Question

What happens when ${\mathrm{CO}}_2$ gas is passed through lime water for a long time?

Answer 1

When carbon dioxide combines with limewater, a colorless solution of calcium hydrogen carbonate$\left[\mathrm{Ca}{\left({\mathrm{HCO}}_3\right)}_2\right]$ is formed.

Lime water - A saturated aqueous solution of calcium hydroxide$\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$ is known as limewater.

The steps in the reaction of lime water and ${\mathrm{CO}}_2$ gas

$$\begin{gathered} \mathrm{Ca}{\left(\mathrm{OH}\right)}_2\left(\mathrm{aq}\right)+{\mathrm{CO}}_2\left(\mathrm{g}\right)\to {\mathrm{CaCO}}_3\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \\ {\mathrm{CaCO}}_3\left(\mathrm{s}\right)+{\mathrm{CO}}_2\left(\mathrm{g}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to \mathrm{Ca}{\left({\mathrm{HCO}}_3\right)}_2\left(\mathrm{aq}\right) \end{gathered}$$

This reaction can be used as a test to detect the production of ${\mathrm{CO}}_2$ gas in a reaction. At first, calcium carbonate$\left({\mathrm{CaCO}}_3\right)$ precipitates as a white solid giving the mixture a milky appearance. Then on adding more ${\mathrm{CO}}_2$ gas the solution becomes colorless due to the formation of calcium hydrogen carbonate $\left[\mathrm{Ca}{\left({\mathrm{HCO}}_3\right)}_2\right]$

Therefore, when ${\mathrm{CO}}_2$ gas is passed through lime water for a long time a colorless solution of calcium hydrogen carbonate$\left[\mathrm{Ca}{\left({\mathrm{HCO}}_3\right)}_2\right]$ is formed.