To distinguish between baking powder and washing soda by heating:
- Baking powder (sodium hydrogen carbonate, NaHCO3) when heated decomposes to produce carbon dioxide (CO2) gas, water vapor, and sodium carbonate:
2NaHCO3→heatNa2CO3+CO2+H2O2\text{NaHCO}_3\xrightarrow{\text{heat}}\text{Na}_2\text{CO}_3+\text{CO}_2+\text{H}_2\text{O}2NaHCO3heatNa2CO3+CO2+H2O
The carbon dioxide gas produced can extinguish a burning matchstick and turns lime water milky.
- Washing soda (sodium carbonate decahydrate, Na2CO3- 10H2O), when heated, does not produce carbon dioxide. Instead, it loses water of crystallization:
Na2CO3⋅10H2O→heatNa2CO3+10H2O\text{Na}_2\text{CO}_3\cdot 10\text{H}_2\text{O}\xrightarrow{\text{heat}}\text{Na}_2\text{CO}_3+10\text{H}_2\text{O}Na2CO3⋅10H2OheatNa2CO3+10H2O
No gas evolution occurs, so a burning matchstick will not be extinguished, and lime water will not turn milky.
Therefore, heating baking powder results in the release of carbon dioxide gas which can be detected by its effect on a burning matchstick and lime water, while heating washing soda results only in the loss of water without gas evolution, enabling differentiation between the two substances by heating.
