Chemical And Ionic Equilibrium Result Question 31
31. The precipitate of $\mathrm{CaF}2,\left(K{\mathrm{sp}}=1.7 \times 10^{-10}\right)$ is obtained, when equal volumes of which of the following are mixed?
(1982, 1M)
(a) $10^{-4} \mathrm{M} \mathrm{Ca}^{2+}+10^{-4} \mathrm{M} \mathrm{F}^{-}$
(b) $10^{-2} \mathrm{M} \mathrm{Ca}^{2+}+10^{-3} \mathrm{M} \mathrm{F}^{-}$
(c) $10^{-5} \mathrm{M} \mathrm{Ca}^{2+}+10^{-3} \mathrm{M} \mathrm{F}^{-}$
(d) $10^{-3} \mathrm{M} \mathrm{Ca}^{2+}+10^{-5} \mathrm{M} \mathrm{F}^{-}$
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Answer:
Correct Answer: 31. ( b )
Solution:
- For precipitation reaction,,$\quad Q_{\mathrm{IP}} > K_{\text {sp }}$.
$\begin{aligned} Q_{\mathrm{IP}} & =\left[\mathrm{Ca}^{2+}\right]\left[\mathrm{F}^{-}\right]^2=\left(\frac{10^{-2}}{2}\right) \times\left(\frac{10^{-3}}{2}\right)^2 \\ & =1.25 \times 10^{-9} > K_{\text {sp }}, \text { precipitate will be formed. } \end{aligned}$
BETA
