Sodium nitrate

Sodium nitrate

Names
IUPAC name Sodium nitrate
Other names Caliche Chile saltpeter Nitrate of soda Nitratine Peru saltpeter Soda niter cubic niter
Identifiers
CAS Number	7631-99-4 Y
3D model (Jmol)	Interactive image
ChEMBL	ChEMBL1644698 N
ChemSpider	22688 Y
ECHA InfoCard	100.028.686
EC Number	231-554-3
E number	E251 (preservatives)
PubChem	24268
RTECS number	WC5600000
UNII	8M4L3H2ZVZ Y
UN number	1498
InChI InChI=1S/NO3.Na/c2-1(3)4;/q-1;+1 Y Key: VWDWKYIASSYTQR-UHFFFAOYSA-N Y InChI=1/NO3.Na/c2-1(3)4;/q-1;+1 Key: VWDWKYIASSYTQR-UHFFFAOYAL
SMILES [Na+].[O-][N+]([O-])=O
Properties
Chemical formula	NaNO3
Molar mass	84.9947 g/mol
Appearance	White powder or colorless crystals
Odor	sweet
Density	2.257 g/cm3, solid
Melting point	308 °C (586 °F; 581 K)
Boiling point	380 °C (716 °F; 653 K) decomposes
Solubility in water	73 g/100 mL (0 °C) 91.2 g/100 mL (25 °C) 180 g/100 mL (100 °C)
Solubility	very soluble in ammonia, hydrazine soluble in alcohol slightly soluble in pyridine insoluble in acetone
Refractive index (nD)	1.587 (trigonal) 1.336 (rhombohedral)
Viscosity	2.85 cP (317 °C)
Structure
Crystal structure	trigonal and rhombohedral
Thermochemistry
Specific heat capacity (C)	93.05 J/(mol K)
Std molar entropy (So298)	116 J/(mol K)[1]
Std enthalpy of formation (ΔfHo298)	−467 kJ/mol[1]
Gibbs free energy (ΔfG˚)	−365.9 kJ/mol
Hazards
Main hazards	Oxidant, irritant
Safety data sheet	ICSC 0185
EU classification (DSD)	O
NFPA 704	0 1 0 OX
Flash point	Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (median dose)	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
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Sodium nitrate is the chemical compound with the formula NaNO₃. This alkali metal nitrate salt is also known as Chile saltpeter or Peru saltpeter (due to the large deposits found in the Atacama desert in these countries) to distinguish it from ordinary saltpeter, potassium nitrate. The mineral form is also known as nitratine, nitratite or soda niter.

Sodium nitrate is a white solid very soluble in water. It is a readily available source of the nitrate anion (NO₃⁻), which is useful in several reactions carried out on industrial scales for the production of fertilizers, pyrotechnics and smoke bombs, glass and pottery enamels, food preservatives (esp. meats), and solid rocket propellant. It has been mined extensively for these purposes.

History

The first shipment of Peruvian saltpeter to Europe arrived in England in 1820 or 1825, right after that country's independence from Spain, but did not find any buyers and was dumped at sea in order to avoid customs toll.^[2][3] With time, however, the mining of South American saltpeter became a profitable business (in 1859, England alone consumed 47,000 metric tons^[3]). Chile fought against the allies Peru and Bolivia in the War of the Pacific 1879-1884 and took over their richest deposits. In 1919, Ralph Walter Graystone Wyckoff determined its crystal structure using X-ray crystallography.

Sources

The largest accumulations of naturally occurring sodium nitrate are found in Chile and Peru, where nitrate salts are bound within mineral deposits called caliche ore.^[4] Nitrates accumulate on land through marine-fog precipitation and sea-spray oxidation/desiccation followed by gravitational settling of airborne NaNO₃, KNO₃, NaCl, Na₂SO₄, and I, in the hot-dry desert atmosphere.^[5] El Niño/La Niña extreme aridity/torrential rain cycles favor nitrates accumulation through both aridity and water solution/remobilization/transportation onto slopes and into basins; capillary solution movement forms layers of nitrates; pure nitrate forms rare veins. For more than a century, the world supply of the compound was mined almost exclusively from the Atacama desert in northern Chile until, at the turn of the 20th century, German chemists Fritz Haber and Carl Bosch developed a process for producing ammonia from the atmosphere on an industrial scale (see Haber process). With the onset of World War I, Germany began converting ammonia from this process into a synthetic Chilean saltpeter, which was as practical as the natural compound in production of gunpowder and other munitions. By the 1940s, this conversion process resulted in a dramatic decline in demand for sodium nitrate procured from natural sources.

Chile still has the largest reserves of caliche, with active mines in such locations as Pedro de Valdivia, María 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 sodium carbonate or sodium bicarbonate:

2 HNO₃ + Na₂CO₃ → 2 NaNO₃ + H₂O + CO₂

HNO₃ + NaHCO₃ → NaNO₃ + H₂O + CO₂

or also by neutralizing it with sodium hydroxide (however, this reaction is very exothermic):

HNO₃ + NaOH → NaNO₃ + H₂O

or by mixing stoichiometric amounts of ammonium nitrate and sodium hydroxide, sodium bicarbonate or sodium carbonate:

NH₄NO₃ + NaOH → NaNO₃ + NH₄OH

NH₄NO₃ + NaHCO₃ → NaNO₃ + NH₄HCO₃

2NH₄NO₃ + Na₂CO₃ → 2NaNO₃ + (NH₄)₂CO₃

Applications

Sodium nitrate was used extensively as a fertilizer and a raw material for the manufacture of gunpowder in the late 19th century. It can be combined with iron hydroxide to make a synthetic resin.

Sodium nitrate can be combined with sulfuric acid and nitric acid distilled off. At lower pressure the lower temperature needed results in less decomposition. The theoretical 2 moles of nitric acid per 1 mole of sulfuric acid results in a very high end temperature, much decomposition and a solid neutral sulfate that is difficult to remove. When this reaction was important industrially, it was common practice to operate with sulfuric acid in excess to end on a mostly bisulfate product poured molten out of the retort.

Hobbyist gold refiners use sodium nitrate to make a hybrid aqua regia that dissolves gold and other metals.

Sodium nitrate is also a food additive used as a preservative and color fixative in cured meats and poultry; it is listed under its INS number 251 or E number E251. It is approved for use in the EU,^[6] USA^[7] and Australia and New Zealand.^[8] Sodium nitrate should not be confused with sodium nitrite, which is also a common food additive and preservative used, for example, in deli meats.

Less common applications include as an oxidizer in fireworks, replacing potassium nitrate commonly found in black powder, and as a component in instant cold packs.^[9]

Sodium nitrate is used together with potassium nitrate and calcium nitrate for heat storage and, more recently, for heat transfer in solar power plants. A mixture of sodium nitrate, calcium nitrate and potassium nitrate is used as energy-storage material in prototype plants, such as Andasol Solar Power Station and the Archimedes project.

It is also used in the wastewater industry for facultative microorganism respiration. Nitrosomonas, a genus of microorganisms, consumes nitrate in preference to oxygen, enabling it to grow more rapidly in the wastewater to be treated.

Sodium nitrate is also sometimes used by marine aquarists who utilize carbon-dosing techniques. It is used to increase nitrate levels in the water and promote bacterial growth.

Dental use

Mouthwash and gels containing sodium nitrate are used in treatment of dentine hypersensitivity.

Health concerns

Advertisement for sodium nitrate fertilizer from Chile on a wall of a village in the Algarve area of Portugal

Studies have shown a link between increased levels of nitrates and increased deaths from certain diseases including Alzheimer's, diabetes mellitus, Gastric Cancer, and Parkinson's: possibly through the damaging effect of nitrosamines on DNA, however, little is done to control for other possible causes in the epidemiological results.^[10] Nitrosamines, formed in cured meats containing sodium nitrate and nitrite, have been linked to gastric cancer and oesophageal cancer.^[11] Sodium nitrate and nitrite are associated with a higher risk of colorectal cancer.^[12]

One of the reasons that processed meat increases the risk of colon cancer is its content of nitrate. A small amount of the nitrate added to meat as a preservative breaks down into nitrite, in addition to any nitrite that may also be added. The nitrite then reacts with protein-rich foods (such as meat) to produce carcinogenic NOCs (nitroso compounds). NOCs can be formed either when meat is cured or in the body as meat is digested.^[13]

For most people, the highest dietary source of nitrates is from fruits and vegetables and no studies have conclusively linked nitrates and nitrites to cancer or any other form of diseases. On the contrary, some research has hinted to beneficial properties of nitrites such as lowering blood pressure by slightly expanding arteries.^[14] The only reason nitrates and nitrites came under such legal scrutiny is when the US Food and Drug Administration presented a brief report which stated that some adverse effect was observed on mice (“depression of growth”) when their intake of nitrites was up to 90% of daily diet.^[15]

See also

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

Notes and references

Further reading

• Barnum, Dennis (2003). "Some History of Nitrates". Journal of Chemical Education. 80: 1393–. doi:10.1021/ed080p1393. 

External links

• ATSDR — Case Studies in Environmental Medicine - Nitrate/Nitrite Toxicity U.S. Department of Health and Human Services (public domain)
• FAO/WHO report
• Calculators: surface tensions, and densities, molarities and molalities of aqueous sodium nitrate