Question

Among the following hydroxides, the one which has the lowest value of $K_{sp}$ at ordinary temperature is :

• A. $Mg(OH{)}_2$
• B. $Ca(OH{)}_2$
• C. $Ba(OH{)}_2$
• D. $Be(OH{)}_2$

Answer 1

The correct option is D $Be(OH{)}_2$

It is $Be(OH{)}_2$ with a $K_{sp}$ in the ${10}^{-22}$ range.

This is due to the fact that the $B{e}^{2+}$ ion is smaller than the other metal ions among the choices, which results in a tighter bond with the $O{H}^{-}$ ions, thus much lower solubility.

Moving downward in group 2A, the $K_{sp}$'s increase due to increasing side of the metal ions and the weakening of the bond between the metal and $O{H}^{-}$ ions.