Bleaching powder is prepared by passing chlorine gas $\left({\mathrm{Cl}}_2\right)$through a solution of calcium hydroxide $\mathrm{Ca}(\mathrm{OH}{)}_2$.

The reaction that occurs is, ${\text{Ca(OH)}}_{\text{2}}{\text{+Cl}}_{\text{2}}{\text{ (g)→CaOCl}}_{\text{2}}{\text{+H}}_{\text{2}}\text{O.}$

When an excess of calcium oxide is added to water, ${\text{Ca(OH)}}_{\text{2}}$ forms,

${\text{CaO+H}}_{\text{2}}{\text{O→Ca(OH)}}_{\text{2}}$

It partially dissolves in water to produce a solution called lime water, which is a moderate base.

${\text{Ca(OH)}}_2$ is highly basic and antibacterial due to which it is used as a disinfectant.