Common Ion Effect Examples in Solubility Equilibria

📚 Quick Study Guide

• ⚖️ The Common Ion Effect describes the decrease in solubility of a sparingly soluble salt when a soluble salt containing a common ion is added to the solution.
• ⚗️ This effect is a specific case of Le Chatelier's principle. Adding a common ion shifts the equilibrium of the dissolution reaction back towards the solid, thus decreasing the solubility of the original salt.
• 🔢 Consider the solubility equilibrium of $AgCl(s) \rightleftharpoons Ag^+(aq) + Cl^-(aq)$. If we add $NaCl$, which contains the common ion $Cl^-$, the equilibrium shifts to the left, reducing the solubility of $AgCl$.
• 📝 The solubility product constant, $K_{sp}$, remains constant at a given temperature, even with the addition of a common ion. The concentrations of the ions at equilibrium will change, but their product will still equal $K_{sp}$.
• 💡 To calculate the new solubility, set up an ICE (Initial, Change, Equilibrium) table. Account for the initial concentration of the common ion.
• 🌡️ Remember that temperature affects solubility and thus $K_{sp}$. All calculations assume a constant temperature.

🧪 Practice Quiz

1. Which of the following describes the common ion effect?

   1. A) An increase in the solubility of a salt due to the presence of a common ion.
   2. B) A decrease in the solubility of a salt due to the presence of a common ion.
   3. C) No change in the solubility of a salt.
   4. D) The precipitation of a salt due to the absence of a common ion.

2. What happens to the solubility of $AgCl$ when $NaCl$ is added to the solution?

   1. A) Increases
   2. B) Decreases
   3. C) Stays the same
   4. D) Initially increases, then decreases

3. The solubility of $BaSO_4$ is affected by the addition of which of the following?

   1. A) $KCl$
   2. B) $NaNO_3$
   3. C) $BaCl_2$
   4. D) $LiBr$

4. What remains constant when a common ion is added to a solution of a sparingly soluble salt?

   1. A) Solubility
   2. B) Ionic concentrations
   3. C) $K_{sp}$
   4. D) Volume of the solution

5. Which of the following salts is least soluble in a 0.1 M solution of $NaCl$? (Given: $K_{sp}(AgCl) = 1.8 \times 10^{-10}$, $K_{sp}(AgBr) = 5.0 \times 10^{-13}$, $K_{sp}(AgI) = 8.3 \times 10^{-17}$)

   1. A) $AgCl$
   2. B) $AgBr$
   3. C) $AgI$
   4. D) All are equally soluble

6. If the solubility of $Mg(OH)_2$ in pure water is 's', what happens to 's' when $NaOH$ is added to the solution?

   1. A) 's' increases
   2. B) 's' decreases
   3. C) 's' remains the same
   4. D) 's' doubles

7. Which of the following is NOT an example of the common ion effect?

   1. A) Decreased solubility of $PbCl_2$ in the presence of $HCl$.
   2. B) Decreased solubility of $AgBr$ in the presence of $KBr$.
   3. C) Increased solubility of $CaF_2$ in the presence of $NaF$.
   4. D) Decreased solubility of $Fe(OH)_3$ in the presence of $NaOH$.