Question

Salt 'P', commonly used in bakery products, on heating gets converted into another salt 'Q' which itself is used for the removal of hardness of water and a gas 'R' is evolved. The gas 'R', when passed through freshly prepared lime water, turns milky. Identify 'P', 'Q' and 'R', giving a chemical equation for the justification of your answer.

Answer 1

Salt 'P', commonly used in bakery products is sodium hydrogen carbonate also known as baking soda. On heating, it gets converted into another salt 'Q' i.e. sodium carbonate which is used for the removal of hardness of water and the gas 'R' evolved is carbon dioxide.

\[\ce{\underset{\text{sodium hydrogen carbonate}}{2NaHCO3}->[heat]\underset{\text{sodium carbonate}}{Na2CO3}+\underset{\text{carbon}}{CO2}+\underset{\text{water}}{H2O}}\]

The gas 'R' i.e. CO₂ , when passed through freshly prepared lime water, turns milky due to the formation of calcium carbonate.

\[\ce{\underset{\text{calcium hydroxide}}{Ca(OH)2}+CO2-> \underset{\text{calcium carbonate}}{CaCO3}+H2O}\]