|__ Na + __ Cl -|
Fm 3 m (No. 225)
a = 564.00 pm
Na , Cl 
colorless and odorless solid
|External identifiers / databases|
|Molar mass||58.44 g mol −1|
801 ° C
1461 ° C
good in water (358 g l −1 at 20 ° C), soluble in methanol (1.31 g / 100 g) and ethanol (0.065 g / 100 g at 25 ° C)
1.55 (500 nm)
|As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C|
Sodium chloride (also known as common salt ) is the sodium salt of hydrochloric acid with the chemical formula NaCl - not to be confused with sodium chlorite (NaClO 2 ), the sodium salt of chlorous acid .
Sodium chloride is the most important mineral for humans and animals . An adult human body contains around 150–300 g of table salt and loses 3–20 grams of it every day, which must be replaced. It was won for this in prehistoric times and remained an expensive commodity for a long time.
Sodium chloride is naturally present in large quantities, mostly dissolved in sea water with a content of approx. 3%, a total of 3.6 · 10 16 tons, and also as a mineral halite with a content of up to 98% in the frequent rock salt deposits , the in geological time sedimented in drying sea bays. The total deposits under Germany are estimated to have a volume of 100,000 cubic kilometers.
Rock salt layers are plastic and are therefore often deformed by geological processes to which they are subject, u. a. to more easily degradable salt domes and salt pillows. If a salt deposit in the mountains emerges to the surface, a salt glacier can even form.
Sodium chloride is obtained on a large scale from the two main deposits of rock salt and sea salt . Salt from aboveground deposits, e.g. B. salt lakes, is of little importance. World salt production in 2006 was over 250 million tons, the proportions of rock and sea salt are estimated at around 70% and 30%, respectively. The six largest producers of the year 2006 with together over 60% of the production are given in the table below. China has increased its production considerably in recent years; the USA had the largest production until 2005. Overall, the EU produces similar quantities to the USA.
In salt mines , among which open-cast mines are of little quantitative importance today, rock salt is mined either by drilling, blasting, cutting or wet. In the first two cases, the material , which has been crushed underground with crushers, is brought to the surface in various grain sizes. In wet mining (English: liquid mining ), as in the case of borehole extraction operated exclusively from above ground, the salt is dissolved in water by means of drilling flushing works , historically also in sinks , and extracted as saturated brine of 26.5%. This also allows the use of heavily contaminated deposits. With natural water penetration through salt-bearing layers, brine can also come to light, which is usually not saturated. Such brine springs were the first salt deposits used by humans in the interior. In the past, the concentration was increased by means of graduation towers through water evaporation; today, dry mined salt is added. The purified brine, which can also be made from dry rock salt, is evaporated to produce high-purity evaporated salt . Today this is done by means of closed vacuum evaporators arranged in cascades , whereby a large part of the heat used is recovered. In climatically suitable areas, solar energy is increasingly used for evaporation, the process is comparable to that of sea salt extraction.
The extraction of salt from seawater is only economical in coastal areas with high solar radiation and low rainfall. The sea water is led through shallow basin cascades ( salt gardens ) in which the salt concentration increases through natural evaporation. Finally, the precipitated salt is pushed together and dried, only for the expensive table salt quality fleur de sel it is skimmed off floating on the surface. Brine can also be extracted from salt gardens.
The four basic products of the salt industry are brine, rock salt, sea salt and vacuum salt. For the USA, the US Geological Survey estimated average ex-works prices of USD 10 / t for brine, USD 25 / t for rock salt, USD 57 / t for salt from solar evaporation and USD 150 / t for vacuum salt for 2007.
(in million t )
|1||People's Republic of China||68.0|
Sodium chloride forms colorless crystals that form a cubic sodium chloride structure . In contrast to many other crystals, they are not birefringent. Here, each sodium and each chlorine nucleus is octahedral surrounded by the other nucleus. A hexagonal structure can be produced in a thin layer on a diamond surface. It is very soluble in water, the solubility being only slightly dependent on temperature.
|Solubility in water as a function of temperature|
|temperature||in ° C||0||20th||40||60||80||100|
|solubility||in g / 100 g water||35.76||35.92||36.46||37.16||37.99||39.12|
|Max. Mass concentration||in g · l −1||318.5||317.1||318.2||320.5||323.3||327.9|
|density||in g cm −3||1.2093||1.1999||1.1914||1.1830||1.1745||1.1660|
According to Raoult's law , the vapor pressure of aqueous solutions is lower than that of pure water. The effect increases with increasing sodium chloride concentration or temperature. The saturated solution boils at 108.7 ° C.
|Vapor pressure of aqueous sodium chloride solutions|
|Concentration in Ma%||5||10||15th||20th||25th|
|Vapor pressure in kPa||0 ° C||0.59||0.57||0.55||0.51||0.47|
|20 ° C||2.26||2.18||2.09||1.97||1.81|
|40 ° C||7.13||6.88||6.58||6.20||5.72|
|60 ° C||19.26||18.58||17.78||16.76||15.33|
|80 ° C||45.75||44.16||42.49||39.97||37.09|
|100 ° C||97.89||94.43||90.44||85.52||79.67|
The quotient of the vapor pressure of an aqueous sodium chloride solution and the vapor pressure of pure water is the relative equilibrium humidity at the relevant concentration and temperature. Because of the lower vapor pressure, the relative equilibrium humidity in the air above the solution is less than 100%.
As long as there is undissolved sediment in a saturated solution, the solution keeps its concentration and thus the equilibrium moisture content constant. Such a saturated solution is therefore suitable, for example, for generating a fixed humidity point for calibrating hygrometers. If the ambient humidity is increased beyond the equilibrium humidity, there is supersaturation and air humidity condenses on the liquid surface until the relative ambient humidity has fallen back to the equilibrium value. The associated dilution of the solution is compensated by the fact that part of the undissolved sediment goes into solution.
|Relative equilibrium humidity over saturated sodium chloride solutions|
|temperature||0 ° C||10 ° C||20 ° C||30 ° C||40 ° C||50 ° C||60 ° C||70 ° C||80 ° C|
If the supply of moisture from the ambient air is sufficiently large, the entire sediment can be consumed. The relative equilibrium humidity above a saturated solution is therefore also the deliquescence humidity at the relevant temperature: A sodium chloride crystal dissolves in air with a relative humidity above about 75%.
With a content of 23.4% sodium chloride in aqueous solution, it forms a eutectic mixture . This solidifies at the eutectic point of −21.3 ° C homogeneously and without segregation. This solution is called a cryohydrate . Below 0.15 ° C a stable dihydrate NaCl · 2H 2 O is formed. The salt dissolves very well in aqueous ammonia solution . At lower temperatures, a pentaammonia solvate NaCl · 5NH 3 can precipitate in the form of colorless needles. Addition compounds with urea , glucose and sucrose are also known.
The aqueous solution and the melt conduct electrical current due to the (electrolytic or thermal) dissociation of sodium chloride into its ions . The conductivity of the melt increases with temperature. In contrast, pure crystalline sodium chloride is practically non-conductive.
Temperature dependence of the electrical conductivity of the sodium chloride melt temperature in ° C 800 850 900 1000 1100 Electrical conductivity σ in S m −1 3.58 3.75 3.90 4.17 4.39
The standard enthalpies of formation and entropies are given in the following table.
Compilation of the most important thermodynamic properties property Type Value [unit] Remarks Standard enthalpy of formation Δ f H 0 solid
Δ f H 0 liquid
Δ f H 0 gas
−411.12 kJ mol −1
−385.92 kJ mol −1
−181.42 kJ mol −1
as a solid
as a liquid
as a gas, 1 bar
entropy S 0 solid
S 0 liquid
S 0 gas
72.11 J mol −1 K −1
95.06 kJ mol −1
229.79 kJ mol −1
as a solid
as a liquid
as a gas, 1 bar
Specific heat capacity c p 0.85 J g −1 K −1 at 25 ° C Enthalpy of fusion Δ f H 520 J g −1 at the melting point
As table salt, sodium chloride is an important part of the human diet. It is used to flavor almost all dishes. Since the time of industrialization, however, industrial use has played a far greater role in terms of quantity. Different additives are mixed in depending on the application.
Depending on the use, a distinction is made between industrial salt as a raw material for the chemical industry, de-icing salt for road maintenance in winter, commercial salt for a wide variety of industrial and commercial purposes and table salt for human consumption. The proportions of these uses for Germany and the USA are given in the following table:
|Industrial salt||De-icing salt||Industrial salt||salt||unknown|
|USA (2007)||39%||37%||12% *||3%||9%|
* further differentiated into 7% (non-chemical) industrial, 3% agricultural use and 2% regeneration salt
Only the sodium chloride used in the basic chemical industry is referred to as industrial salt. It is rock salt, with appropriate local market conditions, such as in India, also sea salt and, to a large extent, brine, some of which is transported in pipelines. For the USA, the proportion of brine is given as 90%. It is a versatile raw material in the chemical industry and the basis for many products, whereby the production of important raw materials essentially begins with two different processes:
- Chloralkali electrolysis with the products hydrogen , chlorine and caustic soda , which are further processed on the one hand by chlorine chemistry and on the other hand by using sodium hydroxide .
- Solvay process with the products sodium carbonate (soda) and sodium hydrogen carbonate (baking soda). Soda is u. a. required for the melting of quartz sand as a raw glass material and for the production of dyes and detergents and cleaning agents. Soda is used as baking powder and fire extinguishing powder, for medicines and as a feed additive.
Other important secondary products are plastics, medicinal preparations and pesticides.
Rock salt is used as de-icing salt (road salt ) in winter at moderate freezing temperatures , sometimes with additives to maintain the flowability. In Germany, de-icing salt was colored to prevent its use in the preparation of food. With the abolition of the salt tax on January 1, 1993, this became obsolete. Before spreading, brine is also added to produce more suitable moist salt.
Practically all salt used commercially, technically or industrially that does not fall into one of the other three categories is referred to as industrial salt. Salt for the purpose of food preservation counts as industrial salt, although it is consumed in small quantities. The spectrum of industrial salt is therefore very large and ranges from coarse, unpurified rock salt to high-purity sodium chloride and sterile preparations for chemical, pharmaceutical and medical purposes. A wide variety of additives are also added depending on the use.
Cattle salt is added to the feed of farm animals such as cattle, sheep and goats (unpurified, denatured rock salt, possibly with other mineral salts as additives). This increases their appetite and contributes to overall health.
Salt is traditionally used to preserve food such as meat ( salted herring ), fish (such as salted herring ), vegetables ( sauerkraut ), etc. The osmotic effect of the salt removes moisture from the property. This removes the basis of water for harmful organisms, but also kills germs and pathogens.
Nitrite curing salt consists of a mixture of table salt and sodium nitrate, sodium nitrite or potassium nitrate.
Cheese is prepared in salted water before it is ripened, and brined with brine during the ripening process to keep the crust dry.
Physical / chemical applications
Also in the leather processing and dyeing salt is a vital commodity.
In the manufacture of dishes and other ceramics , the traditional salt glaze is created by adding moist salt at a high temperature . The sodium ion of the table salt dissociated in the furnace atmosphere combines with the silicates of the clay to form a permanent glaze. However, the salt is aggressive at the application temperatures (1,200 ° C and higher) and damages the inside of the furnace (the heat insulation on the fire side), which therefore has to be replaced more often.
The ionizing effect of the salt is used in metal processing .
In modern medicine, a 0.9% solution of sodium chloride in water is administered intravenously to replenish the blood volume ( isotonic saline solution , also called physiological saline solution) after severe blood loss, for example during an operation or an accident . It is iso-osmotic with the blood plasma. Furthermore, NaCl solution is used to keep vein accesses open and as a carrier solution for drugs.
In ancient times and in the Middle Ages, salt-based drugs were considered effective remedies. The skin of newborns was rubbed with salt to strengthen them. It was used in wound dressings, plasters, ointments, powders, and baths. Particular importance was attached to the drying and warming effects of the salt.
In the Middle Ages, salt was also used for the external treatment of ulcers and wounds, as it was considered astringent , cleansing and soothing.
Salt was sprinkled in wounds to prevent inflammation - a sometimes very painful procedure that has found its way into the German language in a corresponding phrase ("sprinkle salt in open wounds"). Pure salt destroys all cells via osmosis - including pathogenic microorganisms such as bacteria and fungi, but also the cells of the wounded person. This type of disinfection is therefore double-edged, as is the practice of burning out wounds. The same mechanism of action prevented food preserved in table salt from spoiling - i.e. being broken down by microorganisms.
Salt baths are still used today as a remedy. Spa stays by the sea or in salty air near salt pans and earlier also in salt mines are used to treat respiratory diseases. Where this is not possible or too expensive, inhalation devices are used in which salt aerosol is inhaled.
Crystalline sodium chloride is sufficiently transparent to light with wavelengths between 0.21 and 25 µm to be used for optical elements. Lenses, prisms and windows that are suitable for the visible range as well as in the near to mid- infrared are therefore made from sodium chloride . Due to the water solubility of sodium chloride, optical elements made from this material are damaged by humidity. However, this can be prevented if their temperature is kept above the ambient temperature. For this reason, heaters are often integrated in the brackets used. Sodium chloride windows are often used as Brewster windows for powerful, pulsed CO 2 lasers , but also in other areas. In infrared spectroscopy , it is pressed into tablets as a carrier for test samples.
Table salt is essential for human life (see physiological significance ). Table salt used to be very valuable. The preparation of meals is simplified and the taste is improved by the function as a spice . The lethal dose that leads to hypernatremia is given as 0.5 to 5 grams per kilogram of body weight in adults.
Today the commercially available salt is often iodized, i.e. mixed with food-safe iodine compounds and is supposed to prevent possible iodine deficiency . In the trade it is called iodized salt . In addition, table salt crystals are usually coated with a release agent to maintain the flowability .
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- by Martin Bertau, Armin Müller, Peter Fröhlich, Michael Katzberg, Karl Heinz Büchel, Hans-Heinrich Moretto, Dietmar Werner: Industrial Inorganic Chemistry - Martin Bertau, Armin Müller, Peter Fröhlich, Michael Katzberg, Karl Heinz Büchel, Hans-Heinrich Moretto , Dietmar Werner . John Wiley & Sons, 2013, ISBN 978-3-527-64958-7 ( limited preview in Google Book Search).
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- United States Geological Survey: Salt World Production and Reserves
- Kseniya A. Tikhomirova, Christian Tantardini, Ekaterina V. Sukhanova, Zakhar I. Popov, Stanislav A. Evlashin *, Mikhail A. Tarkhov, Vladislav L. Zhdanov, Alexander A. Dudin, Artem R. Oganov, Dmitry G. Kvashnin, Alexander G. Kvashnin: Exotic Two-Dimensional Structure: The First Case of Hexagonal NaCl in J. Phys. Chem. Lett. 11 (2020) 3821-3827, doi : 10.1021 / acs.jpclett.0c00874 .
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- see meereisportal.de - phase diagram of sea ice
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