Question

What will be the solubility of the $Ca(OH{)}_2$ solution when $NaOH$ is dissolved in it, compared with that in pure water?

• A. Unaffected
• B. Increased
• C. Decreased
• D. None

Answer 1

The correct option is C Decreased

The solubility of $Ca(OH{)}_2$ solution is decreased in which NaOH is dissolved, compared with that in pure water due to common ion effect. The hydroxide ion is common ion.
The dissolution of NaOH to a solution of $Ca(OH{)}_2$ will decrease the solubility of $Ca(OH{)}_2$.
$Ca(OH{)}_2$ is sparingly soluble salt.
The dissociation of $Ca(OH{)}_2$ in solution is represented by following solubility equilibrium.
$Ca\left(OH{)}_2\right(s)\to C{a}^{2+}(aq)+2O{H}^{-}(aq)$
NaOH is a strong electrolyte and completely dissociates in aqueous solution.
$NaOH\left(s\right)\to N{a}^{+}\left(aq\right)+O{H}^{-}\left(aq\right)$
The dissociation of NaOH provides hydroxide ions which are common to $Ca(OH{)}_2$. This suppresses the dissociation of $Ca(OH{)}_2$