Question

If you have saturated solution of $Ca{F}_2$, then:

• A. $\left[{Ca}^{2+}\right]=\sqrt{K_{sp}}$
• B. $\left[{Ca}^{2+}\right]=2\left[F^{-}\right]$
• C. $2\left[{Ca}^{2+}\right]=\left[F^{-}\right]$
• D. $\left[{Ca}^{2+}\right]={\left[K_{sp/4}\right]}^{1/3}$

Answer 1

Answer: (C), (D)

The correct options are
C $2\left[{Ca}^{2+}\right]=\left[F^{-}\right]$
D $\left[{Ca}^{2+}\right]={\left[K_{sp/4}\right]}^{1/3}$

$Ca{F}_2\rightleftharpoons C{a}^{2+}+2F^{-}$

$S$ $2S$

So $\left[C{a}^{2+}\right]=S$ and $\left[F^{-}\right]=2S=2\left[C{a}^{2+}\right]$

$K_{sp}=\left[C{a}^{2+}\right][F^{-}{]}^2=S(2S{)}^2=4S^3$

$S=[K_{sp}/4{]}^{1/3}=[C{a}^{2+}]$