AP Chemistry Questions on the Common Ion Effect and Ksp

📚 Quick Study Guide

• ⚖️ The Common Ion Effect is 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 direct consequence of Le Chatelier's Principle. Adding a common ion shifts the equilibrium towards the solid salt, reducing its solubility.
• 🔢 The solubility product constant, $K_{sp}$, represents the equilibrium constant for the dissolution of a solid substance into an aqueous solution.
• 📝 For a salt like $AgCl(s)$, the dissolution equilibrium is: $AgCl(s) \rightleftharpoons Ag^+(aq) + Cl^-(aq)$, and $K_{sp} = [Ag^+][Cl^-]$.
• 💡 When calculating solubility in the presence of a common ion, set up an ICE table (Initial, Change, Equilibrium) to determine the equilibrium concentrations.
• 🌡️ Remember that $K_{sp}$ is temperature-dependent.
• 📌 A smaller $K_{sp}$ value indicates lower solubility.

🧪 Practice Quiz

1. Question 1: The solubility of $AgCl$ in pure water is $1.3 \times 10^{-5}$ M. What is the $K_{sp}$ of $AgCl$?
   1. $1.3 \times 10^{-5}$
   2. $2.6 \times 10^{-5}$
   3. $1.7 \times 10^{-10}$
   4. $6.5 \times 10^{-6}$
2. Question 2: What is the solubility of $AgCl$ in a $0.1$ M $NaCl$ solution, given that the $K_{sp}$ of $AgCl$ is $1.8 \times 10^{-10}$?
   1. $1.8 \times 10^{-9}$ M
   2. $1.8 \times 10^{-10}$ M
   3. $1.34 \times 10^{-5}$ M
   4. $9.0 \times 10^{-10}$ M
3. Question 3: Which of the following salts will have the lowest molar solubility in a $0.2$ M solution of $Na_2CO_3$? ($K_{sp}$ values are given in parentheses.)
   1. $Ag_2CO_3$ ($8.1 \times 10^{-12}$)
   2. $BaCO_3$ ($2.6 \times 10^{-9}$)
   3. $CaCO_3$ ($3.4 \times 10^{-9}$)
   4. $MgCO_3$ ($6.8 \times 10^{-6}$)
4. Question 4: The $K_{sp}$ of $PbCl_2$ is $1.6 \times 10^{-5}$. What is the molar solubility of $PbCl_2$ in pure water?
   1. $1.6 \times 10^{-5}$ M
   2. $2.5 \times 10^{-3}$ M
   3. $1.6 \times 10^{-2}$ M
   4. $0.016$ M
5. Question 5: Calculate the molar solubility of $PbCl_2$ in a $0.1$ M $KCl$ solution, given that the $K_{sp}$ of $PbCl_2$ is $1.6 \times 10^{-5}$.
   1. $1.6 \times 10^{-5}$ M
   2. $4.0 \times 10^{-4}$ M
   3. $8.0 \times 10^{-4}$ M
   4. $1.26 \times 10^{-2}$ M
6. Question 6: Which of the following statements is true regarding the common ion effect?
   1. It increases the solubility of a salt.
   2. It decreases the solubility of a salt.
   3. It has no effect on the solubility of a salt.
   4. It only affects salts with a $K_{sp}$ greater than 1.
7. Question 7: What is the silver ion concentration, $[Ag^+]$, in a saturated solution of $Ag_2CrO_4$ containing $0.1$ M $K_2CrO_4$? ($K_{sp}$ of $Ag_2CrO_4 = 1.1 \times 10^{-12}$)
   1. $1.1 \times 10^{-11}$ M
   2. $1.05 \times 10^{-6}$ M
   3. $3.32 \times 10^{-6}$ M
   4. $5.5 \times 10^{-12}$ M