Calcium oxide

Calcium oxide
Names
IUPAC name
Calcium oxide
Other names
Quicklime, burnt lime, unslaked lime, pebble lime, calcia
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.013.763
E number E529 (acidity regulators, ...)
485425
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[1]
Melting point 2,613 °C (4,735 °F; 2,886 K)[1]
Boiling point 2,850 °C (5,160 °F; 3,120 K) (100 hPa)[2]
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[3]
−635 kJ·mol−1[3]
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
0
3
2
Flash point Non-flammable [4]
US health exposure limits (NIOSH):
PEL (Permissible)
 TWA 5 mg/m3[4]
REL (Recommended)
 TWA 2 mg/m3[4]
IDLH (Immediate danger)
 25 mg/m3[4]
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.[5]

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

Preparation

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),[6] a process called calcination or lime-burning, to liberate a molecule of carbon dioxide (CO2), leaving quicklime.

CaCO3(s) → CaO(s) + CO2(g)

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.[7]

Approximately 1.8 t of limestone is required per 1.0 t of quicklime. Quicklime has a high affinity for water and is a more efficient desiccant than silica gel. The reaction of quicklime with water is associated with an increase in volume by a factor of at least 2.5.[8]

Usage

CaO (s) + H2O (l) ⇌ Ca(OH)2 (aq) (ΔHr = −63.7 kJ/mol of CaO)
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 litre of water combines with approximately 3.1 kilograms (6.8 lb) 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.

As a weapon

In 80 BC, the Roman general Sertorius deployed choking clouds of caustic lime powder to defeat the Characitani of Hispania, who had taken refuge in inaccessible caves. A similar dust was used in China to quell an armed peasant revolt in 178 AD, when lime chariots equipped with bellows blew limestone powder into the crowds.[14]

David Hume, 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.[15] Quicklime may have been used in medieval naval warfare - up to the use of "lime-mortars" to throw it at the enemy ships.[16]

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.[17]

Safety

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.[18]

References

  1. 1 2 Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). Boca Raton, FL: CRC Press. p. 4.55. ISBN 1439855110.
  2. ↑ Calciumoxid Archived 2013-12-30 at the Wayback Machine.. GESTIS database
  3. 1 2 Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A21. ISBN 0-618-94690-X.
  4. 1 2 3 4 "NIOSH Pocket Guide to Chemical Hazards #0093". National Institute for Occupational Safety and Health (NIOSH).
  5. ↑ "free lime". DictionaryOfConstruction.com.
  6. ↑ Merck Index of Chemicals and Drugs, 9th edition monograph 1650
  7. ↑ Miller, M. Michael (2007). "Lime". Minerals Yearbook (PDF). U.S. Geological Survey. p. 43.13.
  8. 1 2 3 4 5 6 Tony Oates (2007), "Lime and Limestone", Ullmann's Encyclopedia of Industrial Chemistry (7th ed.), Wiley, pp. 1–32, ISBN 3527306730, doi:10.1002/14356007.a15_317
  9. ↑ Collie, Robert L. "Solar heating system" U.S. Patent 3,955,554 issued May 11, 1976
  10. ↑ Gray, Theodore (September 2007). "Limelight in the Limelight". Popular Science: 84.
  11. ↑ Neolithic man: The first lumberjack?. Phys.org (August 9, 2012). Retrieved on 2013-01-22.
  12. ↑ Karkanas, P.; Stratouli, G. (2011). "Neolithic Lime Plastered Floors in Drakaina Cave, Kephalonia Island, Western Greece: Evidence of the Significance of the Site". The Annual of the British School at Athens. 103: 27. doi:10.1017/S006824540000006X.
  13. ↑ Connelly, Ashley Nicole (May 2012) Analysis and Interpretation of Neolithic Near Eastern Mortuary Rituals from a Community-Based Perspective. Baylor University Thesis, Texas
  14. ↑ Adrienne Mayor (2005), "Ancient Warfare and Toxicology", in Philip Wexler, Encyclopedia of Toxicology, 4 (2nd ed.), Elsevier, pp. 117–121, ISBN 0-12-745354-7
  15. ↑ David Hume (1756). History of England. I.
  16. ↑ Sayers W. The Use of Quicklime in Medieval Naval Warfare // The Mariner's Mirror. - Volume 92 (2006). - Issue 3. - PP. 262-269.
  17. ↑ Croddy, Eric (2002). Chemical and biological warfare: a comprehensive survey for the concerned citizen. Springer. p. 128. ISBN 0-387-95076-1.
  18. ↑ CaO MSDS. hazard.com
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