sodium nitrate

A nitrate mineral having chemical composition NaNO₃ (sodium nitrate); also known as nitratite, it is by far the most abundant of the nitrate minerals. It sometimes occurs as simple rhombohedral crystals but is usually massive granular. The mineral has a perfect rhombohedral cleavage, conchoidal fracture, and is rather sectile. Its hardness is 1.5 to 2 on Mohs scale, and its specific gravity is 2.266. It has a vitreous luster and is transparent. It is colorless to white, but when tinted by impurities, it is reddish brown, gray, or lemon yellow. See also Hardness scales.

Soda niter is a water-soluble salt found principally as a surface efflorescence in arid regions, or in sheltered places in wetter climates. It is usually associated with niter, nitrocalcite, gypsum, epsomite, mirabilite, and halite. The only large-scale commercial deposits of soda niter in the world occur in a belt roughly 450 mi (725 km) long and 10–50 mi (16–80 km) wide along the eastern slope of the coast ranges in the Atacama, Tarapaca, and Antofagasta Deserts of northern Chile. Chilean nitrate had a monopoly of the world's fertilizer market for many years, but now occupies a subordinate position owing to the development of synthetic processes for nitrogen fixation which permit the production of nitrogen from the air. See also Caliche; Fertilizer; Niter; Nitrate minerals.

Environment

Residual water-soluble surface deposits in deserts, primarily in Chile.

Usually in white masses; cavities sometimes have rhombohedral crystals, resembling calcite.

Colorless, white, soil tinted red-brown, or yellow. Luster glassy; hardness 1Ɖ-2; specific gravity : 2.2-2.3; fracture conchoidal; cleavage perfect rhombohedral. Slightly sectile; transparent to translucent.

Sodium nitrate (36.5% Na ₂ O, 63.5% N ₂ O ₃ ).

Burns, with spurt of yellow flame when dropped on glowing spot in charcoal. Dissolves in water, tastes cooling to the tongue. Heated in closed tube with potassium disulfate, gives off brown fumes (nitric oxide, NO).

The deflagration on coals shows it to be a nitrate, and the yellow flame color shows the sodium. Could only be confused with halite, which only melts on the hot charcoal.

Once abundant on the desert surface in beds--composed principally of gypsum, halite, soda niter, some iodides, and other related minerals--in the world's driest region, the Atacama desert, Chile, just west of the Andes. Small quantities of nitrates are reported in some of the dry California lake beds and in Humboldt Co., Nevada. Small amounts are still scavenged in Chile for use in fertilizers, but the once-rich layers from the heyday of nitrate mining are now only to be seen sealed up in museum jars. At the Chilean refinery, a violet iodine vapor floats from the retort.

Its crystal network is identical in character and dimensions with that of calcite. Soda niter crystals in exact parallel position can be grown on the surface of calcite rhombohedrons from saturated solutions of soda niter. Discarded specimens of this mineral tossed in a monastery garden led to the discovery of the importance of nitrogen to plant growth.

Sodium nitrate
IUPAC name	Sodium nitrate
Other names	Caliche Chile saltpeter Nitrate of soda Nitratine Peru saltpeter Soda niter
Identifiers
CAS number	7631-99-4 Y
PubChem	24268
UN number	1498
RTECS number	WC5600000
Properties
Molecular formula	NaNO3
Molar mass	84.9947 g/mol
Appearance	White powder or colorless crystals with sweet smell
Density	2.257 g/cm3, solid
Melting point	308 °C
Boiling point	380 °C decomp.
Solubility in water	92.1 g/100 ml (25 °C) 180 g/100mL (100 °C)
Solubility	very soluble in ammonia; soluble in alcohol
Refractive index (nD)	1.587 (trigonal) 1.336 (rhomobohedral)
Structure
Crystal structure	trigonal and rhombohedral
Thermochemistry
Std enthalpy of formation ΔfHo298	−468 kJ/mol
Standard molar entropy So298	117 J mol−1 K−1
Hazards
MSDS	ICSC 0185
EU Index	Not listed
Main hazards	Oxidant, irritant
NFPA 704	0 1 0 OX
Flash point	Non-flammable
LD50	3236 mg/kg
Related compounds
Other anions	Sodium nitrite
Other cations	Lithium nitrate Potassium nitrate Rubidium nitrate Caesium nitrate
Related compounds	Sodium sulfate Sodium chloride
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Sodium 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. The mineral form is also known as nitratine or soda niter.

Sodium nitrate is used as an ingredient in fertilizers, pyrotechnics, as a food preservative, and as a solid rocket propellant, as well as in glass and pottery enamels; the compound has been mined extensively for those purposes.

The mining of South American saltpeter was such a profitable business that Chile fought against the allies Peru and Bolivia and took over the richest deposits in the War of the Pacific. The world's largest natural deposits of caliche ore were in the Atacama desert of Chile, and many deposits were mined for over a century, until the 1940s, when its value declined dramatically in the first decades of the twentieth century (see Haber process).

Chile still has the largest reserves of caliche, with active mines in such locations as Pedro de Valdivia, Maria Elena and Pampa Blanca, and there it used to be called "white gold". Sodium nitrate, potassium nitrate, sodium sulfate and iodine are all obtained by the processing of caliche. The former Chilean saltpeter mining communities of Humberstone and Santa Laura were declared Unesco World Heritage sites in 2005.

Sodium nitrate is also synthesized industrially by neutralizing nitric acid with soda ash.

Contents 1 Applications 2 See also 3 Notes and references 4 Further reading 5 External links

Applications

Sodium nitrate was used extensively as a fertilizer and a raw material for the manufacture of gunpowder in the late nineteenth century. Sodium nitrate has antimicrobial properties when used as a food preservative. It is found naturally in leafy green vegetables. It can also be combined with iron hydroxide to make a resin.

Sodium nitrate should not be confused with the related compound, sodium nitrite.

It can be used in the production of nitric acid by combining it with sulfuric acid and subsequent separation through fractional distillation of the nitric acid, leaving behind a residue of sodium bisulfate. Hobbyist gold refiners use sodium nitrate to make a hybrid aqua regia that dissolves gold and other metals.

Less common applications include its use as a substitute oxidizer used in fireworks as a replacement for potassium nitrate commonly found in black powder and as a component in instant cold packs.^[1]

Because sodium nitrate can be used as a Phase Change Material it may be used for heat transfer in solar power plants.

It is also used in the wastewater industry for the faculative microrganisms respiration. The growth of nitrosomines will use the nitrate instead of oxygen to breath easier.

See also

• War of the Pacific, also known as the "Saltpeter War"

Notes and references

1. ^ "US patent 2,898,744". http://www.google.com/patents?id=HUcCAAAAEBAJ. 

Further reading

• Barnum, Dennis (2003). "Some History of Nitrates". Journal of Chemical Education 80: 1393–. http://jchemed.chem.wisc.edu/Journal/Issues/2003/Dec/abs1393.html. 

External links

• ATSDR — Case Studies in Environmental Medicine - Nitrate/Nitrite Toxicity U.S. Department of Health and Human Services (public domain)
• FAO/WHO report
• Why Nitrates are important to health.

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