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CAO

Calcium oxide
Calcium oxide
Calcium oxide powder.JPG
Names
IUPAC name
Calcium oxide
Other names
Quicklime, burnt lime, unslaked lime, pebble lime
Identifiers
3D model (Jmol)
ChEBI
ChemSpider
ECHA InfoCard 100.013.763
E number E529 (acidity regulators, ...)
485425
PubChem CID
RTECS number EW3100000
UNII
UN number 1910
Properties
CaO
Molar mass 56.0774 g/mol
Appearance White to pale yellow/brown powder
Odor Odorless
Density 3.34 g/cm3
Melting point 2,613 °C (4,735 °F; 2,886 K)
Boiling point 2,850 °C (5,160 °F; 3,120 K) (100 hPa)
Reacts to form calcium hydroxide
Solubility in Methanol Insoluble (also in diethyl ether, n-octanol)
Acidity (pKa) 12.8
−15.0·10−6 cm3/mol
Structure
Cubic, cF8
Thermochemistry
40 J·mol−1·K−1
−635 kJ·mol−1
Pharmacology
QP53AX18 (WHO)
Hazards
Safety data sheet Hazard.com
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g., phosphorus Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point Non-flammable
US health exposure limits (NIOSH):
PEL (Permissible)
 TWA 5 mg/m3
REL (Recommended)
 TWA 2 mg/m3
IDLH (Immediate danger)
 25 mg/m3
Related compounds
Other anions
Calcium sulfide
Calcium hydroxide
Other cations
Beryllium oxide
Magnesium oxide
Strontium oxide
Barium oxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline, crystalline solid at room temperature. The broadly used term lime connotes calcium-containing inorganic materials, in which carbonates, oxides and hydroxides of calcium, silicon, magnesium, aluminium, and iron predominate. By contrast, quicklime specifically applies to the single chemical compound calcium oxide. Calcium oxide that survives processing without reacting in building products such as cement is called free lime.

Quicklime is relatively inexpensive. Both it and a chemical derivative (calcium hydroxide, of which quicklime is the base anhydride) are important commodity chemicals.

Calcium oxide is usually made by the thermal decomposition of materials, such as limestone or seashells, that contain calcium carbonate (CaCO3; mineral calcite) in a lime kiln. This is accomplished by heating the material to above 825 °C (1,517 °F), a process called calcination or lime-burning, to liberate a molecule of carbon dioxide (CO2), leaving quicklime.

The quicklime is not stable and, when cooled, will spontaneously react with CO2 from the air until, after enough time, it will be completely converted back to calcium carbonate unless slaked with water to set as lime plaster or lime mortar.

Annual worldwide production of quicklime is around 283 million tonnes. China is by far the world's largest producer, with a total of around 170 million tonnes per year. The United States is the next largest, with around 20 million tonnes per year.


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