What concentration of hydroxide ions (OH-) is needed to begin the formation of Pb(OH)2 in a solution with a [Pb2+] of 4.5 x 10^-5 M, given that the solubility product constant (Ksp) of Pb(OH)2 is 8.0 x 10^-15?

• A. 1.3 x 10^-5 M
• B. 4.2 x 10^-5 M
• C. 1.3 x 10^-4 M
• D. 2.7 x 10^-5 M

Answer: (C)

Verified step by step guidance

1. Understand the problem: We need to find the concentration of hydroxide ions (OH-) required to start forming Pb(OH)2 in a solution with a given concentration of Pb2+ ions. The solubility product constant (Ksp) for Pb(OH)2 is provided.
2. Write the balanced chemical equation for the dissolution of Pb(OH)2: Pb(OH)2 (s) ⇌ Pb2+ (aq) + 2OH- (aq).
3. Express the solubility product constant (Ksp) in terms of the concentrations of the ions: Ksp = [Pb2+][OH-]^2.
4. Substitute the given values into the Ksp expression: 8.0 x 10^-15 = (4.5 x 10^-5)[OH-]^2.
5. Solve for [OH-]: Rearrange the equation to isolate [OH-]^2 and then take the square root to find the concentration of OH- needed to begin the formation of Pb(OH)2.