Sodium Chloride
Sodium Chloride
Sodium chloride (chemical formula NaCl), known as table salt, rock salt, sea salt, and the mineral halite, is an ionic compound consisting of cube-shaped crystals composed of the elements sodium and chlorine. It is responsible for the saltiness of the world’s oceans. This salt has been of importance since ancient times and has a large and diverse range of uses. One of its largest uses is as an ingredient of salt that humans use in the eating and preparing of foods. It can be prepared chemically and is obtained by mining and evaporating water from seawater and brines.
Properties
Sodium chloride is colorless in its pure form. It is somewhat hygroscopic, or absorbs water from the atmosphere. The salt easily dissolves in water. Its dissolution in water is endothermic, which means it takes some heat energy away from the water. Sodium chloride melts at 1,474°F(801°C), boils at 2,670°F(1,465°C), has a density of 2.16 g/cm3 (at 25°C), and conducts electricity when dissolved or in the molten state.
Bonds
An ionic compound such as sodium chloride is held together by an ionic bond. This type of bond is formed when oppositely charged ions attract. This attraction is similar to that of two opposite poles of a magnet. An ion or charged atom is formed when the atom gains or loses one or more electrons. It is called a cation if a positive charge exists and an anion if a negative charge exists.
Sodium (chemical symbol Na) is an alkali metal and tends to lose an electron to form the positive sodium ion (Na+). Chlorine (chemical symbol Cl) is a nonmetal and tends to gain an electron to form the negative chloride ion (Cl-).
The oppositely charged ions Na+ and Cl- attract to form an ionic bond. Many sodium and chloride ions are held together this way, resulting in a salt with a distinctive crystal shape. The three-dimensional arrangement or crystal lattice of ions in sodium chloride is such that each Na+ is surrounded by six anions (Cl-) and each Clis surrounded by six cations (Na+). Thus the ionic compound has a balance of oppositely charged ions and the total positive and negative charges are equal.
Location and processing
Sodium chloride, found abundantly in nature, occurs in seawater, other saline waters or brines, and in dry rock salt deposits. It can be obtained by mining and evaporating water from brines and seawater. This salt can also be prepared chemically by reacting hydrochloric acid (chemical formula HCl) with sodium hydroxide (chemical formula NaOH) to form sodium chloride and water. Countries leading in the production of salt include the United States, China, Mexico, and Canada.
Mining
Two ways of removing salt from the ground are room and pillar mining and solution mining. In the room and pillar method, shafts are sunk into the ground and miners use techniques such as drilling and blasting to break up the rock salt. The salt is removed in such a way that empty rooms remain that are supported by pillars of salt.
In solution mining, water is added to the salt deposit to form brine. Brine is a solution of sodium chloride and water that may or may not contain other salts. In one technique, a well is drilled in the ground and two pipes (a smaller pipe placed inside a larger one) are placed in it. Fresh water is pumped through the inner pipe to the salt. The dissolved salt forms brine which is pumped through the outer pipe to the surface and then removed.
Evaporation
A common way to produce salt from brine is by evaporating the water using vacuum pans. In this method brine is boiled and agitated in huge tanks called vacuum pans. High quality salt cubes form and settle to the bottom of the pans. The cubes are then collected, dried, and processed.
Solar evaporation of seawater to obtain salt is an old method that is widely used today. It uses the sun as a source of energy. This method is successful in places that have abundant sources of salt water, land for evaporating ponds, and hot, dry climates to enhance evaporation. Seawater is passed through a series of evaporating ponds. Minerals contained in the seawater precipitate or drop out of solution at different rates. Most of them precipitate before sodium chloride and therefore are left behind as the seawater is moved from one evaporating pond to another.
Uses
Since ancient times, the salt sodium chloride has been of importance. It has been used in numerous ways including the flavoring and preserving of food and even as a form of money. This salt improves the flavor of food items such as breads and cheeses, and it is an important preservative in meat, dairy products, margarine, and other items, because it retards the growth of microorganisms. Salt promotes the natural development of color in ham and hot dogs and enhances the tenderness of cured meats like ham by causing them to absorb water. In the form of iodized salt, it is a carrier of iodine. (Iodine is necessary for the synthesis of thyroid hormones, which influence growth, development, and metabolic rates).
The chemical industry uses large amounts of sodium chloride salt to produce other chemicals. Chlorine and sodium hydroxide are electrolically produced from brine.
KEY TERMS
Brine —A solution of sodium chloride and water that may or may not contain other salts.
Ion —An atom or molecule that has acquired electrical charge by either losing electrons (positively charged ion) or gaining electrons (negatively charged ion).
Ionic bond —The attractive forces between positive and negative ions that exist when electrons have been transferred from one atom to another.
Ionic compound —A compound consisting of positive ions (usually, metal ions) and negative ions (nonmetal ions) held together by electrostatic attraction.
Solar evaporation —A method of water evaporation that uses the sun as a source of energy.
Chlorine products are used in metal cleaners, paper-bleach, plastics, and water treatment. The chemical soda ash, which contains sodium, is used to manufacture glass, soaps, paper, and water softeners. Chemicals produced as a result of sodium chloride reactions are used in ceramic glazes, metallurgy, curing of hides, and photography.
Sodium chloride has a large and diverse range of uses. It is spread over roads to melt ice by lowering the melting point of the ice. The salt has an important role in the regulation of body fluids. It is used in medicines and livestock feed. In addition, salt caverns are used to store chemicals such as petroleum and natural gas.
See also Food preservation; Saltwater.
Resources
BOOKS
Emsley, John. Nature’s Building Blocks: An A-Z Guide to the Elements. Oxford, UK: Oxford University Press, 2003.
Kurlansky, Mark. Salt: A World History. New York: Penguin Books, 2003.
Lide, David R., ed. CRC Handbook of Chemistry and Physics Boca Raton, FL: CRC Press, 2005.
Myers, R. Thomas, Keith B. Oldham, and Salvatore Tocci. Holt Chemistry Visualizing Matter. Austin, TX: Holt, Rinehart and Winston, 2000.
Siekierski, Slawomir. Concise Chemistry of the Elements. Chichester, UK: Horwood Publishing, 2002.
Snyder, C.H. The Extraordinary Chemistry of Ordinary Things. 4th ed. New York: John Wiley and Sons, 2002.
Dana M. Barry
Sodium Chloride
Sodium Chloride
OVERVIEW
Sodium chloride (SO-dee-um KLOR-ide) is a colorless to white powder or crystalline solid with no odor and a characteristic salty taste. It is slightly hygroscopic, meaning that it tends to absorb moisture from the air and become damp.
KEY FACTS
OTHER NAMES:
Salt; table salt; common salt; rock salt
FORMULA:
NaCl
ELEMENTS:
Sodium, chlorine
COMPOUND TYPE:
Binary salt (inorganic)
STATE:
Solid
MOLECULAR WEIGHT:
58.44 g/mol
MELTING POINT:
800.7°C (1473°F)
BOILING POINT:
1465°C (2669°F)
SOLUBILITY:
Soluble in water and glycerol; very slightly soluble in ethyl alcohol and methyl alcohol
Salt is probably one of the best known and most widely used of all chemical compounds. Humans have been using salt as a preservative and to flavor foods since the beginning of recorded time. One of the earliest mentions of sodium chloride dates to 2,700 BCE in the Chinese book Peng Tzao Kan Mu, probably the first book on pharmacology ever written. Access to salt resources has often been a contentious issue among peoples, leading to battles and wars over its ownership. It has been considered at times to be so valuable that it was used as a form of money. Today, sodium chloride has a host of applications beyond its use as a food additive.
HOW IT IS MADE
Sodium chloride occurs naturally as the mineral halite and abundantly in the oceans, where it is found in seawater at an average concentration of about 2.6 percent. There are several methods for harvesting salt, some of which date to ancient times. The earliest known method of production is also the simplest: evaporation of seawater by the Sun. In this method, seawater is collected in large, shallow ponds and allowed to evaporate. The salts dissolved in the water crystallize on the bottom of the ponds and can be scraped off and the individual compounds present-including sodium chloride-separated from each other.
This method works best in hot, arid parts of the world. In cooler, moister regions, seawater must be collected in large containers that can be heated artificially. In many cases, the seawater is heated under reduced pressure to allow it to boil at a lower temperature and save heating costs. Again, crystals of sodium chloride (and other dissolved salts) form as the water boils away.
Perhaps the most important source of sodium chloride is salt mines, large underground reserves of sodium chloride left behind when ancient seas dried up and were buried by the accumulation of rocks and soil. Salt mines are found in many parts of the world, especially Russia, Germany, the United Kingdom, India, France, Mexico, Canada, and the United States. These mines often span many kilometers and extend hundreds of meters deep. One of the most famous salt mines in the United States is located under the city of Detroit. It contains more than 80 kilometers (50 miles) of underground roads built to remove blocks of sodium chloride, some as wide as four-lane highways. The Detroit mine ceased production in 1983 when lower salt prices and resulting lower profits were no longer able to sustain the costs of extraction. The Detroit mine was reopened in 1988, but only for the mining of road salt.
Two methods of mining are used to remove sodium chloride from underground sources. In the room-and-pillar method, shafts are dug into the deposit. Drilling and blasting are then used to break off pieces of sodium chloride, which are removed for processing. As mining progresses, large pillars of salt are left standing to support the empty chambers. Thus the name: room-and-pillar. A second method of salt removal is solution mining. A well is drilled into the ground and flooded to create a saturated solution of sodium chloride, a brine solution. The brine is then pumped to the surface and processed.
COMMON USES AND POTENTIAL HAZARDS
Probably the best known use of sodium chloride is as a food additive. The Salt Institute estimates that humans consume an average of 16 tons of salt during their lifetimes. Salt has long been used on foods to improve flavor and also as a preservative. Salted foods last longer than unsalted foods because salt inhibits the growth of microorganisms that cause decay.
Still, the most important use of sodium chloride by far is as a raw material in the production of other compounds. In 2004, 65 percent of all the sodium chloride consumed in the United States was used in the production of sodium hydroxide, sodium carbonate, hydrogen chloride, sodium metal, chlorine gas, and other chemical products. The next most important use of sodium chloride is in water conditioners. The compound is used in such devices because the sodium in sodium chloride will replace the calcium and magnesium in "hard' water (water in which it is hard to make suds). By softening water with sodium chloride, clothing and other materials can be cleaned more efficiently at lower cost. The Salt Institute claims that sodium chloride has more than 14,000 distinct uses. Some of the most important of those uses include:
- As a feed additive for livestock, poultry, and other domestic animals, to ensure that they receive the sodium and chlorine they need to remain healthy and grow normally;
- As a deicing product on roads and highways;
- In the manufacture of glazes used on ceramic products;
- For the curing of animal hides;
- In the dyeing and printing of fabrics;
- In the manufacture of soaps;
- As a herbicide, a chemical used to kill weeds; and
- As a fire extinguisher for certain types of fires (such as grease fires).
Interesting Facts
- Salt was a key ingredient in the solution used by ancient Egyptians in the preparation of mummies.
- The expression "not worth his salt" had its origin in the ancient Greek slave trade, in which people were bought and sold for measures of salt.
- The English word salary comes from the Latin term salarium argentums, which refers to a special salt ration given to Roman soldiers.
- Salt has frequently been subject to heavy taxation; the very high tax on salt in France during the middle eighteenth century contributed to the rise of the French revolution.
- Salt mines that are no longer in use are sometimes used to store natural gas and petroleum.
Given its widespread use, sodium chloride is obviously safe for consumption by most humans under normal conditions. As with any chemical compound, consumption of a large excess of sodium chloride can be harmful. The one health issue of greatest concern has to do with high blood pressure. Scientists have learned that the ingestion of large amounts of sodium can contribute to hypertension (high blood pressure), which in turn is associated with increased risk for heart attacks and stroke. The American Heart Association recommends that healthy American adults consume no more than 2,300 milligrams of sodium a day. That amount is equivalent to about a teaspoon of salt. For those considered at higher risk, people with high blood pressure, blacks, and middle-aged and older adults, the 2005 U.S. Department of Agriculture guidelines recommend no more than 1,500 milligrams of sodium per day. The problem with sodium chloride consumption is that most people have no idea how much salt they eat every day. Of course, they can keep track of the salt they add to the foods they prepare in their own homes. But most commercially prepared foods also have sodium chloride added to them. In some cases, the total amount of salt ingested from processed foods by the average American can be significant, easily exceeding the recommended daily average recommended by the American Heart Association. People can, therefore, be consuming dangerously high levels of sodium without being aware of that fact.
Words to Know
- PHARMACOLOGY
- The study of compounds used as drugs.
FOR FURTHER INFORMATION
"History of Salt." The Salt Institute. http://www.saltinstitute.org/38.html (accessed on November 8, 2005).
Kurlansky, Mark. Salt: A World History. New York: Walker, 2002.
"Salt." History for Kids. http://www.historyforkids.org/learn/food/salt.htm (accessed on November 8, 2005).
"Sodium Chloride." J. T. Baker. http://www.jtbaker.com/msds/englishhtml/S3338.htm (accessed on November 8, 2005).
'What You Always Wanted to Know about Salt.' The Salt Institute. http://www.saltinstitute.org/4.html (accessed on November 8, 2005).
See AlsoChlorine; Sodium Hydroxide
Sodium Chloride
Sodium chloride
Sodium chloride (chemical formula NaCl), known as table salt , rock salt, sea salt and the mineral halite, is an ionic compound consisting of cube-shaped crystals composed of the elements sodium and chlorine . This salt has been of importance since ancient times and has a large and diverse range of uses. It can be prepared chemically and is obtained by mining and evaporating water from seawater and brines.
Properties
Sodium chloride is colorless in its pure form. It is somewhat hygroscopic, or absorbs water from the atmosphere. The salt easily dissolves in water. Its dissolution in water is endothermic , which means it takes some heat energy away from the water. Sodium chloride melts at 1,474°F (801°C), and it conducts electricity when dissolved or in the molten state.
Bonds
An ionic compound such as sodium chloride is held together by an ionic bond. This type of bond is formed when oppositely charged ions attract. This attraction is similar to that of two opposite poles of a magnet. An ion or charged atom is formed when the atom gains or loses one or more electrons. It is called a cation if a positive charge exists and an anion if a negative charge exists.
Sodium (chemical symbol Na) is an alkali metal and tends to lose an electron to form the positive sodium ion (Na+). Chlorine (chemical symbol Cl) is a nonmetal and tends to gain an electron to form the negative chloride ion (Cl-).
The oppositely charged ions Na+ and Cl- attract to form an ionic bond. Many sodium and chloride ions are held together this way, resulting in a salt with a distinctive crystal shape. The three-dimensional arrangement or crystal lattice of ions in sodium chloride is such that each Na+ is surrounded by six anions (Cl-) and each Cl-is surrounded by six cations (Na+). Thus the ionic compound has a balance of oppositely charged ions and the total positive and negative charges are equal.
Location and processing
Sodium chloride, found abundantly in nature, occurs in seawater, other saline waters or brines, and in dry rock salt deposits. It can be obtained by mining and evaporating water from brines and seawater. This salt can also be prepared chemically by reacting hydrochloric acid (chemical formula HCl) with sodium hydroxide (chemical formula NaOH) to form sodium chloride and water. Countries leading in the production of salt include the United States, China, Mexico and Canada.
Mining
Two ways of removing salt from the ground are room and pillar mining and solution mining. In the room and pillar method, shafts are sunk into the ground and miners use techniques such as drilling and blasting to break up the rock salt. The salt is removed in such a way that empty rooms remain that are supported by pillars of salt.
In solution mining, water is added to the salt deposit to form brine. Brine is a solution of sodium chloride and water that may or may not contain other salts. In one technique, a well is drilled in the ground and two pipes (a smaller pipe placed inside a larger one) are placed in it. Fresh water is pumped through the inner pipe to the salt. The dissolved salt forms brine which is pumped through the outer pipe to the surface and then removed.
Evaporation
A common way to produce salt from brine is by evaporating the water using vacuum pans. In this method brine is boiled and agitated in huge tanks called vacuum pans. High quality salt cubes form and settle to the bottom of the pans. The cubes are then collected, dried and processed.
Solar evaporation of seawater to obtain salt is an old method that is widely used today. It uses the Sun as a source of energy. This method is successful in places that have abundant sources of salt water, land for evaporating ponds, and hot, dry climates to enhance evaporation. Seawater is passed through a series of evaporating ponds. Minerals contained in the seawater precipitate, or drop out of solution at different rates. Most of them precipitate before sodium chloride and therefore are left behind as the seawater is moved from one evaporating pond to another.
Uses
Since ancient times, the salt sodium chloride has been of importance. It has been used in numerous ways including the flavoring and preserving of food and even as a form of money. This salt improves the flavor of food items such as breads and cheeses, and it is an important preservative in meat, dairy products, margarine and other items, because it retards the growth of microorganisms . Salt promotes the natural development of color in ham and hot dogs and enhances the tenderness of cured meats like ham by causing them to absorb water. In the form of iodized salt, it is a carrier of iodine. (Iodine is necessary for the synthesis of our thyroid hormones which influence growth, development and metabolic rates).
The chemical industry uses large amounts of sodium chloride salt to produce other chemicals. Chlorine and sodium hydroxide are electrolically produced from brine. Chlorine products are used in metal cleaners, paper bleach , plastics and water treatment . The chemical soda ash, which contains sodium, is used to manufacture glass , soaps, paper, and water softeners. Chemicals produced as a result of sodium chloride reactions are used in ceramic glazes, metallurgy , curing of hides, and photography .
Sodium chloride has a large and diverse range of uses. It is spread over roads to melt ice by lowering the melting point of the ice. The salt has an important role in the regulation of body fluids. It is used in medicines and livestock feed. In addition, salt caverns are used to store chemicals such as petroleum and natural gas .
See also Food preservation; Saltwater.
Resources
books
Emsley, John. The Consumer's Good Chemical Guide. New York: W.H. Freeman & Spektrum, 1994.
Hazen, Robert and Trefil, James. Science Matters. New York: Doubleday, 1991.
Lide, D.R., ed. CRC Handbook of Chemistry and Physics. Boca Raton: CRC Press, 2001.
Snyder, C.H. The Extraordinary Chemistry of Ordinary Things. 4th ed. New York: John Wiley and Sons, 2002.
Tocci, Salvatore and Viehland, Claudia. Chemistry Visualizing Matter. New York: Holt, Rinehart and Winston.
Dana M. Barry
KEY TERMS
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .- Brine
—A solution of sodium chloride and water that may or may not contain other salts.
- Ion
—An atom or molecule which has acquired electrical charge by either losing electrons (positively charged ion) or gaining electrons (negatively charged ion).
- Ionic bond
—The attractive forces between positive and negative ions that exist when electrons have been transferred from one atom to another.
- Ionic compound
—A compound consisting of positive ions (usually, metal ions) and negative ions (nonmetal ions) held together by electrostatic attraction.
- Solar evaporation
—A method of water evaporation that uses the sun as a source of energy.