Question

Hydrochloric acid reacts with crushed egg shells to give a gas that turns limewater milky. Identify the gas evolved.

• A. Carbon monoxide
• B. Oxygen
• C. Carbon dioxide
• D. Hydrogen

Answer 1

The correct option is C Carbon dioxide

Egg shell contains calcium carbonate (${\text{CaCO}}_3$). It reacts with hydrochloric acid ($\text{HCl}$ ) to give calcium chloride (${\text{CaCl}}_2$), carbon dioxide gas (${\text{CO}}_2$) along with water (${\text{H}}_2\text{O}$). The reaction involved is given below:

${\text{CaCO}}_3\text{(s)}+2\text{HCl(aq)}\to {\text{CaCl}}_2\text{(aq)}+{\text{H}}_2\text{O(l)}+{\text{CO}}_2\text{(g)}$

The evolved carbon dioxide gas turns limewater ${\text{(Ca(OH)}}_2)$ milky. The milkiness is due to the formation of insoluble calcium carbonate. The reaction of limewater with carbon dioxide is given below:

${\text{CO}}_2\text{(g)}+{\text{Ca(OH)}}_2\text{(aq)}\to {\text{CaCO}}_3\text{(s)}+{\text{H}}_2\text{O(l)}$