AP Chemistry Questions on the Common Ion Effect

📚 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.
• ➗ To calculate the solubility of a salt in the presence of a common ion, set up an ICE table similar to solubility equilibrium problems.
• 📝 Remember that the initial concentration of the common ion must be included in the 'I' row of the ICE table.
• ➕ The solubility ($s$) represents the change in concentration of the ions from the sparingly soluble salt as it dissolves.
• 🧮 Use the $K_{sp}$ expression to solve for $s$: $K_{sp} = [M^{n+}]^m[X^{m-}]^n$, where $M$ is the cation, and $X$ is the anion.
• 🌡️ The common ion effect is an application of Le Chatelier's principle; adding a common ion shifts the equilibrium towards the undissolved salt.
• 💡 Approximations can often be made if the $K_{sp}$ value is small, simplifying the algebra: Assume $x$ is negligible compared to the initial concentration of the common ion.

🧪 Practice Quiz

1. What is the common ion effect?

   1. The increase in solubility of a salt due to a common ion.
   2. The decrease in solubility of a salt due to a common ion.
   3. The increase in the $K_{sp}$ value.
   4. The decrease in the $K_{sp}$ value.

2. Which of the following salts is least soluble in a 0.1 M solution of NaCl? Given: $K_{sp}$(AgCl) = $1.8 \times 10^{-10}$

   1. AgBr ($K_{sp} = 5.0 \times 10^{-13}$)
   2. AgI ($K_{sp} = 8.3 \times 10^{-17}$)
   3. AgCl ($K_{sp} = 1.8 \times 10^{-10}$)
   4. AgCN ($K_{sp} = 2.2 \times 10^{-12}$)

3. The solubility of $AgCl$ in pure water is $1.3 \times 10^{-5}$ M. What is the solubility of $AgCl$ in 0.10 M $NaCl$?

   1. $1.7 \times 10^{-9}$ M
   2. $1.3 \times 10^{-5}$ M
   3. $1.3 \times 10^{-6}$ M
   4. $1.8 \times 10^{-9}$ M

4. Which of the following statements is true regarding the common ion effect on the solubility of $Mg(OH)_2$ in a solution containing $NaOH$?

   1. The solubility of $Mg(OH)_2$ will increase.
   2. The solubility of $Mg(OH)_2$ will decrease.
   3. The solubility of $Mg(OH)_2$ will remain the same.
   4. The $K_{sp}$ of $Mg(OH)_2$ will increase.

5. What is the effect of adding $NH_4Cl$ to a saturated solution of $NH_3$?

   1. Increases the concentration of $OH^-$
   2. Decreases the concentration of $OH^-$
   3. No effect on the concentration of $OH^-$
   4. Increases the concentration of $NH_3$

6. Calculate the molar solubility of $BaSO_4$ ($K_{sp} = 1.1 \times 10^{-10}$) in 0.10 M $Na_2SO_4$ solution.

   1. $1.1 \times 10^{-9}$ M
   2. $1.1 \times 10^{-10}$ M
   3. $1.0 \times 10^{-5}$ M
   4. $1.1 \times 10^{-8}$ M

7. Which of the following will decrease the solubility of $Ag_2CrO_4$ in water?

   1. Adding $HNO_3$
   2. Adding $AgNO_3$
   3. Adding $NH_3$
   4. Adding $KCl$