Question

In the system, $Ca{F}_2\left(s\right)\rightleftharpoons {Ca}^{+2}\left(aq\right)+2F^{-}$ increasing the concentration of ${Ca}^{2+}$ ions four times will cause the equilibrium concentration of $F^{-}$ ions to change to .......... times the initial value.

• A. $4$
• B. $\frac{1}{2}$
• C. $2$
• D. $\frac{1}{4}$

Answer 1

The correct option is B $\frac{1}{2}$

$Ca{F}_2\left(s\right)\rightleftharpoons {Ca}^{+2}\left(aq\right)+2F^{-}$

$S$ $2S$

As we change concentration of $C{a}^{+2}$ ion, $K_{sp}$ will remain same. Therefore,

$K_{sp}=4S^3=4S\times (2S^{\prime }{)}^2$

$S^{\prime }=\frac{S}{2}$

So, the equilibrium concentration of $F^{-}$ will decrease to $\frac{1}{2}$ times the initial value.