Efflorescence Definition in Chemistry

Chemistry Glossary Definition of Efflorescence

Calcium sulphate efflorescence in the rhythmites from Itu, Brazil
Calcium sulphate efflorescence in the rhythmites from Itu, Brazil. Eurico Zimbres/Wikimedia Commons/CC SA 2.5

Efflorescence is the process of losing water of hydration from a hydrate. The term means "to flower out" in French, describing the migration of a salt from a porous material to produce a coating that resembles a flower.

A good example of efflorescence may be seen in the change of appearance of copper sulfate crystals exposed to air. When freshly crystallized, copper(II) sulfate pentahydrate crystals are translucent blue. Exposure to air causes the crystals to lose water of crystallization. Efflorescence leaves a crusty white layer of anhydrous copper(II) sulfate.


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