39] [40] For a long time the only significant applications for potash were the production of glass, bleach, soap and gunpowder as potassium nitrate. [41] 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 soaps. [9] The discovery by Justus Liebig in 1840 that potassium is a necessary element for plants and that most types of soil lack potassium [42] 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 near Staßfurt, Germany, the production of potassium-containing fertilizers began at an industrial scale. [43] [44] [45] Other potash deposits were discovered, and by the 1960s Canada became the dominant producer. [46] [47]

## Metal

Potassium metal was first isolated in 1807 by Sir Humphry Davy, who derived it from caustic potash (KOH, potassium hydroxide) by electrolysis of molten KOH with the newly discovered voltaic pile. Potassium was the first metal that was isolated by electrolysis. [48] Later in the same year, Davy reported extraction of the metal sodium from a mineral derivative (caustic soda, NaOH, or lye) rather than a plant salt, by a similar technique, demonstrating that the elements, and thus the salts, are different. [39] [40] [49] [50] 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. [40]

## Geology

Elemental potassium does not occur in nature because of its high reactivity. It reacts violently with water (see section Precautions below) [21] and also reacts with oxygen. Orthoclase (potassium feldspar) is a common rock-forming mineral. Granite for example contains 5% potassium, which is well above the average in the Earth's crust. Sylvite (KCl), carnallite (KCl·MgCl
2
·6(H
2
O))
, kainite (MgSO
4
·KCl·3H
2
O)
and langbeinite (MgSO
4
·K
2
SO
4
)
are the minerals found in large evaporite deposits worldwide. The deposits often show layers starting with the least soluble at the bottom and the most soluble on top. [37] Deposits of niter (potassium nitrate) 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. [51]

## Biological role

Potassium is the eighth or ninth most common element by mass (0.2%) in the human body, so that a 60 kg adult contains a total of about 120 g of potassium. [52] The body has about as much potassium as sulfur and chlorine, and only calcium and phosphorus are more abundant (with the exception of the ubiquitous CHON elements). [53] Potassium ions are present in a wide variety of proteins and enzymes. [54]

### Biochemical function

Potassium levels influence multiple physiological processes, including [55] [56] [57]

• resting cellular-membrane potential and the propagation of action potentials in neuronal, muscular, and cardiac tissue. Due to the electrostatic and chemical properties, K+
ions are larger than Na+
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. [58]
• 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 5.0 millimoles (mmol) [or milliequivalents (mEq)] per liter by multiple mechanisms. Levels outside this range are associated with an increasing rate of death from multiple causes, [59] and some cardiac, kidney, [60] and lung diseases progress more rapidly if serum potassium levels are not maintained within the normal range.

An average meal of 40-50 mmol presents the body with more potassium than is present in all plasma (20–25 mmol). 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. [61]

Hypokalemia, a deficiency of potassium in the plasma, can be fatal if severe. Common causes are increased gastrointestinal loss (vomiting, diarrhea), and increased renal loss (diuresis). [62] Deficiency symptoms include muscle weakness, paralytic ileus, ECG abnormalities, decreased reflex response; and in severe cases, respiratory paralysis, alkalosis, and cardiac arrhythmia. [63]

#### 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 system, and 4) an internal or cell membrane transport system. Collectively, the first three are sometimes termed the "external potassium homeostasis system"; [64] 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 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 in the suprachiasmatic nucleus 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 forces. The movement of potassium and sodium through the cell membrane is mediated by the Na+/K+-ATPase pump. [65] This ion pump 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 (which are tetramers) are crucial for hyperpolarization inside neurons 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 species. [66]

#### 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 [150 mmol/L, (4.8 g)], while sodium is the major cation of extracellular fluid [150 mmol/L, (3.345 g)]. In the kidneys, about 180 liters of plasma is filtered through the glomeruli and into the renal tubules per day. [67] This filtering involves about 600 g of sodium and 33 g of potassium. Since only 1–10 g of sodium and 1–4 g 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. [68] Sodium pumps 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 [69] [70] in counter flow to sodium in response to an apparent (but not actual) Donnan equilibrium, [71] 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. [72] 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.[ citation needed ]

With no potassium intake, it is excreted at about 200 mg per day until, in about a week, potassium in the serum declines to a mildly deficient level of 3.0–3.5 mmol/L. [73] If potassium is still withheld, the concentration continues to fall until a severe deficiency causes eventual death. [74]

The potassium moves passively through pores in the cell membrane. When ions move through Ion transporters (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 have only one gate, and there only one kind of ion can stream through, at 10 million to 100 million ions per second. [75] Calcium is required to open the pores, [76] although calcium may work in reverse by blocking at least one of the pores. [77] Carbonyl groups inside the pore on the amino acids mimic the water hydration that takes place in water solution [78] by the nature of the electrostatic charges on four carbonyl groups inside the pore. [79]

## Nutrition

### Dietary recommendations

The U.S. National Academy of Medicine (NAM), on behalf of both the U.S. and Canada, sets Estimated Average Requirements (EARs) and Recommended Dietary Allowances (RDAs), or Adequate Intakes (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 Intakes.

For both males and females under 9 years of age, the AIs for potassium are: 400 mg of potassium for 0-6-month-old infants, 860 mg of potassium for 7-12-month-old infants, 2,000 mg of potassium for 1-3-year-old children, and 2,300 mg of potassium for 4-8-year-old children.

For males 9 years of age and older, the AIs for potassium are: 2,500 mg of potassium for 9-13-year-old males, 3,000 mg of potassium for 14-18-year-old males, and 3,400 mg for males that are 19 years of age and older.

For females 9 years of age and older, the AIs for potassium are: 2,300 mg of potassium for 9-18-year-old females, and 2,600 mg of potassium for females that are 19 years of age and older.

For pregnant and lactating females, the AIs for potassium are: 2,600 mg of potassium for 14-18-year-old pregnant females, 2,900 mg for pregnant females that are 19 years of age and older; furthermore, 2,500 mg of potassium for 14-18-year-old lactating females, and 2,800 mg for lactating females that are 19 years of age and older. As for safety, the NAM also sets tolerable upper intake levels (ULs) for vitamins and minerals, but for potassium the evidence was insufficient, so no UL was established. [80] [81]

Most Americans consume only half that amount per day. [82]

Likewise, in the European Union, in particular in Germany and Italy, insufficient potassium intake is somewhat common. [83] The British National Health Service recommends a similar intake, saying that adults need 3,500 mg per day and that excess amounts may cause health problems such as stomach pain and diarrhoea. [84]

### Food sources

Potassium is present in all fruits, vegetables, meat and fish. Foods with high potassium concentrations include yam, parsley, dried apricots, milk, chocolate, all nuts (especially almonds and pistachios), potatoes, bamboo shoots, bananas, avocados, coconut water, soybeans, and bran. [85]

The USDA lists tomato paste, orange juice, beet greens, white beans, potatoes, 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. [86]

### Deficient intake

Diets low in potassium can lead to hypertension [87] 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 make liquid supplements unpalatable. [88] Typical doses range from 10 mmol (400 mg), to 20 mmol (800 mg). 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 99 mg of potassium.[ citation needed ]

Since the kidneys are the site of potassium excretion, individuals with impaired kidney function are at risk for hyperkalemia if dietary potassium and supplements are not restricted. The more severe the impairment, the more severe is the restriction necessary to avoid hyperkalemia.[ citation needed ]

A meta-analysis concluded that a 1640 mg increase in the daily intake of potassium was associated with a 21% lower risk of stroke. [89] Potassium chloride and potassium bicarbonate may be useful to control mild hypertension. [90] In 2016, potassium was the 33rd most prescribed medication in the United States with more than 22 million prescriptions. [91]

### 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. [88] [92]

## Commercial production

### Mining

Potassium salts such as carnallite, langbeinite, polyhalite, and sylvite form extensive evaporite deposits in ancient lake bottoms and seabeds, [36] making extraction of potassium salts in these environments commercially viable. The principal source of potassium – potash – is mined in Canada, Russia, Belarus, Kazakhstan, Germany, Israel, United States, Jordan, and other places around the world. [93] [94] [95] 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 1,000 meters (3,300 feet) 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. [96] 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. [94] [95]

### 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 at different temperatures. 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 after processing. The mineral industry refers to potassium chloride either as potash, muriate of potash, or simply MOP. [37]

Pure potassium metal can be isolated by electrolysis of its 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 in a chemical equilibrium reaction became the dominant method in the 1950s.

The production of 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. [37] [97]

Na + KCl → NaCl + K                     (Thermal method)
2 KF + CaC
2
→ 2 K + CaF
2
+ 2 C    (Griesheimer process)

Reagent-grade potassium metal costs about $10.00/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, a pressure-sensitive explosive that detonates when scratched. The resulting explosion often starts a fire difficult to extinguish. [98] [99]

## Cation identification

Potassium ions can be identified using Sodium cobaltinitrite in the presence of acetic acid.

3K+ + Na3[Co(NO2)6] → K3[Co(NO2)6] + 3Na+

K3[Co(NO2)6] (Potassium cobaltinitrite) is a yellow crystalline precipitate. This reaction cannot be done in basic solution as Co(OH)3 would precipitate instead. It cannot be done in the presence of a mineral acid either as H3[Co(NO2)6] would be formed. Another method of identifying K+ is to treat a potassium salt with Sodium tetraphenylborate.

3K+ + Na[BPh4] → K[BPh4] + 3Na+

## Commercial uses

### Fertilizer

Potassium ions are an essential component of plant nutrition and are found in most soil types. [9] They are used as a fertilizer in agriculture, horticulture, and hydroponic culture in the form of chloride (KCl), sulfate (K
2
SO
4
), or nitrate (KNO
3
), representing the 'K' in 'NPK'. Agricultural fertilizers consume 95% of global potassium chemical production, and about 90% of this potassium is supplied as KCl. [9] The potassium content of most plants ranges from 0.5% to 2% of the harvested weight of crops, conventionally expressed as amount of K
2
O
. Modern high-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 (MgSO
4
·KCl·3H
2
O
) and langbeinite (MgSO
4
·K
2
SO
4
). Only a very few fertilizers contain potassium nitrate. [100] In 2005, about 93% of world potassium production was consumed by the fertilizer industry. [95] Furthermore, potassium can play a key role in nutrient cycling by controlling litter composition. [101]

### Medical use

Potassium, in the form of potassium chloride is used as a medication to treat and prevent low blood potassium. [102] Low blood potassium may occur due to vomiting, diarrhea, or certain medications. [103] It is given by slow injection into a vein or by mouth. [104]

Potassium sodium tartrate (KNaC
4
H
4
O
6
, Rochelle salt) is the main constituent of baking powder; it is also used in the silvering of mirrors. Potassium bromate (KBrO
3
) is a strong oxidizer (E924), used to improve dough strength and rise height. Potassium bisulfite (KHSO
3
) is used as a food preservative, for example in wine and beer-making (but not in meats). It is also used to bleach textiles and straw, and in the tanning of leathers. [105] [106]

### Industrial

Major potassium chemicals are potassium hydroxide, potassium carbonate, potassium sulfate, and potassium chloride. Megatons of these compounds are produced annually. [107]

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 salts. It is also used to saponify fats and oils, in industrial cleaners, and in hydrolysis reactions, for example of esters. [108] [109]

Potassium nitrate (KNO
3
) or saltpeter is obtained from natural sources such as guano and evaporites or manufactured via the Haber process; it is the oxidant in gunpowder (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 complexes. Its applications include gold mining, electroplating, and electroforming of these metals; it is also used in organic synthesis to make nitriles. Potassium carbonate (K
2
CO
3
or potash) is used in the manufacture of glass, soap, color TV tubes, fluorescent lamps, textile dyes and pigments. [110] Potassium permanganate (KMnO
4
) is an oxidizing, bleaching and purification substance and is used for production of saccharin. Potassium chlorate (KClO
3
) is added to matches and explosives. Potassium bromide (KBr) was formerly used as a sedative and in photography. [9]

Potassium chromate (K
2
CrO
4
) is used in inks, dyes, stains (bright yellowish-red color); in explosives and fireworks; in the tanning of leather, in fly paper and safety matches, [111] but all these uses are due to the chemistry of the chromate ion, rather than the potassium ion. [112]

#### Niche uses

There are thousands of uses of various potassium compounds. One example is potassium superoxide, KO
2
, an orange solid that acts as a portable source of oxygen and a carbon dioxide absorber. It is widely used in respiration systems in mines, submarines and spacecraft as it takes less volume than the gaseous oxygen. [113] [114]

4 KO
2
+ 2 CO
2
→ 2 K
2
CO
3
+ 3 O
2

Another example is potassium cobaltinitrite, K
3
[Co(NO
2
)
6
]
, which is used as artist's pigment under the name of Aureolin or Cobalt Yellow. [115]

The stable isotopes of potassium can be laser cooled and used to probe fundamental and technological problems in quantum physics. The two bosonic isotopes possess convenient Feshbach resonances to enable studies requiring tunable interactions, while 40K is one of only two stable fermions amongst the alkali metals. [116]

#### Laboratory uses

An alloy of sodium and potassium, NaK is a liquid used as a heat-transfer medium and a desiccant for producing dry and air-free solvents. It can also be used in reactive distillation. [117] The ternary alloy of 12% Na, 47% K and 41% Cs has the lowest melting point of −78 °C of any metallic compound. [16]

Metallic potassium is used in several types of magnetometers. [118]

## Precautions

Potassium
Hazards
GHS pictograms
GHS signal word Danger
H260, H314
P223, P231+232, P280, P305+351+338, P370+378, P422 [119]
NFPA 704

Potassium metal reacts violently with water producing potassium hydroxide (KOH) and hydrogen gas.

2 K (s) + 2 (l) → 2 KOH (aq) + H
2
↑ (g)

This reaction is exothermic and releases enough heat to ignite the resulting hydrogen in the presence of oxygen. Potassium tends to explode in contact with water and without the oxygen presence. It is called coulombic explosion, possibly splashing onlookers with potassium hydroxide, which is a strong alkali that destroys living tissue and causes skin burns. Finely grated potassium ignites in air at room temperature. The bulk metal ignites in air if heated. Because its density is 0.89 g/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, sodium chloride (table salt), sodium carbonate (soda ash), and silicon dioxide (sand) are effective if they are dry. Some Class D dry powder extinguishers designed for metal fires are also effective. These agents deprive the fire of oxygen and cool the potassium metal. [120]

Potassium reacts violently with halogens and detonates in the presence of bromine. It also reacts explosively with sulfuric acid. During combustion, 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. [121]

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. [122]

Because of the highly reactive nature of potassium metal, it must be handled with great care, with full skin and eye protection and preferably an explosion-resistant barrier between the user and the metal. Ingestion of large amounts of potassium compounds can lead to hyperkalemia, strongly influencing the cardiovascular system. [123] [124] Potassium chloride is used in the United States for lethal injection executions. [123]

## Related Research Articles

The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). Together with hydrogen they comprise group 1, which lies in the s-block of the periodic table. All alkali metals have their outermost electron in an s-orbital: this shared electron configuration results in their having very similar characteristic properties. Indeed, the alkali metals provide the best example of group trends in properties in the periodic table, with elements exhibiting well-characterised homologous behaviour. This family of elements is also known as the lithium family after its leading element.

Hydroxide is a diatomic anion with chemical formula OH. It consists of an oxygen and hydrogen atom held together by a covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, a ligand, a nucleophile, and a catalyst. The hydroxide ion forms salts, some of which dissociate in aqueous solution, liberating solvated hydroxide ions. Sodium hydroxide is a multi-million-ton per annum commodity chemical. A hydroxide attached to a strongly electropositive center may itself ionize, liberating a hydrogen cation (H+), making the parent compound an acid.

Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray solid which bears a close physical resemblance to the other five elements in the second column of the periodic table: all group 2 elements have the same electron configuration in the outer electron shell and a similar crystal structure.

Rubidium is a chemical element with the symbol Rb and atomic number 37. Rubidium is a very soft, silvery-white metal in the alkali metal group. Rubidium metal shares similarities to potassium metal and caesium metal in physical appearance, softness and conductivity. Rubidium cannot be stored under atmospheric oxygen, as a highly exothermic reaction will ensue, sometimes even resulting in the metal catching fire.

In chemistry, a salt is a solid chemical compound consisting of an ionic assembly of cations and anions. Salts are composed of related numbers of cations and anions so that the product is electrically neutral. These component ions can be inorganic, such as chloride (Cl), or organic, such as acetate ; and can be monatomic, such as fluoride (F), or polyatomic, such as sulfate.

An alum is a type of chemical compound, usually a hydrated double sulfate salt of aluminium with the general formula XAl(SO
4
)
2
·12H
2
O
, where X is a monovalent cation such as potassium or ammonium. By itself, "alum" often refers to potassium alum, with the formula KAl(SO
4
)
2
·12H
2
O
. Other alums are named after the monovalent ion, such as sodium alum and ammonium alum.

The chloride ion is the anion Cl. It is formed when the element chlorine gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride salts such as sodium chloride are often very soluble in water. It is an essential electrolyte located in all body fluids responsible for maintaining acid/base balance, transmitting nerve impulses and regulating fluid in and out of cells. Less frequently, the word chloride may also form part of the "common" name of chemical compounds in which one or more chlorine atoms are covalently bonded. For example, methyl chloride, with the standard name chloromethane is an organic compound with a covalent C−Cl bond in which the chlorine is not an anion.

Sodium chloride, commonly known as salt, is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g/mol respectively, 100 g of NaCl contains 39.34 g Na and 60.66 g Cl. Sodium chloride is the salt most responsible for the salinity of seawater and of the extracellular fluid of many multicellular organisms. In its edible form of table salt, it is commonly used as a condiment and food preservative. Large quantities of sodium chloride are used in many industrial processes, and it is a major source of sodium and chlorine compounds used as feedstocks for further chemical syntheses. A second major application of sodium chloride is de-icing of roadways in sub-freezing weather.

Fluoride is an inorganic, monatomic anion with the chemical formula F
, whose salts are typically white or colorless. Fluoride salts typically have distinctive bitter tastes, and are odorless. Its salts and minerals are important chemical reagents and industrial chemicals, mainly used in the production of hydrogen fluoride for fluorocarbons. Fluoride is classified as a weak base since it only partially associates in solution, but concentrated fluoride is corrosive and can attack the skin.

Potassium chloride 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-like taste. KCl is used as a fertilizer, in medicine, in scientific applications, and in food processing, where it may be known as E number additive E508.

Potassium hydroxide is an inorganic compound with the formula KOH, and is commonly called caustic potash.

An iodide ion is the ion I. Compounds with iodine in formal oxidation state −1 are called iodides. This page is for the iodide ion and its salts, not organoiodine compounds. In everyday life, iodide is most commonly encountered as a component of iodized salt, which many governments mandate. Worldwide, iodine deficiency affects two billion people and is the leading preventable cause of intellectual disability.

Potassium cyanide is a compound with the formula KCN. This colorless crystalline salt, similar in appearance to sugar, is highly soluble in water. Most KCN is used in gold mining, organic synthesis, and electroplating. Smaller applications include jewelry for chemical gilding and buffing.

Sodium sulfate (also known as sodium sulphate or sulfate of soda) is the inorganic compound with formula Na2SO4 as well as several related hydrates. All forms are white solids that are highly soluble in water. With an annual production of 6 million tonnes, the decahydrate is a major commodity chemical product. It is mainly used for the manufacture of detergents and in the kraft process of paper pulping.

Potassium sulfate (in British English potassium sulphate (SOP), also called sulphate of potash, arcanite, or archaically known as potash of sulfur) is the inorganic compound with formula K2SO4. It is a white water-soluble solid. It is commonly used in fertilizers, providing both potassium and a source of sulfur.

Water softening is the removal of calcium, magnesium, and certain other metal cations in hard water. The resulting soft water requires less soap for the same cleaning effort, as soap is not wasted bonding with calcium ions. Soft water also extends the lifetime of plumbing by reducing or eliminating scale build-up in pipes and fittings. Water softening is usually achieved using lime softening or ion-exchange resins but is increasingly being accomplished using nanofiltration or reverse osmosis membranes.

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 pseudohexagonal orthorhombic crystals. The mineral is deliquescent (absorbs moisture from the surrounding air) and specimens must be stored in an airtight container.

Sodium ions (Na+) are necessary in small amounts for some types of plants, but sodium as a nutrient is more generally needed in larger amounts by animals, due to their use of it for generation of nerve impulses and for maintenance of electrolyte balance and fluid balance. In animals, sodium ions are necessary for the aforementioned functions and for heart activity and certain metabolic functions. The health effects of salt reflect what happens when the body has too much or too little sodium. Characteristic concentrations of sodium in model organisms are: 10mM in E. coli, 30mM in budding yeast, 10mM in mammalian cell and 100mM in blood plasma.

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