Calcium oxide

Calcium oxide
	; Ionic crystal structure of calcium oxide; Ca2+ O2-
	; Powder sample of white calcium oxide
Names
	IUPAC name Calcium oxide
	Other names Lime; Quicklime; Burnt lime; Unslaked lime; Free lime (building); Caustic lime; Pebble lime; Calcia; Oxide of calcium;
Identifiers
CAS Number	1305-78-8;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:31344;
ChEMBL	ChEMBL2104397;
ChemSpider	14095;
ECHA InfoCard	100.013.763
EC Number	215-138-9;
E number	E529 (acidity regulators, ...)
Gmelin Reference	485425
KEGG	C13140;
PubChem CID	14778;
RTECS number	EW3100000;
UNII	C7X2M0VVNH;
UN number	1910
CompTox Dashboard (EPA)	DTXSID5029631 ;
	InChI InChI=1S/Ca.O Key: ODINCKMPIJJUCX-UHFFFAOYSA-N; InChI=1/Ca.O/rCaO/c1-2 Key: ODINCKMPIJJUCX-BFMVISLHAU;
	SMILES O=[Ca];
Properties
Chemical formula	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)
Solubility in water	Reacts to form calcium hydroxide
Solubility in Methanol	Insoluble (also in diethyl ether, octanol)
Acidity (pKa)	12.8
Magnetic susceptibility (χ)	−15.0×10−6 cm3/mol
Structure
Crystal structure	Cubic, cF8
Thermochemistry
Std molar; entropy (S⦵298)	40 J·mol−1·K−1
Std enthalpy of; formation (ΔfH⦵298)	−635 kJ·mol−1
Pharmacology
ATCvet code	QP53AX18 (WHO)
Hazards
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H302, H314, H315, H335
Precautionary statements	P260, P261, P264, P270, P271, P280, P301+P312, P301+P330+P331, P302+P352, P303+P361+P353, P304+P340, P305+P351+P338, P310, P312, P321, P330, P332+P313, P362, P363, P403+P233, P405, P501
NFPA 704 (fire diamond)	3 0 2 W
Flash point	Non-flammable
	NIOSH (US health exposure limits):
PEL (Permissible)	TWA 5 mg/m3
REL (Recommended)	TWA 2 mg/m3
IDLH (Immediate danger)	25 mg/m3
Safety data sheet (SDS)	ICSC 0409
Related compounds
Other anions	Calcium sulfide; Calcium hydroxide; Calcium selenide; Calcium telluride
Other cations	Beryllium oxide; Magnesium oxide; Strontium oxide; Barium oxide; Radium 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 (formula: Ca O), 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 compounds, in which carbonates, oxides, and hydroxides of calcium, silicon, magnesium, aluminium, and iron predominate. By contrast, quicklime specifically applies to the single 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 the chemical derivative calcium hydroxide (of which quicklime is the base anhydride) are important commodity chemicals.

^ ^a ^b Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). Boca Raton, FL: CRC Press. p. 4.55. ISBN 1-4398-5511-0.
^ Calciumoxid Archived 2013-12-30 at the Wayback Machine. GESTIS database
^ ^a ^b Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A21. ISBN 978-0-618-94690-7.
^ ^a ^b ^c ^d NIOSH Pocket Guide to Chemical Hazards. "#0093". National Institute for Occupational Safety and Health (NIOSH).
^ "free lime". DictionaryOfConstruction.com. Archived from the original on 2017-12-09.

[crc-1] Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). Boca Raton, FL: CRC Press. p. 4.55. ISBN 1-4398-5511-0.

[r1-2] Calciumoxid Archived 2013-12-30 at the Wayback Machine. GESTIS database

[b1-3] Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A21. ISBN 978-0-618-94690-7.

[PGCH-4] NIOSH Pocket Guide to Chemical Hazards. "#0093". National Institute for Occupational Safety and Health (NIOSH).

[5] "free lime". DictionaryOfConstruction.com. Archived from the original on 2017-12-09.

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Names
Ionic crystal structure of calcium oxide Ca²⁺ O^2-
Powder sample of white calcium oxide
IUPAC name Calcium oxide
Other names Lime Quicklime Burnt lime Unslaked lime Free lime (building) Caustic lime Pebble lime Calcia Oxide of calcium
Identifiers
CAS Number	1305-78-8
3D model (JSmol)	Interactive image
ChEBI	CHEBI:31344
ChEMBL	ChEMBL2104397
ChemSpider	14095
ECHA InfoCard	100.013.763
EC Number	215-138-9
E number	E529 (acidity regulators, ...)
Gmelin Reference	485425
KEGG	C13140
PubChem CID	14778
RTECS number	EW3100000
UNII	C7X2M0VVNH
UN number	1910
CompTox Dashboard (EPA)	DTXSID5029631
InChI InChI=1S/Ca.O Key: ODINCKMPIJJUCX-UHFFFAOYSA-N InChI=1/Ca.O/rCaO/c1-2 Key: ODINCKMPIJJUCX-BFMVISLHAU
SMILES O=[Ca]
Properties
Chemical formula	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]
Solubility in water	Reacts to form calcium hydroxide
Solubility in Methanol	Insoluble (also in diethyl ether, octanol)
Acidity (pK_a)	12.8
Magnetic susceptibility (χ)	−15.0×10⁻⁶ cm³/mol
Structure
Crystal structure	Cubic, cF8
Thermochemistry
Std molar entropy (S^⦵₂₉₈)	40 J·mol⁻¹·K⁻¹^[3]
Std enthalpy of formation (Δ_fH^⦵₂₉₈)	−635 kJ·mol⁻¹^[3]
Pharmacology
ATCvet code	QP53AX18 (WHO)
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H302, H314, H315, H335
Precautionary statements	P260, P261, P264, P270, P271, P280, P301+P312, P301+P330+P331, P302+P352, P303+P361+P353, P304+P340, P305+P351+P338, P310, P312, P321, P330, P332+P313, P362, P363, P403+P233, P405, P501
NFPA 704 (fire diamond)	3 0 2 W
Flash point	Non-flammable^[4]
NIOSH (US health exposure limits):
PEL (Permissible)	TWA 5 mg/m³^[4]
REL (Recommended)	TWA 2 mg/m³^[4]
IDLH (Immediate danger)	25 mg/m³^[4]
Safety data sheet (SDS)	ICSC 0409
Related compounds
Other anions	Calcium sulfide Calcium hydroxide Calcium selenide Calcium telluride
Other cations	Beryllium oxide Magnesium oxide Strontium oxide Barium oxide Radium oxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references