Question

Name the gas evolved when dilute HCl reacts with sodium hydrogencarbonate. How is it recognised?

Answer 1

Carbon dioxide gas is liberated when dilute hydrochloric acid reacts with sodium hydrogen carbonate.

\[\ce{\underset{hydrogen carbonate}{\underset{Sodium}{NaHCO3_{(s)}}} + \underset{chloride}{\underset{Hydrogen}{HCl_{(aq)}}} -> \underset{chloride}{\underset{Sodium}{NaCl_{(aq)}}} + \underset{Water}{H2O_{(l)}} + \underset{dioxide}{\underset{Carbon}{CO2}}\uparrow}\]

When the gas liberated in the reaction is passed through lime water, lime water turns milky or a white precipitate of calcium carbonate is formed. This confirms that the gas is carbon dioxide.

\[\ce{\underset{(Lime water)}{\underset{Calcium hydroxide}{Ca(OH)2_{(aq)}}} + CO2_{(g)} -> \underset{precipitate}{\underset{White}{CaCO3_{(s)}}} + H2O_{(l)}}\]