Q1 / 170 · Manipal (MET) 2019 · Chemistry

The solubility $\mathrm{CaF}_2$ is $s$ moles/litre. Then solubility product is

  • A
    $s^2$
  • Correct answer
    B
    $4 s^3$
  • C
    $3 s^2$
  • D
    $s^3$

Solution

$\begin{gathered}\mathrm{CaF}_{\mathrm{s}} \rightleftharpoons \mathrm{Ca}^{2+}+2 \mathrm{~F}^{-} \\ {\left[\mathrm{Ca}^{2+}\right]=s} \\ {\left[\mathrm{~F}^{-}\right]=2 s} \\ K_{\text {sp }}=\left[\mathrm{Ca}^{2+}\right] \cdot\left[\mathrm{F}^{-}\right]^2=s \cdot(2 s)^2 \\ K_{\text {sp }}=4 s^3\end{gathered}$

Hence, the correct answer is option: 'B'.

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