Sodium chloride, also known as salt, common salt, table salt, or halite Halite occurs in vast beds of sedimentary evaporite minerals that result from the drying up of enclosed lakes, playas, and seas. Salt beds may be up to hundreds of meters thick and underlie broad areas. In the United States and Canada extensive underground beds extend from the Appalachian basin of western New York through parts of Ontario and, is an ionic compound In chemistry, an ionic compound is a chemical compound in which ions are held together in a lattice structure by ionic bonds. Usually, the positively charged portion consists of metal cations and the negatively charged portion is an anion or polyatomic ion. Ions in ionic compounds are held together by the electrostatic force between oppositely with the formula A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound Na Sodium is a metallic element with a symbol Na (from Latin natrium or Arabic ناترون natrun; perhaps ultimately from Egyptian netjerj) and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals within "group 1" (formerly known as ‘group IA’). It has only one stable isotope, 23Na Cl The chloride ion is formed when the element chlorine picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. Sodium chloride is the salt In chemistry, salts are ionic compounds that can result from the neutralization reaction of an acid and a base. Salts are ionic compounds composed of cations and anions (negative ions) so that the product is electrically neutral (without a net charge). These component ions can be inorganic such as chloride (Cl−), as well as organic such as most responsible for the salinity of the ocean An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface (~3.61 X 1014 m2) is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas and of the extracellular fluid Extracellular fluid usually denotes all body fluid outside of cells. The remainder is called intracellular fluid of many multicellular organisms In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole. An organism may either be unicellular (single-celled) or be composed of, as in humans, many trillions of cells grouped into. As the major ingredient in edible salt Salt is a dietary mineral composed primarily of sodium chloride that is essential for animal life, but can be toxic to many land plants. Salt flavor is one of the basic tastes, making salt one of the oldest, most ubiquitous food seasonings. Salting is an important method of food preservation, it is commonly used as a condiment A condiment is sauce, or seasoning added to food to impart a particular flavour or to complement the dish. Often pungent in flavour and therefore added in fairly small quantities, popular condiments include salt, pepper, ketchup, mustard, olive oil, vinegar and sugar and food preservative A preservative is a naturally occurring or synthetic substance that is added to products such as foods, pharmaceuticals, paints, biological samples, wood, etc. to prevent decomposition by microbial growth or by undesirable chemical changes.

Production and use

Salt is currently mass-produced Mass production is the production of large amounts of standardized products, including and especially on assembly lines. The concepts of mass production are applied to various kinds of products, from fluids and particulates handled in bulk (such as food, fuel, chemicals, and mined minerals) to discrete solid parts (such as fasteners) to assemblies by evaporation Evaporation is a type of vaporization of a liquid, that occurs only on the surface of a liquid. The other type of vaporization is boiling, that instead occurs on the entire mass of the liquid. Evaporation is also part of the water cycle of seawater Seawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5%. This means that every kilogram, or every litre, of seawater has approximately 35 grams of dissolved salts (mostly, but not entirely, the ions of sodium chloride: Na+, Cl−). The average density of seawater at the ocean surface is 1.025 or brine Brine is water saturated or nearly saturated with a salt . It is used to preserve vegetables, fish, and meat, in a process known as brining (now less popular than historically). Brine is also commonly used to age Halloumi and Feta cheeses. Brine is also used for pickling foodstuffs, as a means of preserving them (or increasing for taste). Almost from other sources, such as brine wells A salt well is used to mine salt from subterranean caverns or deposits by the use of water as a solution to dissolve the salt or halite deposits so that they can be extracted by pipe to an evaporation process that results in a brine or dry product for sale or use. In the 1800s, salt wells were a highly significant source of income for the operator and salt lakes A salt lake or saline lake is a landlocked body of water which has a concentration of salts and other minerals significantly higher than most lakes (often defined as at least three grams of salt per liter). In some cases, salt lakes have a higher concentration of salt than sea water, but such lakes would also be termed hypersaline lakes, and by mining A salt mine is an operation involved in the extraction of salt from rock salt or halite, a type of evaporitic deposit. Areas known for their salt mines include Khewra in Pakistan, Tuzla in Bosnia, Wieliczka and Bochnia in Poland, Hallstatt and Salzkammergut in Austria, Rheinberg in Germany, Slănic in Romania, Provadiya in Bulgaria, Avery Island rock salt, called halite Halite occurs in vast beds of sedimentary evaporite minerals that result from the drying up of enclosed lakes, playas, and seas. Salt beds may be up to hundreds of meters thick and underlie broad areas. In the United States and Canada extensive underground beds extend from the Appalachian basin of western New York through parts of Ontario and. In 2002, world production was estimated at 210 million metric tons The tonne or metric ton (U.S.), also referred to as a metric tonne, is a unit of mass equal to 1,000 kg (2,204.62262 lb) or approximately the mass of one cubic metre of water at four degrees Celsius. It is sometimes abbreviated as mt in the United States, but this conflicts with other SI symbols. The tonne is not a unit in the International System, the top five producers (in million tonnes) being the United States (40.3), China (32.9), Germany (17.7), India (14.5) and Canada (12.3).^[3]

As well as the familiar uses of salt in cooking Cooking is the process of preparing food by applying heat. Cooks select and combine ingredients using a wide range of tools and methods. In the process, the flavor, texture, appearance, and chemical properties of the ingredients can change. Cooking techniques and ingredients vary widely across the world, reflecting unique environmental, economic,, salt is used in many applications, from manufacturing Manufacturing is the use of machines, tools and labor to make things for use or sale. Also it can be used for selling things. The term may refer to a range of human activity, from handicraft to high tech, but is most commonly applied to industrial production, in which raw materials are transformed into finished goods on a large scale. Such pulp and paper, to setting dyes in textiles and fabric, to producing soaps SOAP, originally defined as Simple Object Access Protocol, is a protocol specification for exchanging structured information in the implementation of Web Services in computer networks. It relies on eXtensible Markup Language as its message format, and usually relies on other Application Layer protocols (most notably Remote Procedure Call (RPC) and, detergents A detergent is a material used for cleaning. The term is sometimes used to differentiate between soap and other surfactants used for cleaning, and other bath products. It is the major source of industrial chlorine and sodium hydroxide Sodium hydroxide , also known as lye and caustic soda, is a caustic metallic base. It is used in many industries, mostly as a strong chemical base in the manufacture of pulp and paper, textiles, drinking water, soaps and detergents and as a drain cleaner. Worldwide production in 1998 was around 45 million tonnes.[citation needed] Sodium hydroxide, and used in almost every industry.

Sodium chloride is sometimes used as a cheap and safe desiccant A desiccant is a hygroscopic substance that induces or sustains a state of dryness in its local vicinity in a moderately well-sealed container because it appears to have hygroscopic Hygroscopy is the ability of a substance to attract water molecules from the surrounding environment through either absorption or adsorption properties, making salting Salting is the preservation of food with dry salt. It is related to pickling . It is one of the oldest methods of preserving food, and two historically significant such foods are dried and salted cod (usually referred to as salt fish) and salt-cured meat an effective method of food preservation Food preservation is the process of treating and handling food to stop or greatly slow down spoilage caused or accelerated by micro-organisms. Some methods, however, use benign bacteria, yeasts or fungi to add specific qualities and to preserve food (e.g., cheese, wine). Maintaining or creating nutritional value, texture and flavour is important historically; the salt draws water out of bacteria through osmotic pressure Osmotic pressure is the pressure that must be applied to a solution to prevent the inward flow of water across a semipermeable membrane preventing them from reproducing and causing food to spoil. Even though more effective desiccants are available, few are safe for humans to ingest.

Synthetic uses

Uses of chlorine include PVC Polyvinyl chloride, (IUPAC Poly) commonly abbreviated PVC, is a thermoplastic polymer. It is a vinyl polymer constructed of repeating vinyl groups (ethenyls) having one of their hydrogens replaced with a chloride group, pesticides A pesticide is any substance or mixture of substances intended for preventing, destroying, repelling or mitigating any pest. A pesticide may be a chemical substance, biological agent , antimicrobial, disinfectant or device used against any pest. Pests include insects, plant pathogens, weeds, molluscs, birds, mammals, fish, nematodes (roundworms), and epoxy Epoxy or polyepoxide is a thermosetting polymer formed from reaction of an epoxide "resin" with polyamine "hardener". Epoxy has a wide range of applications, including fiber-reinforced plastic materials and general purpose adhesives 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, and popularly to de-ice driveways and patches of ice.

Firefighting uses

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

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.^[5] Snow removal by addition of salt (salting) is done to make travel easier and safer, and decrease the long term impact 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.^[6]

Biological functions

In humans, a high-salt intake has long been known 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.^[7][8]

Crystal structure

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. 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

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, since 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. 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. The salinity (S) of water is measured as grams salt per kilogram of water, and the freezing temperatures are as follows.

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.^[9] 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.^[10]

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 impact

Road salt ends up in fresh water bodies and could harm aquatic plants and animals by disrupting their osmoregulation ability.^[11] 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.

See also

• 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. ^ Susan R. Feldman. Sodium chloride. Kirk-Othmer Encyclopedia of Chemical Technology. John Wiley & Sons, Inc. Published online, 2005 doi:10.1002/0471238961.1915040902051820.a01.pub2
4. ^ Burgess, J. Metal Ions in Solution (Ellis Horwood, New York, 1978) ISBN 0-85312-027-7
5. ^ 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): 2023–2032. http://www3.interscience.wiley.com/journal/114028130/abstract. Retrieved 2009-07-08.
6. ^ 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.
7. ^ Relationship between Salt Intake, Nitric Oxide and Asymmetric Dimethylarginine and Its Relevance to Patients with End-Stage
8. ^ McCarron, David A. (2008). "Dietary sodium and cardiovascular and renal disease risk factors: dark horse or phantom entry?". Nephrol Dial Transplant 23 (7): 2133–2137. doi:10.1093/ndt/gfn312. PMID 18587159 .
9. ^ "Morton Salt FAQ". http://www.mortonsalt.com/faqs/index.html#q3. Retrieved 2007-05-12.
10. ^ 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. PMID 3541654. PMC 1646845. http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1646845.
11. ^ Does road salt harm the environment?

Further reading

1. Kaufmann, Dale W., SODIUM CHLORIDE, The Production and Properties of Salt and Brine, ACS Monograph 145, American Chemical Society, Washington, D.C., 1960, 743 pages. Library of Congress Catalog Card Number 79-50778.
2. Kurlansky, Mark, SALT, A World History, Walker and Company, New York, 2002, 484 pages. ISBN 0-8027-1373-4

External links

• The Salt Manufacturers Association website
• Salt Institute website
• Salt Archive website
• Salt United States Geological Survey Statistics and Information
• US Road Management website
• Salt Intake in Cold Weather
• Oxford MSDS
• JtBaker MSDS

Categories: Granular materials | Preservatives | Antiseptics | Snow removal | Sodium compounds | Chlorides | World Health Organization essential medicines

See Also:

• Metham Sodium: Encyclopedia
• Organochloride: Encyclopedia
• Carbon Tetrachloride: Encyclopedia
• Sodium Fluoroacetate: Encyclopedia
• Beta-Benzenehexachloride: Encyclopedia

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