E

Efflorescence

Hydrated salt losing water in air: M·nH₂O(s) → M·(n-x)H₂O(s) + xH₂O(g)
Quick Reference
Formula / NotationHydrated salt losing water in air: M·nH₂O(s) → M·(n-x)H₂O(s) + xH₂O(g)
Also Known AsWater loss from hydrate, efflorescing salt, dehydration of hydrate

What is Efflorescence?

The process by which a hydrated salt loses its water of crystallization to the atmosphere, resulting in a powdery surface coating. Washing soda (Na₂CO₃·10H₂O) effloresces in dry air to form anhydrous sodium carbonate. Opposite of deliquescence.

Formula & Notation

Hydrated salt losing water in air: M·nH₂O(s) → M·(n-x)H₂O(s) + xH₂O(g)

Other Names / Synonyms: Water loss from hydrate, efflorescing salt, dehydration of hydrate

Properties & Characteristics

Efflorescence is the spontaneous loss of water of crystallisation from a hydrated salt when exposed to air, resulting in a powdery, white surface coating. It occurs when the vapour pressure of water over the hydrate exceeds the partial pressure of water vapour in the surrounding air. Classic examples: washing soda (Na₂CO₃·10H₂O) effloresces in dry air, CuSO₄·5H₂O loses water slowly at low humidity.

Uses & Applications

Efflorescence is relevant in preserving hydrated chemicals (store in sealed containers or at appropriate humidity), in understanding cement and concrete weathering (calcium silicate hydrates), in art conservation (salt damage in ancient buildings and frescoes), and in pharmaceutical tablet stability (hydrate polymorphs).

Safety Information

Effloresced powders may be more reactive or have different handling properties than the original hydrate. Sudden loss of water of crystallisation can change the mass of a weighed sample, leading to errors in quantitative analysis. Store hygroscopic and efflorescent materials appropriately sealed.

Always consult the SDS/MSDS before handling any chemical. This information is for educational purposes only.

Key Facts

Term Efflorescence
Formula Hydrated salt losing water in air: M·nH₂O(s) → M·(n-x)H₂O(s) + xH₂O(g)
Synonyms Water loss from hydrate, efflorescing salt, dehydration of hydrate

Frequently Asked Questions

The process by which a hydrated salt loses its water of crystallization to the atmosphere, resulting in a powdery surface coating. Washing soda (Na₂CO₃·10H₂O) effloresces in dry air to form anhydrous sodium carbonate. Opposite of deliquescence.

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