Originally Posted by beppe
Potassium nitrate
From Wikipedia, the free encyclopedia
Potassium nitrate[1]
Other names[hide]
Saltpetre
Nitrate of potash
Vesta powder
Identifiers
CAS number 7757-79-1
PubChem 24434
ChemSpider 22843
UN number 1486
RTECS number TT3700000
Properties
Molecular formula KNO3
Molar mass 101.103 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
Structure
Crystal structure Orthorhombic, Aragonite
Hazards
MSDS External MSDS
EU Index Not listed
EU classification Oxidant (O)
NFPA 704
010OX
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
properties n, εr, etc.
Thermodynamic
data Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
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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 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 name Peru saltpetre or Chile saltpetre (American Peru saltpeter or Chile saltpeter) refers not to potassium nitrate but to a similar chemical sodium nitrate. Major uses of potassium nitrate are in fertilizers, rocket propellants and fireworks. When used as a food additive in the European Union, the compound is referred to as E252.
Contents [hide]
1 History of production
2 Properties
3 Uses
4 Pharmacology
5 See also
6 References
7 Bibliography
8 External links
[edit]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'), where he first described the use of potassium carbonate (in the form of wood ashes).[2]
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 and leached with water after approximately one year. 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 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: Stale urine is placed in a container of straw hay and is allowed to sour 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 and air-drying in the sun.[3]
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.
During the 19th century and until around World War I, potassium nitrate was produced on an industrial scale by the Birkeland–Eyde process. Today practically all nitrates are produced from the oxidation of ammonia made by the Haber process.
[edit]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 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]
[edit]Uses
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 also one of the three components of black powder, along with powdered charcoal (substantially carbon) and sulfur, where it acts as an oxidizer.
In the process of food preservation, potassium nitrate has been a common ingredient of salted meat since the Middle Ages,[5] 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.[6] 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.
Potassium nitrate is an efficient oxidizer, which produces a lilac flame upon burning due to the presence of potassium. It is therefore used in amateur rocket propellants and in several fireworks such as smoke bombs.[7] It is also added to pre-rolled cigarettes to maintain an even burn of the tobacco.[8]
Potassium nitrate is the main component (usually about 98%) of tree stump remover, as it accelerates the natural decomposition of the stump.[9] It is also 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.
[edit]Pharmacology
Potassium nitrate can be found in some toothpastes for sensitive teeth.[10] Recently, the use of potassium nitrate in toothpastes for treating sensitive teeth has increased dramatically, despite the fact that it has not been conclusively shown to reduce dentine hypersensitivity.[11]
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.[12][13]
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