Question

The precipitate of $Ca{F}_2(K_{sp}=1.7\times {10}^{-10})$ is obtained when equal volumes of the following are mixed :

• A. ${10}^{-4}MC{a}^{2+}+{10}^{-4}M{F}^{-}$
• B. ${10}^{-2}MC{a}^2+{10}^{-3}M{F}^{-}$
• C. ${10}^{-5}MC{a}^2+{10}^{-3}M{F}^{-}$
• D. ${10}^{-3}MC{a}^2+{10}^{-5}M{F}^{-}$

Answer 1

Answer: (B)

${10}^{-2}MC{a}^2+{10}^{-3}M{F}^{-}$

$I_p=\left[C{a}^{2+}\right][F^{-}{]}^2>K_{sp}$ for precipitate formation.

Now,

$I_p=\left[C{a}^{2+}\right][F^{-}{]}^2={10}^{-2}\times ({10}^{-3}{)}^2={10}^{-8}>K_{sp}$

Precipitation happens in B option.