How do we find the solubility of magnesium hydroxide in water in terms of #K_(sp)#?

1 Answer
anor277
Sep 14, 2015

We write the solubility expression as before:

#Mg(OH)_2(s) rightleftharpoons Mg^(2+) + 2OH^-#

Explanation:

From the above reaction, clearly, #K_(sp) = [Mg^(2+)][OH^-]^2#. We call the solubility of the magnesium salt, #S#, and plugging this back into the equation, #K_(sp) = S xx (2S)^2 = 4S^3# (because for magnesium ion in solution there are 2 hydroxide ions!). So now you have a cubic equation and unknown #S#, which you can solve here without approximation.

#S=""^3sqrt(1/4xx1.4xx10^-4)=??*mol*L^-1#

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