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Solubility with Common Ion

  • #1
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Homework Statement


What is the solubility of Mg(OH)2 in a solution buffered at pH 8.80.


Homework Equations





The Attempt at a Solution


The answer is .45 M or 26 g/L but I can't get that for some reason.

I can find the concentration of hydroxide [OH-] = 6.3 x 10-6
Mg(OH)2 -> Mg+2 + 2OH-
................0+x,....6.3x10-6 + 2x

1.8x10-11 = x(6.3x10-6 + 2x)^2

x = 1.65 x 10-4 M (neglecting the 6.3 x10-6)
I've also tried solving the cubic with similar results.
Does anyone where I went wrong?
 

Answers and Replies

  • #2
Borek
Mentor
28,353
2,742
Solution is buffered. [OH-] is not 6.3x10-6 + 2x but JUST 6.3x10-6.
 

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