Overview

Calcium oxide (KAL-see-um OK-side) is an odorless crystalline or powdery solid that, in a pure form, is white to off-gray. It often appears with a yellowish or brownish tint to the presence of impurities, especially iron. Calcium oxide reacts with water to form calcium hydroxide (Ca(OH)₂) with the evolution of significant amounts of heat. The compound is strongly caustic.

Key Facts

Other Names:

Lime; quicklime; burnt lime; calx; unslaked lime; fluxing lime

Formula:

CaO

Elements:

Calcium, oxygen

Compound Type:

Metallic oxide

State:

Solid

Molecular Weight:

56.08 g/mol

Melting Point:

2,898°C (5,248°F)

Boiling Point:

Not available

Solubility:

Reacts with water to form calcium hydroxide; soluble in acids; insoluble in alcohol and most organic solvents

Calcium oxide has been known since ancient times. The Roman writer Cato the Elder (234–149 BCE) described one method of producing the compound in 184 BCE. Another early Roman scholar, Pliny the Elder...