Question

Why does limewater turn milky?

Answer 1

Limewater: Limewater is a clear, colourless solution of calcium hydroxide in water having molecular formula $\mathrm{Ca}(\mathrm{OH}{)}_2$.

• When carbon dioxide is passed through limewater, the solution turns milky due to the formation of Calcium carbonate.
• The balanced chemical reaction can be written as:

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

• If you keep bubbling carbon dioxide through the limewater, an acid-base reaction occurs, causing the precipitate to dissolve and give soluble calcium hydrogen carbonate:

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