- **Problem** At $25^{\circ} {C}$, the solubility product of $Mg(OH)_2$ is $1.1\times 10^{-11}$. At which pH, will
- $Mg^{2+}$ ions start precipitating in the form of $Mg(OH)_2$ from a solution of $0.001 M Mg^{2+}$
- ions ?
- **Solution**
- $ K_{s p}=K_w$
- $ K_{SP}=[Mg^{2+}][OH^{-}]^2$
- $1.1 \times 10^{-11}=[Mg^{2+}][OH^{-}]^2$
- $[OH^-]^2=\frac{1.1 \times 10^{-11}}{.001}$
- $[OH^-]^2 = 1.1 \times 10^{-8}$
- $[OH^-] \approx 1 \times 10^{-4}$
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