Explain with the help of a chemical equation why lime water turns milky on passing carbon dioxide gas through it.

• Lime water turns milky on passing carbon dioxide gas through it, due to the formation of calcium carbonate.
• This calcium carbonate is a milky white precipitate.
• This is a type of precipitation reaction.

The reaction can be represented as the following chemical equation:

$\underset{\mathrm{Calcium}\mathrm{hydroxide}(\mathrm{lime}\mathrm{water})}{\mathrm{Ca}{\left(\mathrm{OH}\right)}_2}+\underset{\mathrm{Carbon}\mathrm{dioxide}}{{\mathrm{CO}}_2}\to \underset{\mathrm{Calcium}\mathrm{carbonate}}{{\mathrm{CaCO}}_3\downarrow }+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}}$