Baking soda (NaHCO3) on heating produces carbon dioxide (CO2). Carbon dioxide turns lime water milky. It can also extinguish a burning matchstick.
Whereas heating washing soda (Na2CO3.10H2O) does not produce any such gas and hence there is no effect on lime water or a burning matchstick. The water of crystallisation in washing soda is released due to heating and the salt becomes anhydrous white powder called soda ash.
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