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Q.
When washing soda is heated:
AFMCAFMC 2005
Solution:
Washing soda is sodium carbonate decahydrate $\left( Na _{2} CO _{3} \cdot 10 H _{2} O \right)$. It is an efflorescent substance i.e., give out nine water molecules of crystallization on keeping in air
$Na _{2} CO _{3} \cdot 10 H _{2} O \xrightarrow{\text { air }} \underset{\text{Sodium carbonate monohydrate}}{Na _{2} CO _{3} \cdot H _{2} O +9 H _{2} O}$
But on heating it losses all water molecules to form anhydrous sodium carbonate or soda ash
$Na_2CO_3 \cdot 10H_2O \xrightarrow{\Delta} \underset{\text{(Soda ash)}}{Na_2CO_3} + 10H_2O$