Question

How would you distinguish between baking powder and washing soda by heating?

Answer 1

Baking powder on heating decomposes to yield sodium carbonate, water and carbon dioxide according to the following equation

NaHCO3 → Na2CO3 +H2O +CO2

Washing soda (Na2CO3.10H2O) on the other hand, on heating below 373 K loses 9 molecules of water of crystallization and forms Sodium carbonate monohydrate (Na2CO3.H2O). On heating above 373 K, this monohydrate changes to anhydrous white powder called soda ash – Na2CO3 but does not decompose further.

  Na2CO3.10H2O → Na2CO3.H2O + 9 H2O  (Below 373 K)

  Na2CO3.H2O → Na2CO3 + H2O  (above 373 K)

 Soda ash.

Thus, baking soda decomposes on heating with evolution of CO2, while washing soda loses its water of crystallization and forms soda ash but there is no evolution of CO2.

Answer 2

• THE MAIN DIFFERENCE BETWEEN BAKING SODA AND WASHING POWDER IS THAT BAKING SODA RELEASES CARBON DIOXIDE (CO2) WHILE WASHING SODA WILL NOT
• UPON HEATING BAKING POWDER (NaHCO3) , CO2 IS EVOLVED WHICH EXTINGUISHES A LIGHTED SPIRIT. OTHER TWO PRODUCTS OBTAINED ARE SODIUM CARBONATE AND WATER
• 2NaHCO3 = NaCO3+CO2 +H2O

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