Calcium carbide

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Calcium carbide
Image:Cac2.jpg
General
Systematic name	Calcium Carbide
Other names
Molecular formula	CaC₂
Molar mass	64.1 g/mol
Appearance	gray-black Crystals
Crystal Structure	orthorhombic
CAS number	75-20-7
Properties
Density and phase	2.22 g/cm³
Melting point	2300 °C
Boiling point
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Calcium carbide is a chemical compound with the chemical formula Ca C₂. It has the appearance of grayish white lumps.

Calcium carbide is produced in an electric arc furnace loaded with a mixture of lime and coke at about 2000 °C under the equation CaO + 3C→CaC₂ + CO. The compound reacts vigorously with water to form acetylene. This reaction is the basis of the industrial manufacture of dissolved acetylene (DA), and is one of the modern industrial uses for calcium carbide. Calcium carbide is also used as a fuel in steelmaking to extend the scrap ratio to liquid iron depending on economics. It is also used as a powerful deoxidizer at ladle treatment facilities.

Calcium carbide is used in carbide lamps, in which water drips on carbide and the formed acetylene is ignited. The lamps found extensive use in coal mines, but most have now been replaced by electric lamps. Carbide lamps are still used by some cavers exploring caves and other underground areas. They were also used extensively as head lights in early automobiles, though in this application they are also obsolete, having been replaced entirely by electric lamps.

It is still used in the Netherlands and Belgium for a traditional custom called Carbidschieten (Shooting Carbide), and in toy cannons.

The reaction of calcium carbide with water was discovered by Friedrich Wohler in 1862. The equation is:

CaC₂ + 2 H₂O → C₂H₂ + Ca(OH)₂

Therefore, 1 gram of CaC₂ gives 349ml of acetylene.

Together with calcium phosphide, calcium carbide is used in floating, self-igniting naval signal flares (see Holmes' Marine Life Protection Association).

Calcium carbide is also used in small carbide lamps called carbide candles, which are used for blackening rifle sights to reduce glare. These "candles" are used due to the sooty flame produced by acetylene.

[edit] Industrial history

Calcium carbide synthesis requires an extremely high temperature, ~2000 °C, which is not practically achievable by traditional combustion, so the reaction is performed in an electric arc furnace with graphite electrodes. This reaction was an important part of the industrial revolution in chemistry that occurred as a product of massive amounts of cheap hydro-electric power liberated from Niagara Falls before the turn of the 19th century.