Ksp AAMC#8

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A sparingly soluable metal hydroxide, M(OH)2 has a molar solubility of s mol/L at 25 C. Its Ksp value is?


The answer is 4s^3.

Why? I dont understand this at all, even with the AAMC answer given.
So one of you experts please help me out...

 

[N1st]

A sparingly soluable metal hydroxide, M(OH)2 has a molar solubility of s mol/L at 25 C. Its Ksp value is?


The answer is 4s^3.

Why? I dont understand this at all, even with the AAMC answer given.
So one of you experts please help me out...

When M(OH)2 dissociates it does so into one part M and 2 parts OH. Ksp is the product of the concentrations of the dissociated ions to the powers of their stoichiometric coefficients.

Ksp = [M] * [OH]^2 = s * (2s)^2 = 4s^3.