luni, 28 martie 2011

Sodium chloride

Sodium chloride

"NaCl".
Sodium chloride

Properties
Molecular formula
NaCl

Molar mass
58.443 g/mol
Appearance Colorless/white crystalline solid
Odor
Odorless
Density
2.165 g/cm3
Melting point
801 °C, 1074 K, 1474 °F
Boiling point
1413 °C, 1686 K, 2575 °F
Solubility in water
356 g/L (0 °C)
359 g/L (25 °C)
391 g/L (100 °C)
Solubility
soluble in glycerol, ethylene glycol, formic acid
insoluble in HCl

Solubility in methanol
14.9 g/L
Solubility in ammonia
21.5 g/L
Acidity (pKa)
6.7–7.3
Refractive index (nD) 1.5442 (589 nm)
Structure
Crystal structure
Face-centered cubic
(see text), cF8

Space group
Fm3m, No. 225
Lattice constant
a = 564.02 pm
Coordination
geometry
Octahedral (Na+)
Octahedral (Cl–)















Sodium chloride, also known as salt, common salt, table salt, or halite, is an ionic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms. As the major ingredient in edible salt, it is commonly used as a condiment and food preservative.
Contents
• 1 Properties
• 2 Production
• 3 Uses
o 3.1 Synthetic uses
o 3.2 Biological uses
o 3.3 Optical uses
o 3.4 Optical data
o 3.5 Household uses
o 3.6 Firefighting uses
o 3.7 In weather
• 4 Biological functions
o 4.1 Veterinary use
• 5 Crystal structure
• 6 Road salt
o 6.1 Additives
o 6.2 Environmental effect
• 7 See also
• 8 References
• 9 External links

Properties
Thermal conductivity of pure NaCl as a function of temperature has a maximum of 2.03 W/(cm K) at 8 K and decreases to 0.069 at 314 K (41 °C). It also decreases with doping.[3]
Production


Modern rock salt mine near Mount Morris, New York, United States
Salt is currently mass-produced by evaporation of seawater or brine from other sources, such as brine wells and salt lakes, and by mining rock salt, called halite. In 2010, world production was estimated at 270 million metric tons, the top five producers (in million tonnes) being China (60.0), United States (45.0), Germany (16.5), India (15.8) and Canada (14.0).[4]
Uses
As well as the familiar uses of salt in cooking, salt is used in many applications, from manufacturing pulp and paper, to setting dyes in textiles and fabric, to producing soaps, detergents, and other bath products. It is the major source of industrial chlorine and sodium hydroxide, and used in almost every industry.
Sodium chloride is sometimes used as a cheap and safe desiccant because of its hygroscopic properties, making salting an effective method of food preservation historically; the salt draws water out of bacteria through osmotic pressure, keeping it from reproducing, a major source of food spoilage. Even though more effective desiccants are available, few are safe for humans to ingest.
Solubility of NaCl in various solvents
(g NaCl / 1 kg of solvent at 25 °C)[5]

H2O
360
Formamide
94
glycerin
83
propylene glycol
71
Formic acid
52
Liquid ammonia
30.2
Methanol
14
Ethanol
0.65
Dimethylformamide
0.4
1-propanol
0.124
Sulfolane
0.05
1-butanol
0.05
2-propanol
0.03
1-pentanol
0.018
Acetonitrile
0.003
Acetone
0.00042
[edit] Synthetic uses
Uses of chlorine include PVC, pesticides and epoxy resins. Industrially, elemental chlorine is usually produced by the electrolysis of sodium chloride dissolved in water. Along with chlorine, this chloralkali process yields hydrogen gas and sodium hydroxide, according to the chemical equation
2 NaCl + 2 H2O → Cl2 + H2 + 2 NaOH
Sodium metal is produced commercially through the electrolysis of liquid sodium chloride. This is now done in a Down's cell in which sodium chloride is mixed with calcium chloride to lower the melting point below 700 °C. As calcium is more electropositive than sodium, no calcium will be formed at the cathode. This method is less expensive than the previous method of electrolyzing sodium hydroxide.
Sodium chloride is used in other chemical processes for the large-scale production of compounds containing sodium or chlorine. In the Solvay process, sodium chloride is used for producing sodium carbonate and calcium chloride. In the Mannheim process and in the Hargreaves process, it is used for the production of sodium sulfate and hydrochloric acid.
Biological uses
Many micro organisms cannot live in an overly salty environment: water is drawn out of their cells by osmosis. For this reason salt is used to preserve some foods, such as smoked bacon or fish. It can also be used to detach leeches that have attached themselves to feed. It is also used to disinfect wounds.
Optical uses
Pure NaCl crystal is an optical compound with a wide transmission range from 200 nm to 20 µm. It was often used in the infrared spectrum range and it is still used sometimes.
While inexpensive, NaCl crystal is soft and hygroscopic. When exposed to free air, NaCl optics gradually covers with "frost". This limits application of NaCl to protected environments or for short-term uses such as prototyping.
Today tougher crystals like zinc selenide (ZnSe) are used instead of NaCl (for the IR spectral range).
Optical data
• Transmitivity: 92% (from 400 nm to 13 μm)
• Refractive Index: 1.494 at 10 μm
• Reflection Loss: 7.5% at 10 μm (2 surfaces)
• dN/dT: −36.2×10−6/°C at 0.7 μm
Household uses
Since at least medieval times, people have used salt as a cleansing agent rubbed on household surfaces. It is also used in many brands of shampoo,toothpaste and popularly to de-ice driveways and patches of ice.
Firefighting uses


A class D fire extinguisher for various metals
Sodium chloride is the principal extinguishing agent in fire extinguishers (Met-L-X, Super D) used on combustible metal fires such as magnesium, potassium, sodium, and NaK alloys (Class D). Thermoplastic powder is added to the mixture, along with waterproofing (metal stearates) and anti-caking materials (tricalcium phosphate) to form the extinguishing agent. When it is applied to the fire, the salt acts like a heat sink, dissipating heat from the fire, and also forms an oxygen-excluding crust to smother the fire. The plastic additive melts and helps the crust maintain its integrity until the burning metal cools below its ignition temperature. This type of extinguisher was invented in the late 1940s in the cartridge-operated type shown here, although stored pressure versions are now popular. Common sizes are 30 lb. portable and 350 lb. wheeled.
In weather


Clouds above the Pacific
Small particles of sea salt are the dominant cloud condensation nuclei well out at sea, which allow the formation of clouds in otherwise non-polluted air.[6] Snow removal by addition of salt (salting) is done to make travel easier and safer, and decrease the long term effect of a heavy snowfall on human populations. This process is done by both individual households and by governments and institutions and utilizes salts to eliminate snow from road surfaces and sidewalks.[7]
Biological functions
For further information about sodium chloride in the diet, see Salt.
In humans, a high-salt intake has long been suspected to generally raise blood pressure. More recently, it was demonstrated to attenuate nitric oxide production. Nitric oxide (NO) contributes to vessel homeostasis by inhibiting vascular smooth muscle contraction and growth, platelet aggregation, and leukocyte adhesion to the endothelium.[8][9]
Veterinary use
Sodium chloride is used in veterinary medicine as emesis causing agent. It is given as warm saturated solution. Emesis can also be caused by pharyngeal placement of small amount of plain salt or salt crystals.
Crystal structure


The crystal structure of sodium chloride. Each ion has six nearest neighbors, with octahedral geometry.
Main article: Cubic crystal system
Sodium chloride forms crystals with face-centered cubic symmetry. In these, the larger chloride ions, shown to the right as green spheres, are arranged in a cubic close-packing, while the smaller sodium ions, shown to the right as silver spheres, fill all the cubic gaps between them. Each ion is surrounded by six ions of the other kind; the surrounding ions are located at the vertices of a regular octahedron. This same basic structure is found in many other minerals and is commonly known as the halite or rock-salt crystal structure. It can be represented as a face-centered cubic (fcc) lattice with a two atom basis or as two interpenetrating face centered cubic lattices. The first atom is located at each lattice point, and the second atom is located half way between lattice points along the fcc unit cell edge.
It is held together by an ionic bond which is produced by electrostatic forces arising from the difference in charge between the ions.
Road salt


Phase diagram of water-NaCl mixture.
While salt was once a scarce commodity in history, industrialized production has now made salt plentiful. Approximately 51% of world output is now used by cold countries to de-ice roads in winter, both in grit bins and spread by winter service vehicles. Calcium chloride is preferred over sodium chloride, as CaCl2 releases energy upon forming a solution with water, heating any ice or snow it is in contact with. It also lowers the freezing point, depending on the concentration (see image and data table). Whereas the minimum freezing point is −21.12 °C for 23.31 wt% of salt, the freezing near this concentration is so slow that the eutectic point of −22.4 °C can be reached with about 25 wt% of salt.[10] NaCl does not release heat upon solution; however, it does lower the freezing point. Calcium chloride is thought to be more environmentally friendly than sodium chloride when used to de-ice roads, however a drawback is that it tends to promote corrosion (of vehicles) more so than sodium chloride. NaCl is also more readily available and does not have any special handling or storage requirements, unlike calcium chloride.
Additives
Most table salt sold for consumption today is not pure sodium chloride. In 1911, magnesium carbonate was first added to salt to make it flow more freely.[11] In 1924, trace amounts of iodine in form of sodium iodide, potassium iodide or potassium iodate were first added, to reduce the incidence of simple goiter.[12]
Salt for de-icing in the United Kingdom predominantly comes from a single mine in Winsford in Cheshire. Prior to distribution it has an anti-caking agent added: sodium hexacyanoferrate(II) at less than 100 ppm. This treatment enables rock salt to flow freely out of the gritting vehicles despite being stockpiled prior to use. In recent years this additive has also been used in table salt.
Environmental effect
Road salt ends up in fresh water bodies and could harm aquatic plants and animals by disrupting their osmoregulation ability.[13] An alternative is to spread rough sand on ice so the surface is not slippery.
The omnipresence of salt posts a problem in any coastal coating application, as trapped salts cause great problems in adhesion. Costs can reach staggering amounts. Naval authorities and ship builders keep a close eye on salt concentrations on surfaces during construction. Maximum salt concentrations on surfaces are dependent on the authority and application. The IMO regulation is mostly used and sets salt levels to a maximum of 50 mg/m2 soluble salts measured as sodium chloride. These measurements are done by means of a Bresle test.

Israeli and Jordanian salt evaporation ponds at the south end of the Dead Sea.

Mounds of salt, Salar de Uyuni, Bolivia.

Evaporation lagoons, Aigues-Mortes, France.
See also
Wikibooks Cookbook has a recipe/module on
Salt

• Biosalinity
• Kala Namak
• Halite, the mineral form of sodium chloride
• Salinity
• Salt
• Soap
• Salting the earth
References
1. ^ National Institute of Standards and Technology: Sodium Chloride
2. ^ Martel, B.; Cassidy, K. (2004). Chemical Risk Analysis: A Practical Handbook. Butterworth–Heinemann. p. 369. ISBN 1903996651.
3. ^ Dinker B. Sirdeshmukh, Lalitha Sirdeshmukh, K. G. Subhadra (2001). Alkali halides: a handbook of physical properties. Springer. pp. 65, 68. ISBN 3540421807. http://books.google.com/books?id=X-yL7EgMK6wC&pg=PA68.
4. ^ Salt, U.S. Geological Survey
5. ^ Burgess, J. (1978). Metal Ions in Solution. New York: Ellis Horwood. ISBN 0-85312-027-7.
6. ^ B. J. Mason (2006-12-19). "The role of sea-salt particles as cloud condensation nuclei over the remote oceans". The Quarterly Journal of the Royal Meteorological Society 127 (576): 2023–32. doi:10.1002/qj.49712757609. http://www3.interscience.wiley.com/journal/114028130/abstract.
7. ^ David A. Kuemmel (1994). Managing roadway snow and ice control operations. Transportation Research Board. p. 10. ISBN 9780309056663. http://books.google.com/?id=I3gxuwTE5_MC&pg=PA10&lpg=PA10&dq=effect+of+snowfall+on+infrastructure. Retrieved 2009-07-08.
8. ^ Osanai T, Fujiwara N, Saitoh M, et al. (2002). "Relationship between salt intake, nitric oxide and asymmetric dimethylarginine and its relevance to patients with end-stage renal disease". Blood Purif. 20 (5): 466–8. doi:10.1159/000063555. PMID 12207094. http://content.karger.com/produktedb/produkte.asp?typ=fulltext&file=bpu20466.
9. ^ McCarron, David A. (2008). "Dietary sodium and cardiovascular and renal disease risk factors: dark horse or phantom entry?". Nephrol Dial Transplant 23 (7): 2133–7. doi:10.1093/ndt/gfn312. PMC 2441768. PMID 18587159. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2441768.
10. ^ Elvers, B. et al. (ed.) (1991) Ullmann's Encyclopedia of Industrial Chemistry, 5th ed. Vol. A24, Wiley, p. 319
11. ^ "Morton Salt FAQ". http://www.mortonsalt.com/faqs/index.html#q3. Retrieved 2007-05-12.
12. ^ Markel H (1987). ""When it rains it pours": endemic goiter, iodized salt, and David Murray Cowie, MD". American journal of public health 77 (2): 219–29. doi:10.2105/AJPH.77.2.219. PMC 1646845. PMID 3541654. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1646845.
13. ^ Does road salt harm the environment?
External links
Wikimedia Commons has media related to: Sodium chloride

• The Salt Manufacturers Association website
• Salt Institute website
• Salt Archive website
• Salt United States Geological Survey Statistics and Information
• "Using Salt and Sand for Winter Road Maintenance". Road Management Journal. December 1997. http://www.usroads.com/journals/p/rmj/9712/rm971202.htm.
• Dejima Y, Fukuda S, Ichijoh Y, Takasaka K, Ohtsuka R (June 1996). "Cold-induced salt intake in mice and catecholamine, renin and thermogenesis mechanisms". Appetite 26 (3): 203–19. doi:10.1006/appe.1996.0016. PMID 8800478. http://linkinghub.elsevier.com/retrieve/pii/S0195-6663(96)90016-1. — Salt Intake in Cold Weather
• Oxford MSDS
• JtBaker MSDS
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Un comentariu:

  1. -Ce bine le zici tu!?!Vrei sa crezi ca faci reclama?Incearca sa si bei in loc de H@O...???

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