Question

Give reason for the following:

Limewater turns milky when carbon dioxide gas is passed through it.

Answer 1

• Limewater is a calcium hydroxide solution (Ca(OH)₂).
• It is a base.
• Carbon dioxide (CO2) being a non-metallic oxide (acidic in nature), reacts with the calcium hydroxide to form calcium carbonate (CaCO3).
• The reaction involved is given below:
  $\underset{\mathrm{Calcium}\mathrm{hydroxide}}{\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\left(\mathrm{aq}\right)}+\underset{\mathrm{Carbon}\mathrm{dioxide}}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}\to \underset{\mathrm{Calcium}\mathrm{carbonate}}{{\mathrm{CaCO}}_3\left(\mathrm{s}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}$

Calcium carbonate obtained is white and insoluble in water, hence it makes limewater appear milky.