Give the characteristic test for ${\mathrm{CO}}_2$ gas.

Carbon dioxide:

1. One carbon and two oxygen atoms are linked together to form carbon dioxide. It is a colorless and odorless gas that dissolves in water, ethanol, and acetone.
2. It can be identified by a lime water test. Lime water is generally a solution of calcium hydroxide.
3. When we bubble carbon dioxide into the solution, it combines with the calcium hydroxide to form a white calcium carbonate precipitate.
4. The limewater turns milky.

$\underset{\mathrm{Calcium}\mathrm{hydroxide}}{\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\left(\mathrm{aq}\right)}+\underset{\mathrm{Carbon}\mathrm{dioxide}}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}\to \underset{\mathrm{Calcium}\mathrm{carbonate}(\mathrm{PPt}.)}{{\mathrm{CaCO}}_3}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}$

5. If more ${\mathrm{CO}}_2$ is released, more carbonic acid is produced, which reacts with the calcium carbonate to generate calcium hydrogen carbonate, which is soluble, causing the precipitate to dissolve.

$\underset{\mathrm{Calcium}\mathrm{carbonate}}{{\mathrm{CaCO}}_3\left(\mathrm{s}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}+\underset{\mathrm{Carbon}\mathrm{dioxide}}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}\to \underset{\mathrm{Cacium}\mathrm{hydrogencarbonate}}{\mathrm{CaH}{\left({\mathrm{CO}}_3\right)}_2\left(\mathrm{aq}\right)}$

Therefore, ${\mathrm{CO}}_2$ can be characterized by the lime water test.