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Potassium nitrate is a chemical compound with the chemical formula KNO3. It is an ionic salt of potassium ions K+ and nitrate ions NO3−.
It occurs as a mineral niter and is a natural solid source of nitrogen. Potassium nitrate is one of several nitrogen-containing compounds collectively referred to as saltpeter or saltpetre.
Major uses of potassium nitrate are in fertilizers, tree stump removal, rocket propellants and fireworks. It is one ofthe major constituents of gunpowder (black powder) and has been used since theMiddle Ages as a food preservative.
Potassium nitrate has an orthorhombic crystal structure at room temperature, which transforms to a trigonal system at 129 °C.
Potassium nitrate is moderately soluble inwater, but its solubility increases with temperature (see infobox). The aqueous solution is almost neutral, exhibiting pH 6.2 at 14 °C for a 10% solution of commercial powder. It is not very hygroscopic, absorbing about 0.03% water in80% relative humidity 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.
Between 550 and 790 °C potassium nitrate reaches a temperature dependent equilibrium with potassium nitrite 2 KNO3 ↔ 2 KNO2 +O2
Potassium nitrate can be madeby combining ammonium nitrate and potassium hydroxide.
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 chloride, easily obtained as a sodium-free salt substitute.
NH4NO3 (aq) + KCl (aq) → NH4Cl (aq) + KNO3(aq)
Potassium nitrate can also be produced by neutralizing nitric acid with potassium hydroxide. This reaction ishighly exothermic.
KOH (aq) + HNO3 → KNO3 (aq) + H2O (l)
On industrial scale it is prepared by the double displacement reaction between sodium nitrate and potassium chloride.
NaNO3 (aq) + KCl (aq) → NaCl (aq) + KNO3 (aq)
Potassium nitrate has a widevariety of uses, largely as a source of nitrate.
Nitric acid production
Historically, nitric acid was producedby combining sulfuric acid with nitrates such as saltpeter. In modern timesthis is reversed: nitrates are produced from nitric acid produced via theOstwald process.
The most famous use ofpotassium nitrate is probably as the oxidizer in blackpowder. From the mostancient times through the late 1880s, blackpowder provided the explosive powerfor all the world's firearms. After that time, small arms and large artilleryincreasingly began to depend on cordite, a smokeless powder. Blackpowderremains in use today in black powder rocket motors, but also in combinationwith other fuels like sugars in "rocket candy". It is also used infireworks such as smoke bombs. It is also added to cigarettes to maintain aneven burn of the tobacco and is used to ensure complete combustion of papercartridges for cap and ball revolvers
It can also be heated to several hundreddegrees to be used for niter bluing, which is less durable than other forms ofprotective oxidation, but allows for specific and often beautiful coloration ofsteel parts, such as screws, pins, and other small parts of firearms.
In the process of foodpreservation, potassium nitrate has been a common ingredient of salted meatsince the Middle Ages, but its use has been mostly discontinued because ofinconsistent results compared to more modern nitrate and nitrite compounds.Even so, saltpeter is still used in some food applications, such as charcuterieand the brine used to make corned beef. When used as a food additive in theEuropean Union, the compound is referred to as E252; it is also approved foruse as a food additive in the USA and Australia and New Zealand (where it islisted under its INS number 252). Although nitrate salts have been suspected ofproducing the carcinogen nitrosamine, both sodium and potassium nitrates andnitrites have been added to meats in the US since 1925, and nitrates andnitrites have not been removed from preserved meat products because nitrite andnitrate inhibits the germination of C. botulinum endospores, and thus preventsbotulism from bacterial toxin that may otherwise be produced in certainpreserved meat products.
In West African cuisine,potassium nitrate (salt petre) is widely used as a thickening agent in soups andstews such as Okra soup and Isi ewu. It is also used to soften food and reducecooking time when boiling beans and tough meat. Salt petre is also an essentialingredient in making special porridges such as kunun kanwa literally translatedfrom the Hausa language as 'salt petre porridge'.
Potassium nitrate is used infertilizers as a source of nitrogen and potassium – two of the macronutrientsfor plants. When used by itself, it has an NPK rating of 13-0-44.
Used in some toothpastes for sensitiveteeth.Recently, the use of potassium nitrate in toothpastes for treatingsensitive teeth has increased and it may be an effective treatment.
Used historically to treat asthma.Used in sometoothpastes to relieve asthma symptoms.
Used in Thailand as main ingredient in kidneytablets to relieve the symptoms of cystitis, pyelitis and urethritis.
Combats high blood pressure and was once usedas a hypotensive.
Electrolyte in a salt bridge
Active ingredient of condensed aerosol firesuppression systems. When burned with the free radicals of a fire's flame, itproduces potassium carbonate.
Works as an aluminum cleaner.
Component (usually about 98%) of some treestump removal products. It accelerates the natural decomposition of the stumpby supplying nitrogen for the fungi attacking the wood of the stump.
In heat treatment of metals as a mediumtemperature molten salt bath, usually in combination with sodium nitrite. Asimilar bath is used to produce a durable blue/black finish typically seen onfirearms. Its oxidizing quality, water solubility, and low cost make it anideal short-term rust inhibitor.
To induce flowering of mango trees in thePhilippines.
Thermal storage medium in power generationsystems. Sodium and potassium nitrate salts are stored in a molten state withthe solar energy collected by the heliostats at the Gemasolar ThermosolarPlant. Ternary salts, with the addition of calcium nitrate or lithium nitrate,have been found to improve the heat storage capacity in the molten salts.