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Chemistry Equilibrium of a Sparingly Soluble Ionic Compound

Homework Statement
I can't get the correct answer, isn't it if Ksp>[Mn2+][OH-]^2, there is no precipitation. How to get the specific concentration of [OH-]?
Homework Equations
Kb = [NH4+][OH-]/[NH3]
Ksp=[Mn2+][OH-]^2
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Answer given is 6.61g.
 

Borek

Mentor
28,094
2,614
You are looking for the highest concentration of OH- that doesn't produce precipitation, don't you?
 
chemistry.jpeg


May I know which step is wrong? thanks
 

mjc123

Science Advisor
842
389
You have worked out the concentration in g/L. What is the mass in the actual solution?
 
chemistry.jpeg


Is this correct ? thanks.
 

mjc123

Science Advisor
842
389
It is not quite equal to the given answer; I think that's because you rounded off [OH-] to 1.4e-6 M instead of 1.435e-6 M. Keep the extra digits through the calculation, and round off to the appropriate sig figs at the end.
 

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