Potassium is achemical element; it hassymbolK (fromNeo-Latinkalium) andatomic number19. It is a silvery white metal that is soft enough to easily cut with a knife.[10] Potassium metal reacts rapidly with atmosphericoxygen to form flaky whitepotassium peroxide in only seconds of exposure. It was first isolated frompotash, the ashes of plants, from which its name derives. In theperiodic table, potassium is one of thealkali metals, all of which have a singlevalence electron in the outer electron shell, which is easily removed to createan ion with a positive charge (which combines withanions to formsalts). In nature, potassium occurs only in ionic salts. Elemental potassium reacts vigorously with water, generating sufficient heat to ignitehydrogen emitted in the reaction, and burning with alilac-colored flame. It is found dissolved in seawater (which is 0.04% potassium by weight),[11][12] and occurs in manyminerals such asorthoclase, a common constituent ofgranites and otherigneous rocks.[13]
Potassium is chemically very similar tosodium, the previous element ingroup 1 of the periodic table. They have a similar firstionization energy, which allows for each atom to give up its sole outer electron. It was first suggested in 1702 that they were distinct elements that combine with the same anions to make similar salts,[14] which was demonstrated in 1807 when elemental potassium was first isolated viaelectrolysis. Naturally occurring potassium is composed of threeisotopes, of which40 K isradioactive. Traces of40 K are found in natural sources of potassium, and it is the most commonradioisotope 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 variouselectrocardiographic abnormalities. Fresh fruits and vegetables are good dietary sources of potassium. The body responds to the influx of dietary potassium by increasing potassium excretion by the kidneys and sequestering potassium in the liver and muscles to avoid changes inserum potassium levels.
Most industrial applications of potassium exploit the highsolubility of its compounds in water, such assaltwater soap. 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.[15]
Etymology
The English name for the elementpotassium comes from the wordpotash, which refers to an early method of extracting various potassium salts: placing in apot theash of burnt wood or tree leaves, adding water, heating, and evaporating the solution.Humphry Davy named the elementpotassium after isolating the metal itself.[16]
The symbolK stems fromkali, itself from the root wordalkali, which in turn comes fromArabic:القَلْيَهal-qalyah 'plant ashes'. In 1797, the German chemistMartin Klaproth discovered "potash" in the mineralsleucite andlepidolite, and realized that "potash" was not a product of plant growth but actually contained a new element, which he proposed callingkali.[17] In 1807, Humphry Davy produced the element via electrolysis: in 1809,Ludwig Wilhelm Gilbert proposed the nameKalium for Davy's "potassium".[18] In 1814, the Swedish chemistBerzelius advocated the namekalium for potassium, with the chemical symbolK.[19]
Potassiummetal was first isolated in 1807 by Humphry Davy, who derived it by electrolysis of moltencaustic potash (KOH) with the newly discoveredvoltaic pile. Potassium was the first metal that was isolated by electrolysis.[22] Later in the same year, Davy reported extraction of the metalsodium 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.[23][24][25][26] 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.[24]
Properties
Pieces of potassium metal
Potassium is a soft silvery solid that easily cut with a knife.[27] Because of the sensitivity of potassium to water and air,air-free techniques are normally employed for handling the element. It is unreactive toward nitrogen and saturated hydrocarbons such as mineral oil orkerosene. It readily dissolves in liquidammonia, up to 480 g per 1000 g of ammonia at 0°C to form theelectride[K(NH3)6]+e−, which features an electron as ananion.[28]
Compounds
Structure of solid potassium superoxide (KO2)
Reflecting its low firstionization energy of 418.8kJ/mol, potassium is a strong reducing agent, i.e., it readily releases an electron upon contact with other materials. Withgraphite, potassium metal formsgraphite intercalation compounds. One such compound has the formula KC8, a gold colored solid that is described as a K+ salt of negatively charged graphite.[29] Potassium can reduce manysalts to the metal as illustrated by theRieke method for making magnesium powder frommagnesium chloride:[30]
MgCl2 + 2 K → Mg + 2 KCl
Most potassium compounds are ionic. Owing to the high hydration energy of theK+ ion, these salts often exhibit excellent water solubility. The main species in water solution are theaquo complexes[K(H2O)n]+ wheren = 6 and 7.[31] Although typically insoluble in organic solvents, potassium salts dissolve in polar organic solvents in the presence ofcrown ethers andcryptand. These organicligands envelop K+ ions, giving lipophiliccoordination complexes. Similar complexation phenomena are found for some ion-binding antibiotics.[32]
Binary compounds
Potassium forms many binary compounds, i.e., compounds of potassium and one other element. The inventory is so extensive that one gap merits mention: no nitride of potassium is known.Potassium hydride forms directly from the elements:[33]
2 K + H2 → 2 KH
It is a white, pyrophoric solid that finds some use as a base.
Although rarely encountered inanhydrous form, KOH is one of the dominant compounds of potassium from the commercial perspective. It is astrong base and highly corrosive. Illustrative of itshydrophilic character, as much as 1.21kg of KOH can dissolve in a liter of water.[36][37] KOH reacts readily withcarbon dioxide (CO2) to producepotassium carbonate (K2CO3), and in principle could be used to remove traces of the gas from air. Like the closely relatedsodium hydroxide, KOH reacts withfats to producesoaps. Potassium-based soaps are used in soap dispensers because they more soluble in water than sodium soaps.[38]
There are 25 knownisotopes of potassium, three of which occur naturally:39 K (93.3%),40 K (0.0117%), and41 K (6.7%) (by mole fraction). Naturally occurring40 K has ahalf-life of1.250×109 years. It decays to stable40 Ar byelectron capture orpositron emission (11.2%) or to stable40 Ca bybeta decay (88.8%).[46] This decay results in a relatively higher concentration of Argon in the atmosphere.[47]: 40 The decay of40 K to40 Ar is the basis of a common method for dating rocks. The conventionalpotassium–argon 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 radiogenic40 Ar that has accumulated. The minerals best suited for dating includebiotite,muscovite,metamorphichornblende, and volcanicfeldspar;whole rock samples from volcanic flows and shallowinstrusives can also be dated if they are unaltered.[46][48] Apart from dating, potassium isotopes have been used astracers in studies ofweathering and fornutrient cycling studies because potassium is amacronutrient required forlife[49] on Earth.
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 abundancein the human body. In healthy animals and people,40 K represents the largest source of radioactivity, greater even than14 C. In a human body of 70 kg, about 4,400 nuclei of40 K decay per second.[50] The activity of natural potassium is 31Bq/g.[51]
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 ofcalcium salts of relatively low solubility in water. While potash has been used since ancient times, its composition was not understood.Georg Ernst Stahl obtained experimental evidence that led him to suggest the fundamental difference of sodium and potassium salts in 1702,[14] andHenri Louis Duhamel du Monceau was able to prove this difference in 1736.[52] The exact chemical composition of potassium and sodium compounds, and the status as chemical element of potassium and sodium, was not known then, and thusAntoine Lavoisier did not include the alkali in his list of chemical elements in 1789.[23][24] For a long time the only significant applications for potash were the production of glass, bleach, soap andgunpowder as potassium nitrate.[53] 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.[15] The discovery byJustus Liebig in 1840 that potassium is a necessary element for plants and that most types of soil lack potassium[54] 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 containingpotassium chloride nearStaßfurt, Germany, the production of potassium-containing fertilizers began at an industrial scale.[55][56][57] Other potash deposits were discovered, and by the 1960s Canada became the dominant producer.[58][59]
Potassium is the 20th most abundant element in theSolar System and the 17th most abundant element by weight in the Earth. It makes up about 2.6% of the weight of theEarth's crust and is the seventh most abundant element in the crust.[63] The potassium concentration in seawater is 0.39g/L[11] (0.039 wt/v%), about one twenty-seventh the concentration of sodium.[64][65]
Elemental potassium does not occur in nature because of its high reactivity with water[28] and 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·MgCl2·6H2O),kainite (MgSO4·KCl·3H2O), andlangbeinite (MgSO4·K2SO4) are the minerals found in largeevaporite deposits worldwide. The deposits often show layers starting with the least soluble at the bottom and the most soluble on top.[65] 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.[66]
Potassium salts such ascarnallite,langbeinite,polyhalite, andsylvite form extensiveevaporite deposits in ancient lake bottoms andseabeds,[64] making extraction of potassium salts in these environments commercially viable. The principal source of potassium – potash – is mined inCanada,Russia,Belarus,Kazakhstan,Germany,Israel, the U.S.,Jordan, and other places around the world.[67][68][69] The first mined deposits were located near Staßfurt, Germany, but the deposits span fromGreat Britain over Germany into Poland. They are located in theZechstein and were deposited in the Middle to LatePermian. Canada leads the world production of potash; the easiest deposits to mine lie 1,000 meters (3,300 feet) below the surface of the Canadian province ofSaskatchewan.[70] The water of theDead 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.[68][69]
Chemical extraction
Several methods are used to separate potassium salts fromsodium andmagnesium 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 resultingsodium andmagnesium waste is either stored underground or piled up inslag 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.[65]
Potassium metal can be isolated by electrolysis of itshydroxide in a process that has changed little since it was first used by Humphry Davy in 1807.[47]: 40 Although the electrolysis process was developed and used in industrial scale in the 1920s, the thermal method, reacting sodium withpotassium chloride in a chemical equilibrium reaction,
Na + KCl → NaCl + K,
became the dominant method in the 1950s.[47]: 40 The production ofsodium–potassium alloys is accomplished by changing the reaction time and the amount of sodium used in the reaction. The Griesheimer process employing the reaction ofpotassium fluoride withcalcium carbide was also used to produce potassium.[65][71]
Potassium ions are an essential component ofplant nutrition and are found in mostsoil types.[15] They are used as afertilizer inagriculture,horticulture, andhydroponic culture in the form ofchloride (KCl),sulfate (K2SO4), ornitrate (KNO3), representing the 'K'in 'NPK'. Agricultural fertilizers consume 95% of global potassium chemical production, and about 90% of this potassium is supplied as KCl.[15] The potassium content of most plants ranges from 0.5% to 2% of the harvested weight of crops, conventionally expressed as amount ofK2O. 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 mineralskainite (MgSO4·KCl·3H2O) andlangbeinite (MgSO4·K2SO4). Only a very few fertilizers contain potassium nitrate.[74] In 2005, about 93% of world potassium production was consumed by the fertilizer industry.[69] Furthermore, potassium can play a key role in nutrient cycling by controlling litter composition.[75]
Potassium sodium tartrate (KNaC4H4O6,Rochelle salt) is a main constituent of some varieties ofbaking powder; it is also used in thesilvering of mirrors.Potassium bromate (KBrO3) is a strong oxidizer (E924), used to improvedough strength and rise height.Potassium bisulfite (KHSO3) is used as a food preservative, for example inwine andbeer-making (but not in meats). It is also used tobleach textiles and straw, and in the tanning ofleathers.[80][81]
Industrial
Major potassium chemicals are potassium hydroxide, potassium carbonate, potassium sulfate, and potassium chloride. Megatons of these compounds are produced annually.[82]
KOH is a strong base, which is used in industry to neutralize strong and weakacids, to controlpH and to manufacture potassiumsalts. It is also used tosaponify fats andoils, in industrial cleaners, and in hydrolysis reactions, for example ofesters.[83][84]
There are thousands of uses of various potassium compounds. One example ispotassium superoxide,KO2, an orange solid that acts as a portable source of oxygen and a carbon dioxide absorber. It is widely used inrespiration systems in mines, submarines and spacecraft as it takes less volume than the gaseous oxygen.[88][89]
The stable isotopes of potassium can belaser cooled and used to probe fundamental andtechnological problems inquantum physics. The twobosonic isotopes possess convenientFeshbach resonances to enable studies requiring tunable interactions, while40 K is one of only two stablefermions amongst the alkali metals.[91]
Laboratory uses
Analloy of sodium and potassium,NaK is a liquid used as a heat-transfer medium and adesiccant for producingdry and air-free solvents. It can also be used inreactive distillation.[92] The ternary alloy of 12% Na, 47% K and 41% Cs has the lowest melting point of −78°C of any metallic compound.[27]
Potassium is crucial for diverse plant species. It has a vital role in maintaining cell sap and internal root pressure required for plant growth. Potassium increases plant metabolism and uptake of carbon dioxide.[47]: 48
Human physiology
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.[94] The body has about as much potassium as sulfur and chlorine, and only calcium and phosphorus are more abundant (with the exception of the ubiquitousCHON elements).[95] Potassium ions are present in a wide variety of proteins and enzymes.[96] 98% of the potassium in a human body is inside of individual cells.[97]
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 thanNa+ 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.[101]
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
local cortical monoaminergic norepinephrine, serotonin, and dopamine levels, and through them, sleep/wake balance, and spontaneous activity.[102]
Homeostasis
Almost all cells have asodium–potassium pump transporting sodium ions out and potassium ions in, maintaining a balance in a narrow range of concentrations essential to cell function. This internal homeostasis mechanism requires an external homeostasis mechanism to maintain the concentration of potassium ions in plasma in the intercellular space. External homeostasis is primarily provide by the kidneys.[103]
The action of thesodium–potassium pump is an example of primaryactive transport. The two carrier proteins embedded in the cell membrane on the left are usingATP to move sodium out of the cell against the concentration gradient; The two proteins on the right are using secondary active transport to move potassium into the cell. This process results in reconstitution of ATP.
Internal (cellular) homeostasis
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 byosmotic forces. The movement of potassium and sodium through the cell membrane is mediated by theNa⁺/K⁺-ATPase pump.[104] Thision pump usesATP 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 selectivepotassium ion channels (which aretetramers) are crucial forhyperpolarization insideneurons 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 fromprokaryotic species.[105]
Potassium can be sequestered in the liver and muscle. This potassium can be released into the extra-cellular plasma between meals to maintain potassium levels.[103]
Plasma levels
Plasma potassium is normally kept at 3.5 to 5.5 millimoles (mmol) [or milliequivalents (mEq)] per liter by multiple mechanisms.[106] Even narrower ranges are required to reduce mortality for patients withacute myocardial infarction.[107]
An average meal of 40–50mmol presents the body with more potassium than is present in all plasma (20–25mmol). Renal and extrarenal mechanisms external homeostasis mechanisms limit the rise in plasma potassium to less than 10%.[108]
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).[109] Deficiency symptoms include muscle weakness,paralytic ileus, ECG abnormalities, decreased reflex response; and in severe cases, respiratory paralysis,alkalosis, andcardiac arrhythmia.[110]
External (plasma-level) homeostasis
Potassium content in the plasma is tightly controlled by three basic mechanisms:[103]
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).[103]
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 triggervagalafferent signals to the pituitary gland.[103]
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 acircadian oscillator in thesuprachiasmatic nucleus of the brain (central clock), which causes the kidney (peripheral clock) to secrete potassium in this rhythmic circadian fashion.[103]
Renal filtration, reabsorption, and excretion
Potassium ions are reabsorbed from blood plasma entering theglomeruli into therenal tubule of the kidneys. Only a small amount of potassium reaches the distalnephron.[111]
Renal handling of potassium is closely connected to sodium handling. Potassium is the major cation (positive ion) inside animal cells (150mmol/L, 4.8g/L), while sodium is the major cation ofextracellular fluid (150mmol/L, 3.345g/L). In the kidneys, about 180liters of plasma is filtered through theglomeruli and into therenal tubules per day.[112] 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.[113]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[114][115] in counter flow to sodium in response to an apparent (but not actual)Donnan equilibrium,[116] 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.[117]
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.[118] If potassium is still withheld, the concentration continues to fall until a severe deficiency causes eventual death.[119]
The potassium moves passively through pores in the cell membrane. When ions move throughion 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 channels have only one gate, and there only one kind of ion can stream through, at 10 million to 100 million ions per second.[120] Calcium is required to open the pores,[121] although calcium may work in reverse by blocking at least one of the pores.[122] Carbonyl groups inside the pore on the amino acids mimic the water hydration that takes place in water solution[123] by the nature of the electrostatic charges on four carbonyl groups inside the pore.[124]
Nutrition
Dietary recommendations
North America
The U.S.National Academy of Medicine (NAM), on behalf of both the U.S. and Canada, setsDietary Reference Intakes, including Estimated Average Requirements (EARs) and Recommended Dietary Allowances (RDAs), orAdequate Intakes (AIs) for when there is not sufficient information to set EARs and RDAs. For both males and females under 9 years of age, the AIs for potassium are: 400mg of potassium for 0 to 6-month-old infants, 860mg of potassium for 7 to 12-month-old infants, 2,000mg of potassium for 1 to 3-year-old children, and 2,300mg of potassium for 4 to 8-year-old children. For males 9 years of age and older, the AIs for potassium are: 2,500mg of potassium for 9 to 13-year-old males, 3,000mg of potassium for 14 to 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 to 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 to 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 to 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 setstolerable upper intake levels (ULs) for vitamins and minerals, but for potassium the evidence was insufficient, so no UL was established.[125][126]
As of 2004, most Americans adults consume less than 3,000mg.[127]
Europe
Likewise, in the European Union, in particular in Germany, and Italy, insufficient potassium intake is somewhat common.[128] TheNational Health Service in the United Kingdom recommends that "adults (19 to 64 years) need3500 mg per day" and that excess amounts may cause health problems such as stomach pain anddiarrhea.[129]
Treating or preventing hypokalemia, a common electrolyte imbalance observed in 20% of hospital patients requires potassium supplements. There are many causes of hypokalemia, but in a clinical settingdiuretics that block reabsorption of sodium and water, are the most common drug cause.[135]
A variety of prescription and over-the counter supplements are available.[136] Potassium chloride may be dissolved in water, but the salty/bitter taste makes liquid supplements unpalatable.[137][138] Potassium is also available in tablets or capsules, which are formulated to allow potassium to leach slowly out of a matrix.[79] The mechanism of action of potassium involves various types of transporters and channels that facilitate its movement across cell membranes. This process can lead to an increase in the pumping of hydrogen ions. This, in turn, can escalate the production of gastric acid, potentially contributing to the development of gastric ulcers.[139] An FDA ruling in the US requires warning of this issue on any non-prescription potassium pills with more than 99mg of potassium.[140]
Studies of dietary potassium intake show higher intakes are correlated with lower blood pressures.[141] Studies of potassium supplements to mitigate the impact of hypertension, thereby reducing cardiovascular risk, give conflicting conclusions. Some studies report "a modest but significant impact"[142] Others find no effects.Potassium chloride andpotassium bicarbonate may be useful to control mildhypertension.[143] In 2020, potassium was the 33rd most commonly prescribed medication in the U.S., with more than 17million prescriptions.[144][145]
Other uses of potassium supplements include preventing the formation of kidney stones, a condition that can lead to renal complications if left untreated. Potassium has a role in bone health. It contributes to the acid-base equilibrium in the body and helps protect bone tissue. For individuals with type 2 diabetes, potassium supplementation may be necessary: potassium is essential for the secretion of insulin by pancreatic beta cells, which helps regulate glucose levels.[139]
Excessive potassium intake can have adverse effects, such as gastrointestinal discomfort and disturbances in heart rhythm.[139] Potassium chloride tablets are specifically associated with pill esophagitis.[146]
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.[137][147] As a food additive, potassium chloride has a salty taste. People wishing to increase their potassium intake or to decrease their sodium intake, after checking with a health professional that it is safe to do so, can substitute potassium chloride for some or all of the sodium chloride (table salt) used in cooking and at the table.[148]
Potassium metal can react violently with water producing KOH andhydrogen gas.
2 K(s) + 2 H2O(l) → 2 KOH(aq) + H2(g)↑
A reaction of potassium metal with water. Hydrogen is produced, and with potassium vapor, burns with a pink or lilac flame. Strongly alkaline potassium hydroxide is formed in solution.
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,sodium chloride (table salt),sodium carbonate (soda ash), andsilicon dioxide (sand) are effective if they are dry. SomeClass D dry powder extinguishers designed for metal fires are also effective. These agents deprive the fire of oxygen and cool the potassium metal.[150]
During storage, potassium forms peroxides and superoxides. These peroxides may react violently withorganic compounds such as oils. Both peroxides and superoxides may react explosively with metallic potassium.[151]
Because potassium reacts with water vapor in the air, it is usually stored under anhydrous mineral oil or kerosene. Unlike lithium and sodium, 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.[152]
Ingestion of large amounts of potassium compounds, certain drugs, and homeostatic failure, can lead tohyperkalemia, leading to a variety of brady- and tachy-arrhythmias that can be fatal.[153][154][155] Potassium chloride is used in the U.S. forlethal injection executions.[153]
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^Klaproth, M. (1797) "Nouvelles données relatives à l'histoire naturelle de l'alcali végétal" (New data regarding the natural history of the vegetable alkali),Mémoires de l'Académie royale des sciences et belles-lettres (Berlin), pp. 9–13 ;see p. 13.Archived 2020-01-24 at theWayback Machine From p. 13:"Cet alcali ne pouvant donc plus être envisagé comme un produit de la végétation dans les plantes, occupe une place propre dans la série des substances primitivement simples du règne minéral, &I il devient nécessaire de lui assigner un nom, qui convienne mieux à sa nature. La dénomination dePotasche (potasse) que la nouvelle nomenclature françoise a consacrée comme nom de tout le genre, ne sauroit faire fortune auprès des chimistes allemands, qui sentent à quel point la dérivation étymologique en est vicieuse. Elle est prise en effet de ce qu'anciennement on se servoit pour la calcination des lessives concentrées des cendres, de pots de fer (pott en dialecte de la Basse-Saxe) auxquels on a substitué depuis des fours à calciner. Je propose donc ici, de substituer aux mots usités jusqu'ici d'alcali des plantes, alcali végétal, potasse, &c. celui dekali, & de revenir à l'ancienne dénomination denatron, au lieu de dire alcali minéral, soude &c." (This alkali [i.e., potash] — [which] therefore can no longer be viewed as a product of growth in plants — occupies a proper place in the originally simple series of the mineral realm, and it becomes necessary to assign it a name that is better suited to its nature. The name of "potash" (potasse), which the new French nomenclature has bestowed as the name of the entire species [i.e., substance], would not find acceptance among German chemists, who feel to some extent [that] the etymological derivation of it is faulty. Indeed, it is taken from [the vessels] that one formerly used for the roasting of washing powder concentrated from cinders: iron pots (pott in the dialect of Lower Saxony), for which roasting ovens have been substituted since then. Thus I now propose to substitute for the until now common words of "plant alkali", "vegetable alkali", "potash", etc., that ofkali ; and to return to the old name ofnatron instead of saying "mineral alkali", "soda", etc.)
^Davy, Humphry (1809)."Ueber einige neue Erscheinungen chemischer Veränderungen, welche durch die Electricität bewirkt werden; insbesondere über die Zersetzung der feuerbeständigen Alkalien, die Darstellung der neuen Körper, welche ihre Basen ausmachen, und die Natur der Alkalien überhaupt" [On some new phenomena of chemical changes that are achieved by electricity; particularly the decomposition of flame-resistant alkalis [i.e., alkalies that cannot be reduced to their base metals by flames], the preparation of new substances that constitute their [metallic] bases, and the nature of alkalies generally].Annalen der Physik.31 (2):113–175.Bibcode:1809AnP....31..113D.doi:10.1002/andp.18090310202.p. 157: In unserer deutschen Nomenclatur würde ich die NamenKalium undNatronium vorschlagen, wenn man nicht lieber bei den von Herrn Erman gebrauchten und von mehreren angenommenen BenennungenKali-Metalloid andNatron-Metalloid, bis zur völligen Aufklärung der chemischen Natur dieser räthzelhaften Körper bleiben will. Oder vielleicht findet man es noch zweckmässiger fürs Erste zwei Klassen zu machen,Metalle undMetalloide, und in die letztereKalium undNatronium zu setzen. — Gilbert. (In our German nomenclature, I would suggest the namesKalium andNatronium, if one would not rather continue with the appellationsKali-metalloid andNatron-metalloid which are used by Mr. Erman [i.e., German physics professorPaul Erman (1764–1851)] and accepted by several [people], until the complete clarification of the chemical nature of these puzzling substances. Or perhaps one finds it yet more advisable for the present to create two classes,metals andmetalloids, and to placeKalium andNatronium in the latter — Gilbert.)
^Berzelius, J. Jacob (1814)Försök, att, genom användandet af den electrokemiska theorien och de kemiska proportionerna, grundlägga ett rent vettenskapligt system för mineralogien [Attempt, by the use of electrochemical theory and chemical proportions, to found a pure scientific system for mineralogy]. Stockholm, Sweden: A. Gadelius.,p. 87.
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