Potassium nitrate

Potassium nitrate
Potassium nitrate[1]
CAS number 7757-79-1 YesY
PubChem 24434
ChemSpider 22843 YesY
UN number 1486
KEGG D02051 YesY
RTECS number TT3700000
Jmol-3D images Image 1
Molecular formula KNO3
Molar mass 101.1032 g/mol
Appearance white solid
Odor odorless
Density 2.109 g/cm3 (16 °C)
Melting point

334 °C

Boiling point

400 °C decomp.

Solubility in water 133 g/L (0 °C)
360 g/L (25 °C)
2470 g/L (100 °C)
Solubility slightly soluble in ethanol
soluble in glycerol, ammonia
Crystal structure Orthorhombic, Aragonite
MSDS External MSDS
EU Index Not listed
EU classification Oxidant (O)
R-phrases R8 R22 R36 R37 R38
S-phrases S7 S16 S17 S26 S36 S41
Main hazards Oxidant, Harmful if swallowed, Inhaled, or absorbed on skin. Causes Irritation to Skin and Eye area.
NFPA 704
NFPA 704.svg
Flash point Non-flammable
LD50 3750 mg/kg
Related compounds
Other anions Potassium nitrite
Other cations Lithium nitrate
Sodium nitrate
Rubidium nitrate
Caesium nitrate
Related compounds Potassium sulfate
Potassium chloride
Supplementary data page
Structure and
n, εr, etc.
Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
 N nitrate (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Potassium nitrate is a chemical compound with the 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. Its common names include saltpetre (saltpeter in American English), from medieval Latin sal petræ: "stone salt" or possibly "Salt of Petra" 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 nitrate.

Major uses of potassium nitrate are in fertilizers, food additive, rocket propellants and fireworks; it is one of the constituents of gunpowder.


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 Syria in his book al-Furusiyya wa al-Manasib al-Harbiyya ('The Book of Military Horsemanship 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 carbonate (in the form of wood ashes) 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.[2] This was used for the manufacture of gunpowder and explosive devices.

Into the 19th century, niter-beds were prepared by mixing manure with either mortar or wood ashes, common earth and organic materials such as straw to give porosity to a compost pile typically 1.5×2×5 meters in size.[3] The heap was usually under a cover from the rain, kept moist with urine, turned often to accelerate the decomposition, then finally leached with water after approximately one year, to remove the soluble calcium nitrate. Dung-heaps were a particularly common source: ammonia from the decomposition of urea 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 potash 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.[3] The nitrate source in this process is calcium nitrate produced by bacterial action on the nitrogenous urea 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 Laos for the manufacture of gunpowder for Bang Fai 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 cordite, a smokeless powder which required in manufacture large quantities of nitric acid derived from mineral nitrates (either potassium nitrate, or increasingly sodium nitrate), and the basic industrial chemical sulfuric acid. These propellants, like all nitrated explosives (nitroglycerine, TNT, etc.) use the energy available when organic nitrates burn or explode and are converted to nitrogen gas, a process that releases large amounts of energy.

From 1903 until the World War I 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 process (1913) was combined with the Ostwald process 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 catalyzes 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.


Potassium nitrate can be made by 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 is highly exothermic.

KOH (aq) + HNO3 → KNO3 (aq) + H2O (l)


The crystal structure of KNO3

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 nitrite, 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 pH 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 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.[4]


Potassium nitrate has a wide variety of uses, largely as a source of nitrate.


Potassium nitrate is mainly used in fertilizers, as a source of nitrogen and potassium – two of the macro nutrients for plants. When used by itself, it has an NPK rating of 13-0-44.


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.[5] As such it is used in black powder rocket motors, but also in combination with other fuels like sugars in "rocket candy". It is also used in fireworks such as smoke bombs, made with a mixture of sucrose and potassium nitrate.[6] It is also added to pre-rolled cigarettes to maintain an even burn of the tobacco[7] and is used to ensure complete combustion of paper cartridges for cap and ball revolvers.[8]

Food preservation

In the process of food preservation, potassium nitrate has been a common ingredient of salted meat since the Middle Ages,[9] 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 charcuterie and the brine used to make corned beef.[10] Sodium nitrate (and nitrite) have mostly supplanted potassium nitrate's culinary usage, as they are more reliable in preventing bacterial infection than saltpetre. All three give cured salami and corned beef their characteristic pink hue. When used as a food additive in the European Union,[11] the compound is referred to as E252; it is also approved for use as a food additive in the USA[12] and Australia and New Zealand[13] (where it is listed under its INS number 252).

Fire extinguishing

Potassium nitrate is the main solid particle component of condensed aerosol fire suppression systems, but when burned, and interacting with the free radicals of a fire's flame, it produces potassium carbonate.

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.[14]

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 Thermosolar 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 [15]


Potassium nitrate can be found in some toothpastes for sensitive teeth.[16] Recently, the use of potassium nitrate in toothpastes for treating sensitive teeth has increased and it may be an effective treatment.[17][18]

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.[citation needed]

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 angina.

Potassium nitrate was once thought to induce impotence, and is still falsely rumored to be in institutional food (such as military fare) as an anaphrodisiac; however, there is no scientific evidence for such properties.[19][20]

See also


  1. ^ Record of Potassium nitrate in the GESTIS Substance Database from the IFA, accessed on 2007-03-09
  2. ^ Ahmad Y Hassan, Potassium Nitrate in Arabic and Latin Sources, History of Science and Technology in Islam.
  3. ^ a b LeConte, Joseph (1862). Instructions for the Manufacture of Saltpeter. Columbia, S.C.: South Carolina Military Department. p. 14. http://docsouth.unc.edu/imls/lecontesalt/leconte.html. Retrieved 2007-10-19. 
  4. ^ B. J. Kosanke, B. Sturman, K. Kosanke, I. von Maltitz, T. Shimizu, M. A. Wilson, N. Kubota, C. Jennings-White, D. Chapman (2004). "2". Pyrotechnic Chemistry. Journal of Pyrotechnics. pp. 5–6. ISBN 1889526150. http://books.google.com/books?id=Q1yJNr92-YcC&pg=PA9. 
  5. ^ Jai Prakash Agrawal (2010). High Energy Materials: Propellants, Explosives and Pyrotechnics. Wiley-VCH. p. 69. ISBN 978-3-527-32610-5. 
  6. ^ Amthyst Galleries, Inc.
  7. ^ Inorganic Additives for the Improvement of Tobacco, TobaccoDocuments.org
  8. ^ Kirst, W.J. (1983). Self Consuming Paper Cartridges for the Percussion Revolver. Minneapolis, Minnesota: Northwest Development Co.. 
  9. ^ "Meat Science", University of Wisconsin
  10. ^ Corned Beef, Food Network
  11. ^ UK Food Standards Agency: "Current EU approved additives and their E Numbers". http://www.food.gov.uk/safereating/chemsafe/additivesbranch/enumberlist. Retrieved 2011-10-27. 
  12. ^ US Food and Drug Administration: "Listing of Food Additives Status Part II". http://www.fda.gov/Food/FoodIngredientsPackaging/FoodAdditives/ucm191033.htm#ftnT. Retrieved 2011-10-27. 
  13. ^ Australia New Zealand Food Standards Code"Standard 1.2.4 - Labelling of ingredients". http://www.comlaw.gov.au/Details/F2011C00827. Retrieved 2011-10-27. 
  14. ^ Roark, Stan. "Stump Removal for Homeowners". Alabama Cooperative Extension System. http://www.aces.edu/homegarden/news/archives/003560.php. Retrieved 2011-09-26. 
  16. ^ "Sensodyne Toothpaste for Sensitive Teeth". 2008-08-03. http://us.sensodyne.com/products_freshmint.aspx. Retrieved 2008-08-03. 
  17. ^ "The Effect of Potassium Nitrate and Silica Dentifrice in the Surface of Dentin". http://sciencelinks.jp/j-east/article/200315/000020031503A0361500.php. Retrieved 2010-07-16. 
  18. ^ Managing dentin hypersensitivity, Robin Orchardson and David G. Gillam, J Am Dent Assoc, Vol 137, No 7, 990-998. 2006
  19. ^ "The Straight Dope: Does saltpeter suppress male ardor?". 1989-06-16. http://www.straightdope.com/classics/a3_221.html. Retrieved 2007-10-19. 
  20. ^ Jones, Richard E.; Kristin H. López (2006). Human Reproductive Biology, Third Edition. Elsevier/Academic Press. p. 225. ISBN 0120884658. http://books.google.com/books?id=pfiZfui2XLIC&pg=PA225. 


  • Dennis W. Barnum. (2003). "Some History of Nitrates." Journal of Chemical Education. v. 80, p. 1393-. link.
  • Alan Williams. "The production of saltpeter in the Middle Ages", Ambix, 22 (1975), pp. 125–33. Maney Publishing, ISSN 0002-6980.

External links