Calcium Carbonate | Research & Encyclopedia Articles

Calcium Carbonate

Overview

Calcium carbonate (KAL-see-um CAR-bun-ate) is one of the most common compounds on Earth, making up about 7 percent of Earth's crust. It occurs in a number of minerals and other natural materials, including aragonite, calcite, chalk, limestone, marble, marl, oyster shells, pearls, and travertine. Stalactites and stalagmites found in caves are made primarily of calcium carbonate. As indicated by the melting points of aragonite and calcite, the compound's physical properties may differ somewhat depending on its crystal form. It typically occurs as an odorless, tasteless white powder or colorless crystals.

Key Facts

Other Names:

Limestone; chalk; aragonite; calcite

Formula:

CaCO₃

Elements:

Calcium, carbon, oxygen

Compound Type:

Inorganic salt

State:

Solid

Molecular Weight:

100.09 g/mol

Melting Point:

Calcite: 1330°C (2430°F); aragonite: decomposes at about 825°C (1520°F)

Boiling Point:

Not applicable

Solubility:

Very slightly soluble in water; soluble in dilute acids; insoluble in organic solvents

How It Is Made

Calcium carbonate is so abundant in nature that demand for the compound can be met by mining natural sources, such as chalk, limestone, and marble quarries. The compound can also be produced in the laboratory by reacting calcium chloride (CaCl₂) with sodium carbonate (Na₂CO₃). The calcium carbonate formed in this reaction precipitates out of (separates from) the solution and can be recovered by filtration.

Common Uses and Potential Hazards

One well known use of calcium carbonate is as an antacid, a substance that neutralizes excess stomach acid (hydrochloric acid; HCl) and relieves the symptoms of acid indigestion, heartburn, upset stomach, and sour stomach. Large amounts of the chemical are also used for a variety of industrial uses, including:

• In agriculture, where it is used to maintain proper acidity of soil and supply calcium needed by growing plants;

Interesting Facts

• It is said that Cleopatra showed her extravagance by dissolving pearls (which are made of calcium carbonate) in vinegar and drinking the resulting solution.
• Stalagmites and stalactites form in caves when calcium bicarbonate (CaHCO₃) dissolved in groundwater reaches the top of a cave and gives up carbon dioxide (CO₂) to the air. When calcium bicarbonate loses carbon dioxide, it is converted to calcium carbonate, which precipitates out on the roof of the cave as a stalactite. If the calcium bicarbonate does not lose carbon dioxide until it drips off the roof and falls on the floor of the cave, the calcium carbonate that is formed builds up a stalagmite on the floor of the cave.

• In the paper-making industry, where it is used to make strong products with a very white color, glossy finish, and firm texture for printing and dyeing;
• As a filler in the manufacture of plastics to reduce the cost of production;
• In the construction industry, where it is used in the production of concrete structures, such as paving-stones, tubes, and sewage tanks, in ready-mixed concrete, and in prefabricated elements;
• In the production of paints and other types of coating materials because of its ability to provide weather resistance, protect the coating against corrosion, reduce drying time, and maintain the proper acidity of the coating material;
• In a variety of environmental applications, such as counteracting the increased acidity of lakes and other bodies of water caused by acid precipitation, treating waste gases to remove sulfur and nitrogen oxides that pollute the air; and purifying water and waste water; and
• In the manufacture of lime (calcium oxide; CaO) which, itself, has a host of industrial applications.

Words to Know

PRECIPITATE

A solid material that settles out of a solution, often as the result of a chemical reaction.

For Further Information

"Calcium Carbonate." National Institute for Occupational Safety and Health. http://www.cdc.gov/niosh/npg/npgd0090.html (accessed on September 24, 2005).

"Calcium Carbonate Powder." Reade. http://www.reade.com/Products/Minerals_and_Ores/calcium_carbonate.html (accessed on September 24, 2005).

Tegethoff, F. Wolfgana, with Johannes Rohleder and Evelyn Kroker, eds. Calcium carbonate: From the Cretaceous period into the 21st century. Boston: Birkhäuser Verlag, 2001.

See Also

Calcium Oxide