Question

Washing soda, Na₂CO₃ • 10H₂O, loses water when exposed to atmosphere. What is the name given to this phenomenon?

Answer 1

this prodded is called dehydration

Answer 2

Efflorescence is a phenomenon where certain crystalline salts lose part or all of their water of crystallization when exposed to the atmosphere to form the anhydrous salts or what is called lower dehydrate. An example of efflorescent salt is is washing soda (sodium carbonate decahydrate) that loses nine out of its ten molecules of water of crystallization when exposed to the atmosphere.

Na2CO3.10H2O(s) → Na2CO3.H2O(s) + 9H2O(g)