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Homework Statement
If 0.12 g of magnesium hydroxide Mg(OH)2 is dissolved in sufficient water to make 500. mL of solution, what is the hydronium ion concentration in the solution? (Assume that all of the magnesium hydroxide dissolves.)
Homework Equations
pH = -log [OH-]
pOH = -log [H3O+]
The Attempt at a Solution
I got 5 * 10^-12:
Mg(OH)2 --> Mg2+ + 2OH-
[OH-] = 2.058 * 10^-3 M
pOH = 2.6852
then pH = 14 - pOH = 11.31
[H3O+] = 10^-11.30
= 5*10^-12
is this the right method, is there an easier way?