Equilibrium Question 230

Question: What is the solubility of calcium fluoride in a saturated solution, if its solubility product is $ 3.2\times {10^{-11}} $ [CPMT 1997]

Options:

A) $ 2.0\times {10^{-4}},mole/litre $

B) $ 12.0\times {10^{-3}},mole/litre $

C) $ 0.2\times {10^{-4}},mole/litre $

D) $ 2\times {10^{-3}},mole/litre $

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Answer:

Correct Answer: A

Solution:

$ \underset{S}{\mathop{CaF_2}}, $ ⇌ $ \underset{S,}{\mathop{C{a^{++}}}},+\underset{{{(2S)}^{2,}}}{\mathop{2{F^{-}}}}, $

$ K _{sp}=4S^{3} $

$ S=\sqrt[3]{\frac{K _{sp}}{4}} $

$ =\sqrt[3]{\frac{3.2\times {10^{-11}}}{4}} $

$ =2\times {10^{-4}} $ m/l.



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