Calcium oxide

氧化钙 (生石灰)

Calcium oxide (氧化钙 (生石灰)), formula CaO, is a oxide with a molar mass of 56.08 g/mol (CAS 1305-78-8). White solid; reacts with water rather than simply dissolving.

Key facts

Molar mass	56.08 g/mol
Category	Oxide
State at 25°C	Solid
CAS	1305-78-8

Structure

Ca²⁺ O²⁻

Ionic compound, a basic oxide

Physical properties

Appearance	White solid
Melting point	2613 °C
Boiling point	2850 °C
Density	3.34 g/cm³
Solubility	Reacts with water rather than simply dissolving

Key reactions

CaO + H₂O → Ca(OH)₂

Reacts vigorously with water, releasing heat (slaking)

CaO + CO₂ → CaCO₃

Absorbs carbon dioxide

Main uses

Slag former and flux in steelmaking
Building lime and soil conditioning
Desiccant in food packaging

Hazard

ModerateReleases heat with water and is corrosive; burns skin and eyes

Constituent elements

CaCalcium OOxygen

Data sources

CAS1305-78-8PubChem NIST WebBook CAS Common Chemistry WikipediaTextbook (general chemistry)

Molar mass is computed from IUPAC (CIAAW) standard atomic weights; formula, properties and reactions can be verified on PubChem, NIST and Wikipedia. The CAS number is the substance's unique registry identifier. Educational reference only.