The solubility product of Mg(OH)2 is 1.2 x 10-11 . What minimum OH- concentration must be attained (for example, by adding NaOH) to decrease the Mg2+ concentration in a solution of Mg(NO3)2 to less than 1.1 x 10-10 M?
0.33
0.33-11
0
None of above
Ksp expression:
Ksp = [Mg2+] [OH]2
We set [Mg2+] = 1.1 x 10-10 and [OH] = S. Substituting into the Ksp expression:
1.2 x 10-11 = (1.1 x 10-10) (S)2
S = 0.33 M
Any sodium hydroxide solution greater than 0.33 M will reduce the [Mg2+] to less than 1.1 x 10-10 M.
Therefore, option(1) is correct.
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