Question

A saturated solution of $Ca{F}_2$ is $2\times {10}^{-4}mol/L$ Its solubility product constant is:

• A. $2.6\times {10}^{-9}$
• B. $4\times {10}^{-8}$
• C. $8\times {10}^{-12}$
• D. $3.2\times {10}^{-11}$
• E. $8\times {10}^{-10}$

Answer 1

Answer: (D)

Solubility of $Ca{F}_2=2\times {10}^{-4}mol{L}^{-1}$ Each mole of $Ca{F}_2$ dissolving in $H_{2}O$ gives one mole of $C{a}^{2+}$ and two moles of $F^{-}$ ions. $Ca{F}_{2}C{a}^{2+}+2F^{-}$ $2\times {10}^{-4}M.2\times 2\times {10}^{-4}M$ $K_{sp}=[C{a}^{2+}]{[F^{-}]}^2$ $=[2\times {10}^{-4}]{[2\times 2\times {10}^{-4}]}^2$ $K_{sp}=3.2\times {10}^{-11}$