Question

Give reason: When the gas formed on heating limestone is passed through freshly prepared lime water, the lime water turns milky.

Answer 1

On heating limestone(${\mathrm{CaCO}}_3$), calcium oxide and carbon dioxide are produced. The reaction is represented as:
${\text{CaCO}}_3\left(s\right)\stackrel{\Delta }{\to }\mathrm{CaO}\left(s\right)+{\mathrm{CO}}_2(\uparrow )$
When carbon dioxide is passed through lime water ($\mathrm{Ca}(\mathrm{OH}{)}_2$), it turns milky due to the formation of calcium carbonate. [1 mark]

The reaction is represented as:
$\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\left(\mathrm{aq}\right)+{\mathrm{CO}}_2(\uparrow )\to {\mathrm{CaCO}}_3\left(s\right)+H_{2}O\left(l\right)$
[1 mark]