Potassium nitrate is a
chemical compoundA chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
with the
formulaA chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
KPotassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
NNitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
OOxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
3. It is an ionic salt of potassium ions K
+ and nitrate ions NO
3−.
It occurs as a mineral
niterNiter or nitre is the mineral form of potassium nitrate, KNO3, also known as saltpeter or saltpetre . Historically, the term "niter" – cognate with "natrium", a Latin word for sodium – has been very vaguely defined, and it has been applied to a variety of other minerals and chemical compounds,...
and is a natural solid source of
nitrogenNitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
. Its common names include saltpetre (saltpeter in American English), from medieval
LatinLatin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
sal petræ: "stone salt" or possibly "Salt of
PetraPetra is a historical and archaeological city in the Jordanian governorate of Ma'an that is famous for its rock cut architecture and water conduits system. Established sometime around the 6th century BC as the capital city of the Nabataeans, it is a symbol of Jordan as well as its most visited...
" and
nitrate of potash. The mineral nitratite also named
Chile saltpetre (American
Chile saltpeter) refers not to potassium nitrate but to the natural mineral form of a similar chemical
sodium nitrateSodium nitrate is the chemical compound with the formula NaNO3. This salt, also known as Chile saltpeter or Peru saltpeter to distinguish it from ordinary saltpeter, potassium nitrate, is a white solid which is very soluble in water...
.
Major uses of potassium nitrate are in fertilizers,
food additiveFood additives are substances added to food to preserve flavor or enhance its taste and appearance.Some additives have been used for centuries; for example, preserving food by pickling , salting, as with bacon, preserving sweets or using sulfur dioxide as in some wines...
,
rocket propellantRocket propellant is mass that is stored in some form of propellant tank, prior to being used as the propulsive mass that is ejected from a rocket engine in the form of a fluid jet to produce thrust. A fuel propellant is often burned with an oxidizer propellant to produce large volumes of very hot...
s and fireworks; it is one of the constituents of
gunpowderGunpowder, also known since in the late 19th century as black powder, was the first chemical explosive and the only one known until the mid 1800s. It is a mixture of sulfur, charcoal, and potassium nitrate - with the sulfur and charcoal acting as fuels, while the saltpeter works as an oxidizer...
.
History of production
The earliest known complete purification process for potassium nitrate was outlined in 1270 by the Arab chemist and engineer Hasan al-Rammah of
SyriaSyria , officially the Syrian Arab Republic , is a country in Western Asia, bordering Lebanon and the Mediterranean Sea to the West, Turkey to the north, Iraq to the east, Jordan to the south, and Israel to the southwest....
in his book
al-Furusiyya wa al-Manasib al-Harbiyya ('The Book of
Military Horsemanship is the historical Arabic term for knightly martial exercise during the Middle Ages, during the Crusades and Mamluk period in particular, especially concerned with medieval Islamic martial arts and equestrianism...
and Ingenious War Devices'). In this book al-Rammah describes first the purification of
barud (crude saltpetre mineral) by boiling it with minimal water and using only the hot solution, then the use of
potassium carbonatePotassium carbonate is a white salt, soluble in water , which forms a strongly alkaline solution. It can be made as the product of potassium hydroxide's absorbent reaction with carbon dioxide. It is deliquescent, often appearing a damp or wet solid...
(in the form of
wood ashWood ash is the residue powder left after the combustion of wood. Main producers of wood ash are wood industries and power plants.-Composition:...
es) to remove calcium and magnesium by precipation of their carbonates from this solution, leaving a solution of purified potassium nitrate, which could then be dried. This was used for the manufacture of gunpowder and explosive devices.
Into the 19th century, niter-beds were prepared by mixing
manureManure is organic matter used as organic fertilizer in agriculture. Manures contribute to the fertility of the soil by adding organic matter and nutrients, such as nitrogen, that are trapped by bacteria in the soil...
with either
mortarMortar is a workable paste used to bind construction blocks together and fill the gaps between them. The blocks may be stone, brick, cinder blocks, etc. Mortar becomes hard when it sets, resulting in a rigid aggregate structure. Modern mortars are typically made from a mixture of sand, a binder...
or wood ashes, common earth and organic materials such as
strawStraw is an agricultural by-product, the dry stalks of cereal plants, after the grain and chaff have been removed. Straw makes up about half of the yield of cereal crops such as barley, oats, rice, rye and wheat. It has many uses, including fuel, livestock bedding and fodder, thatching and...
to give porosity to a compost pile typically 1.5×2×5 meters in size. The heap was usually under a cover from the rain, kept moist with
urineUrine is a typically sterile liquid by-product of the body that is secreted by the kidneys through a process called urination and excreted through the urethra. Cellular metabolism generates numerous by-products, many rich in nitrogen, that require elimination from the bloodstream...
, turned often to accelerate the decomposition, then finally
leachedLeaching is the process of extracting minerals from a solid by dissolving them in a liquid, either in nature or through an industrial process. In the chemical processing industry, leaching has a variety of commercial applications, including separation of metal from ore using acid, and sugar from...
with water after approximately one year, to remove the soluble calcium nitrate. Dung-heaps were a particularly common source:
ammoniaAmmonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
from the decomposition of
ureaUrea or carbamide is an organic compound with the chemical formula CO2. The molecule has two —NH2 groups joined by a carbonyl functional group....
and other nitrogenous materials would undergo bacterial oxidation to produce various nitrates, primarily calcium nitrate, which after leaching into water could be converted to potassium nitrate by the addition of
potashPotash is the common name for various mined and manufactured salts that contain potassium in water-soluble form. In some rare cases, potash can be formed with traces of organic materials such as plant remains, and this was the major historical source for it before the industrial era...
from wood ashes.
A variation on this process, using only urine, straw and wood ash, is described by LeConte in 1862. Stale urine is placed in a container of straw and is allowed to "sour" (bacterially ferment) for many months, after which water is used to wash the resulting chemical salts from the straw. The process is completed by filtering the liquid through wood ashes, then air-drying in the sun. The nitrate source in this process is calcium nitrate produced by bacterial action on the nitrogenous
ureaUrea or carbamide is an organic compound with the chemical formula CO2. The molecule has two —NH2 groups joined by a carbonyl functional group....
and ammonia from urine, combined with calcium from urine. This calcium nitrate salt is converted again in the standard way to soluble potassium nitrate, using potassium carbonate from potash.
During this period, the major natural sources of potassium nitrate were the deposits crystallizing from cave walls and the accumulations of bat guano in caves. Traditionally guano was the source used in
LaosLaos Lao: ສາທາລະນະລັດ ປະຊາທິປະໄຕ ປະຊາຊົນລາວ Sathalanalat Paxathipatai Paxaxon Lao, officially the Lao People's Democratic Republic, is a landlocked country in Southeast Asia, bordered by Burma and China to the northwest, Vietnam to the east, Cambodia to the south and Thailand to the west...
for the manufacture of gunpowder for
Bang FaiA Rocket Festival is a merit-making ceremony traditionally practiced by Ethnic Lao people throughout much of northeast Thailand and Laos, by numerous villages and municipalities near the beginning of the rainy season...
rockets.
Potassium nitrates not only supplied the oxidant and much of the energy for gunpowder in the 19th century, but after 1889 small arms and large artillery increasingly began to depend on
corditeCordite is a family of smokeless propellants developed and produced in the United Kingdom from 1889 to replace gunpowder as a military propellant. Like gunpowder, cordite is classified as a low explosive because of its slow burning rates and consequently low brisance...
, a
smokeless powderSmokeless powder is the name given to a number of propellants used in firearms and artillery which produce negligible smoke when fired, unlike the older gunpowder which they replaced...
which required in manufacture large quantities of
nitric acidNitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...
derived from mineral nitrates (either potassium nitrate, or increasingly
sodium nitrateSodium nitrate is the chemical compound with the formula NaNO3. This salt, also known as Chile saltpeter or Peru saltpeter to distinguish it from ordinary saltpeter, potassium nitrate, is a white solid which is very soluble in water...
), and the basic industrial chemical
sulfuric acidSulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
. These propellants, like all nitrated explosives (nitroglycerine,
TNT, etc.) use the energy available when organic nitrates burn or explode and are converted to
nitrogenNitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
gas, a process that releases large amounts of energy.
From 1903 until the
World War IWorld War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...
era, potassium nitrate for black powder and fertilizer was produced on an industrial scale from nitric acid produced via the Birkeland–Eyde process, which used an electric arc to oxidize nitrogen from the air. During World War I the newly industrialized
Haber processThe Haber process, also called the Haber–Bosch process, is the nitrogen fixation reaction of nitrogen gas and hydrogen gas, over an enriched iron or ruthenium catalyst, which is used to industrially produce ammonia....
(1913) was combined with the
Ostwald processThe Ostwald process is a chemical process for producing nitric acid, which was developed by Wilhelm Ostwald . It is a mainstay of the modern chemical industry. Historically and practically it is closely associated with the Haber process, which provides the requisite raw material,...
after 1915, allowing Germany to produce nitric acid for the war after being cut off from its supplies of mineral sodium nitrates from Chile (see nitratite). The Haber process
catalyzesCatalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. A catalyst may participate in multiple chemical transformations....
ammonia production from atmospheric nitrogen, and industrially-produced hydrogen. From the end of World War I until today, practically all organic nitrates have been produced from nitric acid from the oxidation of ammonia in this way. Some sodium nitrate is still mined industrially. Almost all potassium nitrate, now used only as a fine chemical, is produced from basic potassium salts and nitric acid.
Production
Potassium nitrate can be made by combining
ammonium nitrate and
potassium hydroxidePotassium hydroxide is an inorganic compound with the formula KOH, commonly called caustic potash.Along with sodium hydroxide , this colorless solid is a prototypical strong base. It has many industrial and niche applications. Most applications exploit its reactivity toward acids and its corrosive...
.
- NH4NO3 (aq) + KOH (aq) → NH3 (g) + KNO3 (aq) + H2O (l)
An alternative way of producing potassium nitrate without a by-product of ammonia is to combine
ammonium nitrate and
potassium chlorideThe chemical compound potassium chloride is a metal halide salt composed of potassium and chlorine. In its pure state, it is odorless and has a white or colorless vitreous crystal appearance, with a crystal structure that cleaves easily in three directions. Potassium chloride crystals are...
, easily obtained as a sodium-free
salt substituteSalt substitutes are low-sodium table salt alternatives marketed to circumvent the risk of high blood pressure and cardiovascular disease associated with a high intake of sodium chloride while maintaining a similar taste...
.
- NH4NO3 (aq) + KCl (aq) → NH4Cl (aq) + KNO3 (aq)
Potassium nitrate can also be produced by neutralizing nitric acid with
potassium hydroxidePotassium hydroxide is an inorganic compound with the formula KOH, commonly called caustic potash.Along with sodium hydroxide , this colorless solid is a prototypical strong base. It has many industrial and niche applications. Most applications exploit its reactivity toward acids and its corrosive...
. This reaction is highly exothermic.
- KOH (aq) + HNO3 → KNO3 (aq) + H2O (l)
Properties
Potassium nitrate has an orthorhombic crystal structure at room temperature, which transforms to a trigonal system at 129 °C. Upon heating to temperatures above 560 °C, it decomposes into
potassium nitritePotassium nitrite is a salt with chemical formula 2.It is a strong oxidizer and may accelerate the combustion of other materials. Like other nitrite salts such as sodium nitrite, potassium nitrite is toxic if swallowed, and laboratory tests suggest that it may be mutagenic or teratogenic...
, generating oxygen:
- 2 KNO3 → 2 KNO2 + O2
Potassium nitrate is moderately soluble in water, but its solubility increases with temperature (see infobox). The aqueous solution is almost neutral, exhibiting
pHIn chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
6.2 at 14 °C for a 10% solution of commercial powder. It is not very hygroscopic, absorbing about 0.03% water in 80%
relative humidityRelative humidity is a term used to describe the amount of water vapor in a mixture of air and water vapor. It is defined as the partial pressure of water vapor in the air-water mixture, given as a percentage of the saturated vapor pressure under those conditions...
over 50 days. It is insoluble in alcohol and is not poisonous; it can react explosively with reducing agents, but it is not explosive on its own.
Fertilizer
Potassium nitrate is mainly used in
fertilizerFertilizer is any organic or inorganic material of natural or synthetic origin that is added to a soil to supply one or more plant nutrients essential to the growth of plants. A recent assessment found that about 40 to 60% of crop yields are attributable to commercial fertilizer use...
s, as a source of nitrogen and potassium – two of the
macro nutrients'Plant Nutrition is the study of the chemical elements that are necessary for growth. In 1972, E. Epstein defined 2 criteria for an element to be essential for plant growth:# in its absence the plant is unable to complete a normal life cycle or...
for plants. When used by itself, it has an
NPK ratingNPK rating is used to label fertilizer based on the relative content of the chemicals nitrogen, phosphorus, and potassium that are commonly used in fertilizers....
of 13-0-44.
Oxidizer
Potassium nitrate is an efficient oxidizer, producing a lilac-colored flame upon burning due to the presence of potassium. It is one of the three components of black powder, along with powdered charcoal (substantially carbon) and sulfur, both of which act as fuels in this composition. As such it is used in
black powder rocket motorA black powder rocket motor propels a model rocket using black powder. Black powder rocket propellants consist of charcoal, sulphur, and potassium nitrate, and some use dextrin as a binder...
s, but also in combination with other fuels like sugars in "
rocket candyRocket candy is a type of rocket propellant for model rockets made with sugar as a fuel, and containing an oxidizer. The propellant can be divided into three groups of components: the fuel, the oxidizer, and the additive. The fuel is a sugar; sucrose is the most commonly used. The most common...
". It is also used in fireworks such as
smoke bombA smoke bomb is a firework designed to produce smoke upon ignition. Smoke bombs are useful to military units, airsoft games, paintball games, self defense and pranks...
s, made with a mixture of
sucroseSucrose is the organic compound commonly known as table sugar and sometimes called saccharose. A white, odorless, crystalline powder with a sweet taste, it is best known for its role in human nutrition. The molecule is a disaccharide composed of glucose and fructose with the molecular formula...
and potassium nitrate. It is also added to pre-rolled cigarettes to maintain an even burn of the tobacco and is used to ensure complete combustion of
paper cartridgePaper cartridge refers to one of various types of small arms ammunition used before the advent of the metallic cartridge. These cartridges consisted of a paper cylinder or cone containing the bullet, gunpowder, and, in some cases, a primer or a lubricating and anti-fouling agent...
s for cap and ball revolvers.
Food preservation
In the process of
food preservationFood preservation is the process of treating and handling food to stop or slow down spoilage and thus allow for longer storage....
, potassium nitrate has been a common ingredient of salted meat since the
Middle AgesThe Middle Ages is a periodization of European history from the 5th century to the 15th century. The Middle Ages follows the fall of the Western Roman Empire in 476 and precedes the Early Modern Era. It is the middle period of a three-period division of Western history: Classic, Medieval and Modern...
, but its use has been mostly discontinued due to inconsistent results compared to more modern nitrate and nitrite compounds. Even so, saltpetre is still used in some food applications, such as
charcuterieCharcuterie is the branch of cooking devoted to prepared meat products such as bacon, ham, sausage, terrines, galantines, pâtés, and confit, primarily from pork. Charcuterie is part of the garde manger chef's repertoire...
and the
brineBrine is water, saturated or nearly saturated with salt .Brine is used to preserve vegetables, fruit, fish, and meat, in a process known as brining . Brine is also commonly used to age Halloumi and Feta cheeses, or for pickling foodstuffs, as a means of preserving them...
used to make
corned beefCorned beef is a type of salt-cured beef products present in many beef-eating cultures. The English term is used interchangeably in modernity to refer to three distinct types of cured beef:...
.
Sodium nitrateSodium nitrate is the chemical compound with the formula NaNO3. This salt, also known as Chile saltpeter or Peru saltpeter to distinguish it from ordinary saltpeter, potassium nitrate, is a white solid which is very soluble in water...
(and
nitriteSodium nitrite is the inorganic compound with the chemical formula NaNO2. It is a white to slight yellowish crystalline powder that is very soluble in water and is hygroscopic...
) have mostly supplanted potassium nitrate's culinary usage, as they are more reliable in preventing bacterial infection than saltpetre. All three give cured
salamiSalami is cured sausage, fermented and air-dried meat, originating from one of a variety of animals. Historically, salami has been popular among Southern European peasants because it can be stored at room temperature for periods of up to 10 years, supplementing a possibly meager or inconsistent...
and corned beef their characteristic pink hue. When used as a food additive in the European Union, the compound is referred to as
E252E numbers are number codes for food additives that have been assessed for use within the European Union . They are commonly found on food labels throughout the European Union. Safety assessment and approval are the responsibility of the European Food Safety Authority...
; it is also approved for use as a food additive in the USA and Australia and New Zealand (where it is listed under its INS number 252).
Fire extinguishing
Potassium nitrate is the main solid particle component of
condensed aerosol fire suppressionCondensed aerosol fire suppression is a particle-based form of fire extinction similar to gaseous fire suppression or dry chemical fire extinction. The aerosol employs a fire extinguishing agent consisting of very fine solid particles and gaseous matter to put out fires...
systems, but when burned, and interacting with the free radicals of a fire's flame, it produces
potassium carbonatePotassium carbonate is a white salt, soluble in water , which forms a strongly alkaline solution. It can be made as the product of potassium hydroxide's absorbent reaction with carbon dioxide. It is deliquescent, often appearing a damp or wet solid...
.
Tree stump removal
Potassium nitrate is the main component (usually about 98%) of tree stump remover, as it accelerates the natural decomposition of the stump by supplying nitrogen for the fungi attacking the wood of the stump.
Heat treatment of metals
Potassium nitrate is commonly used in the heat treatment of metals as a solvent in the post-wash. The oxidizing, water solubility and low cost make it an ideal short-term rust inhibitor.
Storage for solar energy
Sodium and potassium nitrate salts are stored in molten state with the solar energy collected by the heliostats at the
GEMASOLAR ThermosolarTorresol Energy is a joint venture between SENER and Masdar . It develops solar power tower plants with molten salt technology and parabolic trough power plants....
Plant in Spain. There are ternary salts, with the addition of Calcium Nitrate or Lithium Nitrate, that improves the heat storage capacity in the molten salts
Pharmacology
Potassium nitrate can be found in some
toothpasteToothpaste is a paste or gel dentifrice used with a toothbrush as an accessory to clean and maintain the aesthetics and health of teeth. Toothpaste is used to promote oral hygiene: it serves as an abrasive that aids in removing the dental plaque and food from the teeth, assists in suppressing...
s for
sensitive teethDentine hypersensitivity is sensation felt when the nerves inside the dentin of the teeth are exposed to the environment. The sensation can range from irritation all the way to intense, shooting pain...
. Recently, the use of potassium nitrate in
toothpasteToothpaste is a paste or gel dentifrice used with a toothbrush as an accessory to clean and maintain the aesthetics and health of teeth. Toothpaste is used to promote oral hygiene: it serves as an abrasive that aids in removing the dental plaque and food from the teeth, assists in suppressing...
s for treating sensitive teeth has increased and it may be an effective treatment.
Potassium nitrate in some toothpastes has shown to relieve asthmatic symptoms in some people. It was used in centuries past to treat asthma as well as arthritis.
Potassium nitrate successfully combats high blood pressure and was once used as a hypotensive. Other nitrates and nitrites such as
glyceryl trinitrate (nitroglycerin), amyl nitrite and isosorbide derivatives are still used to relieve
anginaAngina pectoris, commonly known as angina, is chest pain due to ischemia of the heart muscle, generally due to obstruction or spasm of the coronary arteries . Coronary artery disease, the main cause of angina, is due to atherosclerosis of the cardiac arteries...
.
Potassium nitrate was once thought to induce impotence, and is still falsely rumored to be in institutional food (such as military fare) as an
anaphrodisiacAn anaphrodisiac or antiaphrodisiac is something that quells or blunts the libido. It is the opposite of an aphrodisiac, something that enhances sexual appetite...
; however, there is no scientific evidence for such properties.
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