The molar solubility of Ca(OH)₂ was experimentally determined to be 0.020 M. Based on this value, what is the Ksp of Ca(OH)₂?

• A. 4.0 x 10⁻⁴
• B. 1.6 x 10⁻⁵
• C. 8.0 x 10⁻⁶
• D. 2.0 x 10⁻³

Answer: (B)

Verified step by step guidance

1. Start by writing the balanced chemical equation for the dissolution of calcium hydroxide in water: Ca(OH)₂(s) ⇌ Ca²⁺(aq) + 2OH⁻(aq).
2. Identify the stoichiometry of the dissolution process. For every mole of Ca(OH)₂ that dissolves, 1 mole of Ca²⁺ and 2 moles of OH⁻ are produced.
3. Express the molar solubility of Ca(OH)₂ in terms of the concentrations of the ions. If the molar solubility is 0.020 M, then [Ca²⁺] = 0.020 M and [OH⁻] = 2 × 0.020 M = 0.040 M.
4. Write the expression for the solubility product constant (Ksp) for Ca(OH)₂: Ksp = [Ca²⁺][OH⁻]².
5. Substitute the concentrations of the ions into the Ksp expression: Ksp = (0.020 M) × (0.040 M)². Calculate this expression to find the Ksp value.