An aryl carboxylic acid on treatment with sodium hydrogen carbonate liberates a gaseous molecule. Identify the gas molecule liberated.

The carboxylic acids like alcohols evolve hydrogen with electropositive metals and form salts with alkalies similar to phenols. However, unlike phenols they react with weaker bases such as carbonates and hydrogencarbonates to evolve carbon dioxide. This reaction is used to detect the presence of carboxyl group in an organic compound.

$\mathrm{RCOOH} + {\mathrm{NaHCO}}_3\stackrel{}{\to }\mathrm{RCOONa} + {\mathrm{CO}}_2 + {\mathrm{H}}_2\mathrm{O}$