A) \[1.3\times {{10}^{-3}}M\]
B) \[2.6\times {{10}^{-2}}M\]
C) \[3.7\times {{10}^{-2}}M\]
D) \[5.8\times {{10}^{-7}}M\]
Correct Answer: C
Solution :
[c] The two \[{{K}_{sp}}\] values do not differ very much. So it is a case of simultaneous equilibria, where the concentration of any species cannot be neglected. \[\frac{\left[ S{{r}^{2+}} \right]{{\left[ {{F}^{-}} \right]}^{2}}}{\left[ S{{r}^{2+}} \right]\left[ CO_{3}^{2-} \right]}=\frac{{{K}_{s{{p}_{Sr{{F}_{2}}}}}}}{{{K}_{s{{p}_{SrC{{O}_{2}}}}}}}\] \[=\frac{7.9\times {{10}^{-10}}}{7.0\times {{10}^{-10}}}=1.128\] \[\therefore {{[{{F}^{-}}]}^{2}}=1.128\times 1.2\times {{10}^{-3}}=13.5\times {{10}^{-4}}\] \[\therefore \text{ }\left[ {{F}^{-}} \right]={{\left( 13.5\times {{10}^{-4}} \right)}^{1/2}}\] \[=3.674\times {{10}^{-2}}\approx 3.7\times {{10}^{-2}}M\]
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