1. Write the balanced dissolution equation:
Mg(OH)₂(s) ⇌ Mg²⁺(aq) + 2OH⁻(aq)
2. Define the molar solubility:
The molar solubility (s) is the concentration of the dissolved metal cation in a saturated solution. In this case, s = 1.4 x 10⁻⁴ M.
3. Express the ion concentrations in terms of 's':
* [Mg²⁺] = s = 1.4 x 10⁻⁴ M
* [OH⁻] = 2s = 2 * (1.4 x 10⁻⁴ M) = 2.8 x 10⁻⁴ M
4. Write the Ksp expression:
Ksp = [Mg²⁺][OH⁻]²
5. Substitute the ion concentrations and calculate Ksp:
Ksp = (1.4 x 10⁻⁴ M)(2.8 x 10⁻⁴ M)²
Ksp = 1.09 x 10⁻¹¹
Therefore, the Ksp of magnesium hydroxide is 1.09 x 10⁻¹¹.
