Question

Washing soda loses its water of crystallization when exposed to air due to the phenomenon called _________.

Answer 1

Efflorescence:

• Efflorescence is the property of some salts to lose their water of crystallization when their crystals are exposed to dry air.
• In such cases crystals become powdery, and such substances are called efflorescent substances.
• When washing soda (Sodium carbonate decahydrate) is exposed to dry air for a short duration of time its water of crystallization goes away to give monohydrate.

$\underset{(\mathrm{Washing}\mathrm{soda})}{{\mathrm{Na}}_2{\mathrm{CO}}_3.10{\mathrm{H}}_2\mathrm{O}\left(\mathrm{s}\right)}\stackrel{\mathrm{dry}\mathrm{air}}{\to }\underset{(\mathrm{Sodium}\mathrm{carbonate}\mathrm{monohydrate})}{{\mathrm{Na}}_2{\mathrm{CO}}_3.{\mathrm{H}}_2\mathrm{O}\left(\mathrm{s}\right)}+\underset{\left(\mathrm{Water}\right)}{9{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}$.

Therefore, Washing soda loses its water of crystallization when exposed to air due to the phenomenon called efflorescence.