Potassium is a chemical element with symbol K (from Neo-Latin kalium)
and atomic number 19. 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 the alkali metals have a
single valence electron in the outer electron shell, which is easily
removed to create an ion with a positive charge – a cation, which
combines with anions to form salts.
Potassium in nature occurs only in
ionic salts. Elemental potassium is a soft silvery-white alkali metal
that oxidizes rapidly in air and 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), and is part of many
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, and was proven in 1807
using electrolysis. Naturally occurring potassium is composed of three
isotopes, of which 40K is radioactive. Traces of 40K are found in all
potassium, and it is the most common radioisotope in the human body.
Potassium ions are necessary for the function of all living cells. The
transfer of potassium ions through nerve cell membranes is necessary
for normal nerve transmission; potassium deficiency and excess can
each result in numerous abnormalities, including an abnormal heart
rhythm and various electrocardiographic (ECG) abnormalities. Fresh
fruits and vegetables are good dietary sources of potassium. The body
responds to the influx of dietary potassium, which raises serum
potassium levels, with a shift of potassium from outside to inside
cells and an increase in potassium excretion by the kidneys.
Most industrial applications of potassium exploit the high solubility
in 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.
3 Cosmic formation and distribution
7 Biological role
7.1 Biochemical function
7.2.1 Plasma levels
7.2.2 Control mechanisms
7.2.3 Renal filtration, reabsorption, and excretion
8.1 Dietary recommendations
8.2 Food sources
8.3 Deficient intake
8.5 Detection by taste buds
9 Commercial production
9.2 Chemical extraction
10 Commercial uses
10.2 Food additives
10.3.1 Niche uses
10.3.2 Laboratory uses
12 See also
15 External links
The English name for the element potassium comes from the word
"potash", 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.
The symbol "K" stems from kali, itself from the root word alkali,
which in turn comes from Arabic: القَلْيَه al-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. In 1807, Humphry Davy
produced the element via electrolysis: in 1809, Ludwig Wilhelm Gilbert
proposed the name Kalium for Davy's "potassium". In 1814, the
Swedish chemist Berzelius advocated the name kalium for potassium,
with the chemical symbol "K".
The English and French speaking countries adopted Davy and
Gay-Lussac/Thénard's name Potassium, while the Germanic countries
adopted Gilbert/Klaproth's name Kalium. The "
Gold Book" of the
International Union of Physical and Applied Chemistry has designated
the official chemical symbol as K.
The flame test of potassium.
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. In a flame
test, potassium and its compounds emit a lilac color with a peak
emission wavelength of 766.5 nanometers.
Neutral potassium atoms have 19 electrons, one more than the 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).
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).
Potassium therefore does not
form compounds with the oxidation state of +2 or higher.
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
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. 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. 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. For example,
the preparation of magnesium by this method employs potassium as the
2 + 2 K → Mg + 2 KCl
Structure of solid potassium superoxide (KO
The only common oxidation state for potassium is +1.
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.
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);
they contain three different oxygen-based ions: oxide (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.
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 merely one liter of water.
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
n]+ where n = 6 and 7. 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.
Main article: Isotopes of potassium
There are 24 known isotopes of potassium, three of which occur
naturally: 39K (93.3%), 40K (0.0117%), and 41K (6.7%). Naturally
occurring 40K has a half-life of 1.250×109 years. It decays to stable
40Ar by electron capture or positron emission (11.2%) or to stable
40Ca by beta decay (88.8%). The decay of 40K to 40Ar 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
(40Ar) was quantitatively retained. Minerals are dated by measurement
of the concentration of potassium and the amount of radiogenic 40Ar
that has accumulated. The minerals 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. 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.
40K occurs in natural potassium (and thus in some commercial salt
substitutes) in sufficient quantity that large bags of those
substitutes can be used as a radioactive source for classroom
demonstrations. 40K is the radioisotope with the largest abundance in
the body. In healthy animals and people, 40K represents the largest
source of radioactivity, greater even than 14C. In a human body of
70 kg mass, about 4,400 nuclei of 40K decay per second. The
activity of natural potassium is 31 Bq/g.
Cosmic formation and distribution
Potassium in feldspar
Potassium is formed in supernovas by nucleosynthesis from lighter
Potassium is principally created in Type II supernovas via the
explosive oxygen-burning process. 40K is also formed in s-process
nucleosynthesis and the neon burning process.
Potassium makes up about 2.6% of the weight of the earth's crust and
is the seventh most abundant element in the crust. It is the 17th
most abundant element by weight in the earth, and 20th most abundant
element in the solar system. The potassium concentration in seawater
is 0.39 g/L (0.039 wt/v%), about one twenty-seventh the
concentration of sodium.
Main article: 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
Georg Ernst Stahl obtained
experimental evidence that led him to suggest the fundamental
difference of sodium and potassium salts in 1702, and Henri Louis
Duhamel du Monceau was able to prove this difference in 1736. The
exact chemical composition of potassium and sodium compounds, and the
status as chemical element of potassium and sodium, was not known
then, and thus
Antoine Lavoisier did not include the alkali in his
list of chemical elements in 1789. For a long time the only
significant applications for potash were the production of glass,
bleach, soap and gunpowder as potassium nitrate.
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. The discovery by
Justus Liebig in
1840 that potassium is a necessary element for plants and that most
types of soil lack potassium caused a steep rise in demand for
potassium salts. Wood-ash from fir trees was initially used as a
potassium salt source for fertilizer, but, with the discovery in 1868
of mineral deposits containing potassium chloride near Staßfurt,
Germany, the production of potassium-containing fertilizers began at
an industrial scale. Other potash deposits were
discovered, and by the 1960s
Canada became the dominant
Pieces of potassium metal
Potassium metal was first isolated in 1807 in England 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.
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. Although the
production of potassium and sodium metal should have shown that both
are elements, it took some time before this view was universally
Elemental potassium does not occur in nature because of its high
reactivity. It reacts violently with water (see section Precautions
below) and also reacts with oxygen.
feldspar) is a common rock-forming mineral.
Granite for example
contains 5% potassium, which is well above the average in the Earth's
Sylvite (KCl), carnallite (KCl·MgCl
2O)), kainite (MgSO
2O) and langbeinite (MgSO
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. 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
Potassium in biology
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. 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). Potassium
ions are present in a wide variety of proteins and enzymes.
Potassium levels influence multiple physiological processes,
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.
hormone secretion and action
systemic blood pressure control
glucose and insulin metabolism
renal concentrating ability
fluid and electrolyte balance
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
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, and some cardiac, kidney, and lung
diseases progress more rapidly if serum potassium levels are not
maintained within the normal range.
An average meal of 40-50 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
Hypokalemia, a deficiency of potassium in the plasma, can be fatal if
severe. Common causes are increased gastrintestinal loss (vomiting,
diarrhea), and increased renal loss (diuresis). Deficiency
symptoms include muscle weakness, paralytic ileus, ECG abnormalities,
decreased reflex response; and in severe cases, respiratory paralysis,
alkalosis, and cardiac arrhythmia.
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";[citation
needed] and the first two, the "reactive potassium homeostasis
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
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
The action of the sodium-potassium pump is an example of primary
active transport. The two carrier proteins embedded in the cell
membrane on the left are using ATP 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.
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. 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.
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. 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.
Sodium pumps in the renal tubules operate to
Potassium must be conserved also, but, because the
amount of potassium in the blood plasma is very small and the pool of
potassium in the cells is about thirty times as large, the situation
is not so critical for potassium. Since potassium is moved
passively in counter flow to sodium in response to an apparent
(but not actual) Donnan equilibrium, the urine can never sink
below the concentration of potassium in serum except sometimes by
actively excreting water at the end of the processing.
excreted twice and reabsorbed three times before the urine reaches the
collecting tubules. At that point, urine usually has about the
same potassium concentration as plasma. At the end of the processing,
potassium is secreted one more time if the serum levels are too
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. If potassium is still
withheld, the concentration continues to fall until a severe
deficiency causes eventual death.
The potassium moves passively through pores in the cell membrane. When
ions move through pumps there is a gate in the pumps on either side of
the cell membrane and only one gate can be open at once. As a result,
approximately 100 ions are forced through per second. Pores have only
one gate, and there only one kind of ion can stream through, at 10
million to 100 million ions per second. The pores require calcium
to open although it is thought that the calcium works in reverse
by blocking at least one of the pores. Carbonyl groups inside the
pore on the amino acids mimic the water hydration that takes place in
water solution by the nature of the electrostatic charges on four
carbonyl groups inside the pore.
The U.S. Institute of Medicine (IOM) 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. The current AI for potassium
for women and men ages 14 and up is 4700 mg. AI for pregnancy
equals 4700 mg/day. AI for lactation equals 5100 mg/day. For
infants 0–6 months 400 mg, 6–12 months 700 mg, 1–13
years increasing from 3000 to 4500 mg/day. As for safety, the IOM also
sets Tolerable upper intake levels (ULs) for vitamins and minerals,
but for potassium the evidence was insufficient, so no UL
Most Americans consume only half that amount per day.
Likewise, in the European Union, in particular in
Germany and Italy,
insufficient potassium intake is somewhat common. However, the
National Health Service
National Health Service recommends a lower intake, saying that
adults need 3,500 mg per day and that excess amounts may cause
health problems such as stomach pain and diarrhoea.
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.
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
Diets low in potassium can lead to hypertension and hypokalemia.
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. 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
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
A meta-analysis concluded that a 1640 mg increase in the daily
intake of potassium was associated with a 21% lower risk of
Potassium chloride and potassium bicarbonate may be useful
to control mild hypertension.
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
Sylvite from New Mexico
Potassium salts such as carnallite, langbeinite, polyhalite, and
sylvite form extensive evaporite deposits in ancient lake bottoms and
seabeds, 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. 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 is the
Potash Corporation of Saskatchewan. The water of the
Dead Sea is
Jordan as a source of potash, while the
concentration in normal oceans is too low for commercial production at
Monte Kali, a potash mining and beneficiation waste heap in Hesse,
Germany, consisting mostly of sodium chloride.
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.
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.
Na + KCl → NaCl + K
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
Potassium sulfate/magnesium sulfate fertilizer
Potassium ions are an essential component of plant nutrition and are
found in most soil types. They are used as a fertilizer in
agriculture, horticulture, and hydroponic culture in the form of
chloride (KCl), sulfate (K
4), or nitrate (KNO
3). Agricultural fertilizers consume 95% of global potassium chemical
production, and about 90% of this potassium is supplied as KCl. The
potassium content of most plants range from 0.5% to 2% of the
harvested weight of crops, conventionally expressed as amount of K
2O. 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
2O) and langbeinite (MgSO
4). Only a very few fertilizers contain potassium nitrate. In
2005, about 93% of world potassium production was consumed by the
Potassium sodium tartrate (KNaC
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
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.
Major potassium chemicals are potassium hydroxide, potassium
carbonate, potassium sulfate, and potassium chloride. Megatons of
these compounds are produced annually.
Potassium hydroxide KOH is a strong base, which is used in industry to
neutralize strong and weak acids, to control pH and to manufacture
potassium salts. It is also used to saponify fats and oils, in
industrial cleaners, and in hydrolysis reactions, for example of
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
3 or potash) is used in the manufacture of glass, soap, color TV
tubes, fluorescent lamps, textile dyes and pigments. Potassium
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.
Potassium chromate (K
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, but all these uses are due to the chemistry of
the chromate ion, rather than the potassium ion.
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
2 + 2 CO2 → 2 K
3 + 3 O
Another example is potassium cobaltinitrite, K
6], which is used as artist's pigment under the name of
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.
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. The
ternary alloy of 12% Na, 47% K and 41% Cs has the lowest melting point
of −78 °C of any metallic compound.
Metallic potassium is used in several types of magnetometers.
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.
Potassium metal reacts violently with water producing potassium
hydroxide (KOH) and hydrogen gas.
2 K (s) + 2 H2O (l) → 2 KOH (aq) + H
This reaction is exothermic and releases enough heat to ignite the
resulting hydrogen in the presence of oxygen, possibly explosively
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.
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
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.
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
Potassium chloride is used in the
United States for
lethal injection executions.
View or order collections of articles
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^ Meija, J.; et al. (2016). "Atomic weights of the elements 2013
(IUPAC Technical Report)". Pure and Applied Chemistry. 88 (3):
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Physics (92nd ed.). Boca Raton, FL: CRC Press. p. 4.122.
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CRC Handbook of Chemistry and Physics
CRC Handbook of Chemistry and Physics (86th
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alkalies, and the exhibition of the new substances that constitute
their bases; and on the general nature of alkaline bodies".
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history of the vegetable alkali), Mémoires de l'Académie royale des
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produit de la végétation dans les plantes, occupe une place propre
dans la série des substances primitivement simples du règne
minéral, & il devient nécessaire de lui assigner un nom, qui
convienne mieux à sa nature. La dénomination de Potasche (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 de kali, & de revenir à l'ancienne
dénomination de natron, au lieu de dire alcali minéral, soude
(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
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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
Thus I now propose to substitute for the until now common words of
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kali ; and to return to the old name of natron instead of saying
"mineral alkali", "soda", etc.)
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and Natron-Metalloid, bis zur völligen Aufklärung der chemischen
Natur dieser räthzelhaften Körper bleiben will. Oder vielleicht
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Metalle und Metalloide, und in die letztere Kalium und Natronium zu
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appellations Kali-metalloid and Natron-metalloid which are used by Mr.
Erman [i.e., German physics professor
Paul 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 and
metalloids, and to place Kalium and Natronium in the latter —
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National Nutrient Database at
The Periodic Table of Videos
The Periodic Table of Videos (University of Nottingham)
Potassium (K) at Encyclopædia Britannica
Periodic table (Large cells)
Alkaline earth metal
BNF: cb121440770 (data)