The Sodium chloride reference article from the English Wikipedia on 24-Jul-2004
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Sodium chloride

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Properties

General

Name Sodium chloride
Chemical formula NaCl
Appearance White or clear solid
CAS-number 7647-14-5

Physical

Formula weight 58.4 amu
Melting point 1074 K (801 °C)
Boiling point 1738 K (1465 °C)
Density 2.2 ×103 kg/m3
Crystal structure f.c.c.
Solubility 35.9 g in 100g water

Thermochemistry

ΔfH0gas -181.42 kJ/mol
ΔfH0liquid -385.92 kJ/mol
ΔfH0solid -411.12 kJ/mol
S0gas, 1 bar 229.79 J/mol·K
S0liquid, 1 bar 95.06 J/mol·K
S0solid 72.11 J/mol·K

Safety

Ingestion Dangerous in large quantities
Inhalation May cause irritation
Skin May cause irritation
Eyes May cause irritation
More info Hazardous Chemical Database
SI units were used where possible. Unless otherwise stated, standard conditions were used.

Disclaimer and references

Sodium chloride, also known as common salt, table salt, or halite, is a chemical compound with formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms. It is commonly used as a flavour enhancer and preservative for food.

Table of contents
1 Biological Importance
2 Salt throughout history
3 Production and use
4 Random facts
5 Exterrnal links

Biological Importance

Sodium chloride is important to life on earth. Most tissues and body fluids contain a varying amount of NaCl. Humans are unusual among primates in secreting large amounts of salt by sweating.

0.9% sodium chloride in water is called a physiological solution because it is isoosmotic with blood plasma. It is known medically as normal saline. Physiological solution is the mainstay of fluid replacement therapy that is widely used in medicine in prevention or treatment of dehydration.

Salt is an essential element to human existence because our bodies require salt to function properly. The concentration of sodium ions in the blood is directly related to the regulation of safe body-fluid levels. Also the movement of electric signals in our nervous system (known as signal transduction) is regulated by sodium ions.

Salt throughout history

There are 32 references to salt in the Bible, the most familiar probably being the story of Lot's wife, who was turned into a pillar of salt when she disobeyed the angels and looked back at the wicked city of Sodom.

Salt's preservative ability was also a foundation of civilization. It eliminated dependency on the seasonal availability of food and allowed travel over long distances. By the Middle Ages, caravans consisting of as many as 40,000 camels traversed 400 miles of the Sahara bearing salt, sometimes trading it for slaves.

Salt was once one of the most valuable commodities known to man. In the Roman Empire, salt was sometimes even used as a currency. Throughout much of history, it influenced the conduct of wars, the fiscal policies of governments, and even the inception of revolutions. Salt was taxed, from as far back as the 20th century BC in China. Merchants in 12th-century Timbuktu—the gateway to the Sahara Desert and the seat of scholars—valued salt as highly as books and gold. The Roman Republic and Empire controlled the price of salt, increasing it to raise money for wars, or lowering it to be sure that the poorest citizens could easily afford this important part of the diet.

The empire of Mali, in Africa, valued salt enough to buy it for its weight in gold; this trade led to the legends of the incredibly wealthy city of Timbuktu, and fueled inflation in Europe, which was exporting the salt.

In later times, for instance during the British colonial period, salt production and transport were controlled in India as a means of generating enormous tax revenues. This ultimately led to a march led by Mahatma Gandhi in 1930 in which thousands of Indians went to the sea to produce their own salt in protest of the British tax on salt.

Production and use

Nowadays, salt is produced by evaporation of seawater or brine from other sources, such as brine wells and salt lakes, and by mining rock salt.

While most people are familiar with the many uses of salt in cooking, they might be unaware that salt is used in a plethora of applications, from manufacturing pulp and paper to setting dyes in textiles and fabric, to producing soaps and detergents.

Flavour enhancer

Salt is commonly used as a flavour enhancer for food and has been identified as one of the basic tastes. Ironically, given its history, this has resulted in large sections of the developed world ingesting salt massively in excess of the required intake, particularly in colder climates where the required intake is much lower. This causes elevated levels of blood pressure in some, which in turn is associated with increased risks of heart attack and stroke.

Biological uses

Many microorganisms 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 has also been used to disinfect wounds.

Image:SaltMounds.jpeg

De-icing

While salt was a scarce commodity in history, industrialised production has now made salt plentiful. About 51% of world output is now used by northern countries to de-ice roads in winter. This works because salt water has a lower
freezing point than pure water: the ions prevent regular ice crystals from forming.

Additives

The salt we buy for consumption today are not purely sodium chloride as most people assume. In 1911 Magnesium carbonate was first added to salt to make it flow more freely. In 1924 trace amounts of iodine were first added, creating iodized salt to reduce the incidence of simple goiter.

Etymology

Salt has also had influence on our language. Many of its effects can still be seen today. Words and expressions related to salt mostly come from the Roman and Greek civilizations when salt was still a valuable commondity.

The Latin word for salt, "sal," the French words "solde" (meaning pay) and "soldier", are all related. In Italian "soldi" means money, "soldato" is a soldier.

Roman soldiers were given a particular allowance to purchase salt (Latin: sal), salarium argentum, from which we take our English word "salary". The Romans also preferred salting of their greens, which led to the Latin word for salt being integrated in our word "salad".

Also the expression "He is not worth his salt" can be traced back to ancient Greece where salt was traded for slaves.

Random facts

Exterrnal links

See also : Salt, Black salt, soap, Sodium