A saturated solution of magnesium hydroxide is kept at a pH 9.50. Calculate the concentration of of Mn2 . (4 pts)

The concentration of Mg²⁺ is 1.58x10⁻⁵ mol.l⁻¹

Explanation:

Mg(OH)₂ ⇔ Mg²⁺ + 2OH⁻

The solution is said to be kept at pH 9.50

Since; pH + pOH = 14

Making pOH the subject,

∴ pOH = 14 - pH

           = 14 - 9.50

           = 4.50

since; pOH = -log[OH⁻]

∴ -log[OH⁻] = 4.50

[OH⁻] = Antilog (-4.5)

         = Antilog (-4.5+5.5)

         = 3.16 x 10⁻⁵ mol.l⁻¹

The chemical equation shows that [Mg²⁺] is half of OH ion concentration.

Therefore,

[Mg²⁺] =

[Mg²⁺] = 1.58x10⁻⁵ mol.l⁻¹