Calcium oxide

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Calcium oxide
CAS number 1305-78-8 YesY
PubChem 14778
ChemSpider 14095
UN number 1910
RTECS number EW3100000
ATCvet code QP53AX18
Jmol-3D images Image 1
Molecular formula CaO
Molar mass 56.077 g/mol
Appearance White to pale yellow powder
Density 3.35 g/cm3
Melting point

2572 °C (2845 K)

Boiling point

2850 °C (3123 K)

Solubility in water reacts
Solubility in [[acids, glycerol, sugar solution]] soluble
Solubility in [[methanol, diethyl ether, n-octanol]] insoluble
Acidity (pKa) 12.5
MSDS [1]
EU Index Not listed
NFPA 704
NFPA 704.svg
Flash point Non-flammable
Related compounds
Other anions Calcium sulfide
Calcium hydroxide
Other cations Beryllium oxide
Magnesium oxide
Strontium oxide
Barium oxide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 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, aluminum, & iron predominate, such as limestone. By contrast, quicklime specifically applies to a single chemical compound.

Calcium oxide is usually made by the thermal decomposition of materials such as limestone, that contain calcium carbonate (CaCO3; mineral calcite) in a lime kiln. This is accomplished by heating the material to above 825 °C,[1] 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 is completely converted back to calcium carbonate.


[edit] Usage

Quicklime is relatively inexpensive. Both it and a chemical derivative (calcium hydroxide) are important commodity chemicals.

Quicklime produces heat energy by the formation of the hydrate, calcium hydroxide, by the following equation:[2]

CaO (s) + H2O (l) is in equilibrium with Ca(OH)2 (aq) (ΔHr = −63.7 kJ/mol of CaO)

The product, commonly called "slaked lime", has many uses on its own. As it hydrates, an exothermic reaction results and the solid puffs up. The hydrate can be reconverted to quicklime by removing the water by heating it to redness to reverse the hydration reaction. One liter of water combines with approximately 3.1 kg of quicklime to give calcium hydroxide plus 3.54 MJ of energy. This process can be used to provide a convenient portable source of heat, as for on-the-spot food warming in a self-heating can.

When quicklime is heated to 2400 °C (4300 °F), it emits an intense glow. This form of illumination is known as a limelight, and was used broadly in theatrical productions prior to the invention of electric lighting.[3]

Precipitated calcium carbonate, made by dropping calcium oxide into water, is used by itself or with additives as a white paint, known as whitewashing.

Annual worldwide production of quicklime is around 283 million metric tons. China is by far the world's largest producer, with a total of around 170 million metric tons per year. The United States is the next largest with around 20 million metric tons per year.[4]

[edit] Use as a weapon

Historian and philosopher David Hume of Godscroft, in his history of England, recounts that early in the reign of Henry III, the English Navy destroyed an invading French fleet by blinding the enemy fleet with quicklime:

D’Albiney employed a stratagem against them, which is said to have contributed to the victory: Having gained the wind of the French, he came down upon them with violence; and throwing in their faces a great quantity of quick lime, which he purposely carried on board, he so blinded them, that they were disabled from defending themselves.[5]

Quicklime is also thought to have been a component of Greek fire. Upon contact with water, quicklime would increase its temperature above 150 °C and ignite the fuel.[6]

[edit] Health issues

Because of vigorous reaction of quicklime with water, quicklime causes severe irritation when inhaled or placed in contact with moist skin or eyes. Inhalation may cause coughing, sneezing, labored breathing. It may then evolve into burns with perforation of the nasal septum, abdominal pain, nausea and vomiting. Although quicklime is not considered a fire hazard, its reaction with water can release enough heat to ignite combustible materials.[7]

[edit] References

  1. ^ Merck Index of chemicals and Drugs , 9th edition monograph 1650
  2. ^ U.S. Patent 3,955,554, Solar heating system.
  3. ^ Gray, Theodore (September 2007). "Limelight in the Limelight". Popular Science: 84. 
  4. ^ Miller, M. Michael (2007). "Lime". Minerals Yearbook. U.S. Geological Survey. p. 43.13. 
  5. ^ David Hume (1688). History of England. I. 
  6. ^ Croddy, Eric (2002). Chemical and biological warfare: a comprehensive survey for the concerned citizen. Springer. p. 128. ISBN 0387950761. 
  7. ^ CaO MSDS

[edit] External links

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