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Grade 12th passPhysical Chemistry

The Ksp of Mg(OH)2 is 8.9×10-12at 25*C.If the pH of solution is adjusted to 9.0.How much Mg+2 ion will be precipitated as Mg(OH)2 from 0.1M MgCl2 solution at 25*C ? Assume that MgCl2 is completely dissociated.
​A. 0.011
​B. 0.089
​​C. 0.11
D. 0.89

Profile image of Yasir Rather
7 Years agoGrade 12th pass
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1 Answer

Profile image of Arun
6 Years ago
The products formed due to dissociation of Mg are as follows:
 
Mg⇄
 
∴  = 
 
when the formula is rearranged it yields
 
[O]= = 
 
With [O] value, pOH of the solution can be calculated as
 
pOH = -log[O]
 
pOH = -log[]
 
pOH = 5
 
As pH = 14 - pOH
 
∴ pH = 14 - 5
 
pH = 9
 
Conclusion:
 
Mg begin to precipitate from solution containing 0.1M Mg2+ ions at pH 9.