Magnesium hydroxide and sodium hydroxide are both strong bases. The pH of a saturated solution of sodium hydroxide is greater than 14. The pH of a saturated solution of magnesium hydroxide is about 10.2. Why do the solutions have different pH values?

Solubility of NaOH is greater and there are more OH- ions in solution.

Explanation: Reactions : NaOH (s) ⇒ Na+ (aq) + OH- (aq)

Mg(OH)2 (s) ⇒ Mg2+ (aq) + 2 OH-(aq)

Although in same amount of moles, Mg(OH)2 produces

two (OH-)-ions in water solution, solubility of Mq(OH)2 is smaller.

Concentration [OH-]ions is smaller in saturated  water solution

of Mg(OH)2

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