Calcium oxide
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| Names | |
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IUPAC name
Calcium oxide
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| Other names
Quicklime, burnt lime, unslaked lime, pebble lime
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| Identifiers | |
| 1305-78-8 | |
| 3D model (Jmol) | Interactive image |
| ChEBI | CHEBI:31344 |
| ChEMBL | ChEMBL2104397 |
| ChemSpider | 14095 |
| ECHA InfoCard | 100.013.763 |
| E number | E529 (acidity regulators, ...) |
| 485425 | |
| PubChem | 14778 |
| RTECS number | EW3100000 |
| UNII | C7X2M0VVNH |
| UN number | 1910 |
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| 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 | 3,850 °C (6,960 °F; 4,120 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 | |
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Std molar
entropy (S |
40 J·mol−1·K−1 |
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Std enthalpy of
formation (ΔfH |
−635 kJ·mol−1 |
| Pharmacology | |
| QP53AX18 (WHO) | |
| Hazards | |
| Safety data sheet | Hazard.com |
| NFPA 704 | |
| Flash point | Non-flammable |
| US health exposure limits (NIOSH): | |
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PEL (Permissible)
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TWA 5 mg/m3 |
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REL (Recommended)
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TWA 2 mg/m3 |
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IDLH (Immediate danger)
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25 mg/m3 |
| Related compounds | |
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Other anions
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Calcium sulfide Calcium hydroxide |
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Other cations
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Beryllium oxide Magnesium oxide Strontium oxide Barium oxide |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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| 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 which 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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Wikipedia