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Question:

The molar solubility of Cd(OH)₂ is 1.84 × 10⁻⁵ M in water. The expected solubility of Cd(OH)₂ in a buffer solution of pH = 12 is:

2.49 × 10⁻¹; 0M

1.84 × 10⁻⁹M

2.49 1.84 × 10⁻⁹

6.23 × 10⁻¹; 1M

Solution:

We know, Cd(OH)₂ ⇌ Cd²⁺ + 2OH⁻
Now, Ksp = 4(S)³ = 4 × (1.84 × 10⁻⁵)³
Cd(OH)₂ ⇌ Cd²⁺ + 2OH⁻
S' (10⁻² + S') ≈ 10⁻² S' × (10⁻²)² = 4 × (1.84 × 10⁻⁵)³
S' = 4 × (1.84)³ × 10⁻¹¹
S' = 2.491 × 10⁻¹⁰ M