What is the Calcium hydroxide concentration, [Ca(OH)₂], of an aqueous Ca(OH)₂ solution with a pH = 9.60?

Question

Quizplus · Accepted Answer

Calcium hydroxide, Ca(OH)2, is a strong base that dissociates completely in water according to the equation: 
Ca(OH)2(s) → Ca2+(aq) + 2 OH-(aq)

The concentration of hydroxide ions in the solution can be calculated using the pH of the solution: 
pH = -log[H+] 
9.60 = -log[H+]
[H+] = 10^-9.60 M
Since Ca(OH)2 dissociates into two hydroxide ions, the concentration of hydroxide ions is twice the concentration of Ca(OH)2: 
[OH-] = 2[H+] = 2 × 10^-9.60 M = 2 × 10^-5.40 M

The concentration of Ca(OH)2 can be calculated using the equilibrium expression: 
Ksp = [Ca2+][OH-]^2 
where Ksp is the solubility product constant for Ca(OH)2. 
The value of Ksp for Ca(OH)2 is 5.5 × 10^-6. 
Substituting the values of [OH-] and Ksp: 
5.5 × 10^-6 = [Ca2+][OH-]^2 
5.5 × 10^-6 = [Ca2+](2 × 10^-5.40)^2 
[Ca2+] = 2.0 × 10^-5 M 
Therefore, the concentration of Ca(OH)2 is 2.0 × 10^-5 M or 2.0 × 10^-5 mol/L, which corresponds to choice C.

What Is the Calcium Hydroxide Concentration, [Ca(OH)2], of an Aqueous

What Is the Calcium Hydroxide Concentration, [Ca(OH)₂], of an Aqueous