Question

Which gas is given off when dilute hydrochloric acid is added to calcium carbonate?

Answer 1

When calcium carbonate(${\mathrm{CaCO}}_3$) reacts with dil hydrochloric acid ($\mathrm{HCl}$), calcium chloride (${\mathrm{CaCl}}_2$) is formed along with water (${\mathrm{H}}_2\mathrm{O}$) and carbon dioxide (${\mathrm{CO}}_2$)gas.

The following reaction takes place:

$\underset{\mathrm{calcium}\mathrm{carbonate}}{{\mathrm{CaCO}}_3\left(\mathrm{s}\right)}+\underset{\mathrm{hydrochloric}\mathrm{acid}}{\mathrm{HCl}\left(\mathrm{aq}\right)}\to \underset{\mathrm{calcium}\mathrm{chloride}}{{\mathrm{CaCl}}_2\left(\mathrm{s}\right)}+\underset{\mathrm{carbon}\mathrm{dioxide}}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}$

So carbon dioxide gas is released during this reaction.

Test to detect the presence of carbon dioxide gas.

The gas produced when passed through lime water turns milky due to the formation of a white precipitate of calcium carbonate. The following reaction takes place:

$\underset{\mathrm{calcium}\mathrm{hydroxide}}{\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\left(\mathrm{aq}\right)}+\underset{\mathrm{carbon}\mathrm{dioxide}}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}\to \underset{\mathrm{calcium}\mathrm{carbonate}}{{\mathrm{CaCO}}_3}\downarrow +\underset{\mathrm{water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}$