Calcium oxide
IUPAC name Calcium oxide
Other names Quicklime, Burnt lime, Unslaked lime
Identifiers
CAS number	1305-78-8 Y
PubChem	14778
ChemSpider	14095
UNII	C7X2M0VVNH
UN number	1910
RTECS number	EW3100000
ATCvet code	QP53AX18
Jmol-3D images	Image 1
SMILES [Ca]=O
InChI InChI=1/Ca.O/rCaO/c1-2 Key: ODINCKMPIJJUCX-BFMVISLHAU
Properties
Molecular formula	CaO
Molar mass	56.0774 g/mol
Appearance	White to pale yellow/brown powder
Odor	odorless
Density	3.35 g/cm3
Melting point	2572 °C, 2845 K, 4662 °F
Boiling point	2850 °C, 3123 K, 5162 °F
Solubility in water	1.19 g/L (25 °C), 0.57 g/L (100 °C), exothermic reaction[1]
Solubility in acids	soluble (also in glycerol, sugar solution)
Solubility in methanol	insoluble (also in diethyl ether, n-octanol)
Acidity (pKa)	12.8
Thermochemistry
Std enthalpy of formation ΔfHo298	−635 kJ·mol−1[2]
Standard molar entropy So298	40 J·mol−1·K−1[2]
Hazards
MSDS	[1]
EU Index	Not listed
NFPA 704	0 3 2
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, aluminium, and iron predominate, such as limestone. By contrast, quicklime specifically applies to a single chemical compound.

Preparation[link]

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 (1,517 °F),^[3] 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.

Usage[link]

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:^[4]

CaO (s) + H₂O (l) Ca(OH)₂ (aq) (ΔH_r = −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.

When quicklime is heated to 2,400 °C (4,350 °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.^[5]

Precipitated calcium carbonate is made by mixing calcium oxide into water, and then bubbling carbon dioxide into the solution. It is used by itself or with additives as a white paint, known as whitewashing.

Calcium oxide is also a key ingredient for the process of making both cement and Pulp (paper).

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.^[6]

Use as a weapon[link]

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.^[7]

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.^[8]

Health issues[link]

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.^[9]

References[link]

External links[link]

• Lime Statistics & Information from the United States Geological Survey
• Factors Affecting the Quality of Quicklime
• American Scientist (discussion of ¹⁴C dating of mortar)
• Chemical of the Week – Lime
• Lime production process presentation
• Material Safety Data Sheet