Question

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

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

Answer 1

Answer: (B)

${10}^{-2}M{Ca}^{2+}+{10}^{-3}M{F}^{-}$

The ionic product $IP=\left[C{a}^{2+}\right][F^{-}{]}^2$

$IP={10}^{-2}\times ({10}^{-3}{)}^2$

$IP={10}^{-8}$

The ionic product exceeds solubility product.
$K_{sp}=(1.7\times {10}^{-10})$

A precipitate will be formed when $IP>SP$