Multiple Choice
Calculate the molar solubility of magnesium fluoride (MgF2) in a solution that is 0.350 M in NaF. For magnesium fluoride, Ksp = 5.16 x 10^-11.
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18. Aqueous Equilibrium
Solubility Product Constant: Ksp
Multiple Choice
Calculate the solubility (in grams per 1.00×10² mL of solution) of magnesium hydroxide (Mg(OH)₂) in a solution buffered at pH = 10, given that the Ksp of Mg(OH)₂ is 1.8 × 10⁻¹¹.
A
0.15 g
B
0.0015 g
C
0.015 g
D
0.00015 g
Verified step by step guidance1
First, write the dissolution equation for magnesium hydroxide: \( \text{Mg(OH)}_2 (s) \rightleftharpoons \text{Mg}^{2+} (aq) + 2\text{OH}^- (aq) \).
Next, express the solubility product constant (Ksp) for this equilibrium: \( K_{sp} = [\text{Mg}^{2+}][\text{OH}^-]^2 \). Given \( K_{sp} = 1.8 \times 10^{-11} \).
Since the solution is buffered at pH = 10, calculate the concentration of \( \text{OH}^- \) ions using the relation \( pH + pOH = 14 \). Thus, \( pOH = 4 \) and \( [\text{OH}^-] = 10^{-4} \text{M} \).
Substitute \( [\text{OH}^-] = 10^{-4} \text{M} \) into the Ksp expression: \( 1.8 \times 10^{-11} = [\text{Mg}^{2+}](10^{-4})^2 \). Solve for \( [\text{Mg}^{2+}] \).
Convert the molar solubility of \( \text{Mg}^{2+} \) to grams per 100 mL of solution. Use the molar mass of \( \text{Mg(OH)}_2 \) to find the solubility in grams.
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