Click Buttons Info on the author of this site Go to the Home Page Go to the Contact page Read Site Updates and latest news Go to the Utility Download Page Go to the Web Links Page View or Sign my Guest Book


CHEMISTRY : Metal Cation Identification


Information on CALCIUM




  1. General Information

  2. Occurence Uses and Properties

  3. History of the Metal

  4. Compounds
  5. Back to Main Metal List




General Information


Calcium (Ca), chemical element, one of the alkaline-earth metals of main Group IIa of the periodic table. It is the most abundant metallic element in the human body and the fifth most abundant element in the Earth's crust.

Calcium is the fifth most abundant element in the Earth's crust, to which it contributes an estimated 3.64 percent; its cosmic abundance is estimated at 4.9 104 atoms (Si = 106 atoms). One of the most widely distributed elements, it occurs as carbonate (chalk, limestone, marble, calcite), sulfate (anhydrite, gypsum), fluoride (fluorite or fluorspar), and phosphate (apatite). It is also found in a large number of siliCATes and aluminosiliCATes, in salt deposits, and in natural waters, including the sea. Calcium carbonate deposits dissolve in water that contains carbon dioxide to form calcium bicarbonate, Ca(HCO3)2. This process frequently results in the formation of caves and may reverse to deposit limestone as stalactites and stalagmites. Calcium is essential to both plant and animal life. A large number of living organisms concentrate calcium in their shells or skeletons, and indeed in higher animals calcium is the most abundant inorganic element. Many important carbonate and phosphate deposits owe their origin to living organisms.

The metal is produced by thermal reduction of lime with aluminum under high vacuum and by electrolysis of fused calcium chloride.. It reacts with water and, upon heating, with oxygen, nitrogen, hydrogen, halogens, boron, sulfur, carbon, and phosphorus as well. Calcium's commercial appliCATions depend largely on these reactions. Although it compares favourably with sodium as a reducing agent, calcium is more expensive and less reactive than the latter. In many deoxidizing, reducing, degasifying, and alloying appliCATions, however, calcium often is preferred because of its lower volatility. Small percentages of calcium are used in many alloys for special purposes.



Occurrence, uses, and properties.


Extensively used by the ancients as the compound lime, the silvery, rather hard but lightweight metal itself was first isolated (1808) by Sir Humphry Davy after distilling mercury from an amalgam formed by electrolyzing a mixture of lime and mercuric oxide. His discovery showed lime to be an oxide of calcium.

Calcium does not occur naturally in the free state, but compounds of the element are widely distributed, constituting 8 percent of the Moon's crust and 3.64 percent of the Earth's crust. As calcite (calcium carbonate), it occurs in limestone, chalk, marble, dolomite, eggshells, pearls, coral, stalactites, stalagmites, and the shells of many marine animals. As calcium phosphate, it is the principal inorganic constituent of teeth and bones and occurs as the mineral apatite. Calcium is found in many other minerals, such as fluorite, aragonite, and gypsum, and in many feldspars and zeolites.

The human body is 2 percent calcium. The major source of calcium in the human diet is milk and milk products. Rickets occurs, especially in infants and children, when lack of vitamin D impairs the absorption of calcium from the gastrointestinal tract into the extracellular fluids (see calcium deficiency).

Formerly produced by electrolysis of anhydrous calcium chloride, pure calcium metal is now made commercially by heating lime with aluminum.

The metal itself is used as an alloying agent for aluminum, copper, lead, magnesium, and other base metals; as a deoxidizer for certain high-temperature alloys, and for nickel, steel, and tin bronzes; as a getter in electron tubes; as a reducing agent in the preparation of chromium, thorium, uranium, zirconium, and other metals from their oxides; and as a dehydrating agent for organic liquids. Alloyed with lead (0.04 percent calcium), it is employed as sheaths for telephone cables and as grids for storage batteries of the stationary type. Limelights, formerly used in stage lighting, emit a soft, very brilliant white light upon heating a block of calcium oxide to incandescence in an oxyhydrogen flame; hence, the expression "to be in the limelight."

Naturally occurring calcium consists of a mixture of six isotopes: calcium-40 (96.94 percent), calcium-44 (2.09 percent), calcium-42 (0.65 percent), and smaller proportions of calcium-48, calcium-43, and calcium-46. The metal reacts slowly with oxygen, water vapour, and nitrogen of the air to form a yellow coating of the oxide, hydroxide, and nitride. It burns in air or pure oxygen to form the oxide and reacts rapidly with warm water and more slowly with cold water to produce hydrogen.



History.
The earliest known alkaline earth was lime (Latin: calx), which is now known to be calcium oxide; it was used in ancient times in the composition of mortar.

Magnesium, calcium, strontium, and barium--elements derived from alkaline earths--were isolated as impure metals by Sir Humphry Davy in 1808 by means of the electrolytic method he had previously used for isolating the alkali metals potassium and sodium. The alkaline-earth metals were later produced by reduction of their salts with free alkali metals.



Chemical compounds


The sulfate (as uncalcined gypsum) is employed as a soil corrector. Calcined gypsum is used in making tile, wallboard, lath, and various plasters. Plaster of Paris, the hemihydrate, CaSO4 1/2 H2O, is produced by partial calcination at about 120 C; mixed with water, it forms a plastic mass that hydrates to a hard white plaster.

The dihydrogen sulfite, Ca(HSO3)2, is made by the action of sulfur dioxide on a slurry of Ca(OH)2. Its aqueous solution under pressure dissolves the lignin in wood to leave cellulose fibres and thus finds considerable appliCATion in the paper industry.

The phosphates are the principal minerals for the production of phosphate fertilizers and for a whole range of phosphorus compounds. The rock is usually treated with sulfuric acid to form Ca(H2PO4)2, which may be applied directly to the land. The fluoride, CaF2, is important to the production of hydrofluoric acid, which is made from CaF2 by the action of sulfuric acid.
    Reference: Encyclopędia Britannica, Inc. 1994-2000 ©


Back to Menu Page





Chemistry Section Links