Question

Name the gas evolved when dilute hydrochloric acid reacts with sodium hydrogen carbonate. How is it recognised?

Answer 1

Reaction of dilute hydrochloric acid with sodium hydrogen carbonate will result in the evolution of ${\text{CO}}_2$ gas.
The reaction is as follow:
${\text{NaHCO}}_3\left(s\right)+\text{HCl(aq)}\to \text{NaCl}\left(aq\right)+{\text{H}}_2\text{O(l)}+{\text{CO}}_2\left(g\right)$

When the produced gas is passed through lime water, lime water turns milky which confirms that the evolved gas is carbon dixoide.
${\text{Ca(OH)}}_2\left(aq\right)+{\text{CO}}_2\left(g\right)\to {\text{CaCO}}_3\left(s\right)+{\text{H}}_2\text{O(l)}$