Equilibrium Question 842
Question: A solution of $ NH_4Cl $ and $ NH_3 $ has pH = 8.0. Which of the following hydroxides may be precipitated when this solution is mixed with equal volume of 0.2 M of metal ion.
Options:
A) $ Ba{{( OH )}_2}( K _{sp}=1.1\times {10^{-4}} ) $
B) $ Mg{{( OH )}_2}( K _{sp}=3.5\times {10^{-4}} ) $
C) $ Fe{{(OH)}_2}( K _{sp}=8.1\times {10^{-16}} ) $
D) $ Ca{{( OH )}_2}( K _{sp}=2.1\times {10^{-5}} ). $
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Answer:
Correct Answer: C
Solution:
$ pH=8,pOH=6;[O{H^{-}}]={10^{-6}}M $ Ionic product of $ Fe{{(OH)}_2}=0.2\times {{(1\times {10^{-6}})}^{2}} $
$ =2\times {10^{-13}}>K _{sp}( =8.1\times {10^{-16}} ) $
