Sodium chloride

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Sodium chloride, also known as common salt, table salt, or halite, is a chemical 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 main ingredient in edible salt, it is commonly used as a condiment and food preservative. In one gram of sodium chloride, there are approximately 0.3933 grams of sodium, and 0.6067 g of chlorine.

Salt is currently 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 2002, world production was estimated at 210 million metric tonnes, the top five producers being the United States (40.3 million tonnes), China (32.9), Germany (17.7), India (14.5), and Canada (12.3).^[1]

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. In most of Canada and the northern USA, large quantities of rock salt are used to help clear highways of ice during winter, although “Road Salt” loses its melting ability at temperatures below -15°C to -20°C (5°F to -4°F).

Salt is also the raw material used to produce chlorine which itself is required for the production of many modern materials including PVC and pesticides. 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

2NaCl + 2H₂O → Cl₂ + H₂ + 2NaOH

Sodium metal is produced commercially through the electrolysis of liquid sodium chloride. This is 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.

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 and can also be used to detach leeches that have attached themselves to feed. It has also been used to disinfect wounds. In medieval times salt would be rubbed into household surfaces as a cleansing agent.

• Edible salt
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