Calcium hydroxide is partially soluble as shown by the

following reaction:

Ca (OH) 2 (s) → Ca2 + (aq) + 20H (aq)

What is the pOH of a 5 x 10-5 M Ca (OH) 2 solution?

pH = __

Enter the answer

4

10

Explanation:

The reaction equation is given as;

Ca (OH) ₂ → Ca²⁺ + 2OH⁻

Concentration of Ca (OH) ₂ = 5 x 10⁻⁵M

Unknown:

pOH of the solution = ?

pH of the solution = ?

Solution:

Solve for the pOH of this solution using the expression below obtained from the ionic product of water;

pOH = ⁻log₁₀[OH⁻]

Ca (OH) ₂ → Ca²⁺ + 2OH⁻

1moldm⁻³ 1moldm⁻³ 2 x 1moldm⁻³

5 x 10⁻⁵moldm⁻³ 5 x 10⁻⁵moldm⁻³ 2 (5 x 10⁻⁵moldm⁻³)

1 x 10⁻⁴moldm⁻³

Therefore;

pOH = - log₁₀ 1 x 10⁻⁴ = 4

Since

pOH + pH = 14

pH = 14 - 4 = 10