AP Chemistry Questions on Ksp: Exam Preparation

🧪 Quick Study Guide

• ⚖️ Solubility Product (Ksp): Represents the equilibrium constant for the dissolution of a sparingly soluble ionic compound. A higher Ksp indicates greater solubility.
• 📝 Solubility Equilibrium: The dynamic equilibrium between a solid ionic compound and its ions in a saturated solution. For example, for $AgCl(s) \rightleftharpoons Ag^+(aq) + Cl^-(aq)$, $K_{sp} = [Ag^+][Cl^-]$.
• ➕ Calculating Ksp from Solubility: If the solubility of a compound is 's' (in mol/L), you can determine the ion concentrations at equilibrium and then calculate Ksp. For example, if $AgCl$'s solubility is 's', then $[Ag^+] = s$ and $[Cl^-] = s$, so $K_{sp} = s^2$.
• ➗ Calculating Solubility from Ksp: Given the Ksp value, you can calculate the solubility ('s') of the compound by setting up an ICE table and solving for 's'.
• 💡 Common Ion Effect: The solubility of a sparingly soluble salt is reduced when a soluble compound containing a common ion is added to the solution.
• 🌡️ Temperature Dependence: Ksp values are temperature-dependent. Solubility generally increases with increasing temperature for most (but not all) ionic compounds.
• 🧮 Q vs. Ksp:
  • $Q < K_{sp}$: Unsaturated solution; more solid can dissolve.
  • $Q = K_{sp}$: Saturated solution; the system is at equilibrium.
  • $Q > K_{sp}$: Supersaturated solution; precipitation will occur until $Q = K_{sp}$.

Practice Quiz

1. Which of the following expressions represents the solubility product constant, Ksp, for $Ag_2CO_3(s)$?
   1. $K_{sp} = [Ag^+][CO_3^{2-}]$
   2. $K_{sp} = [Ag^+]^2[CO_3^{2-}]$
   3. $K_{sp} = [Ag^+][CO_3^{2-}]^2$
   4. $K_{sp} = 2[Ag^+][CO_3^{2-}]$
2. The Ksp of $PbCl_2$ is $1.6 x 10^{-5}$. What is the molar solubility of $PbCl_2$ in water?
   1. $1.6 x 10^{-5} M$
   2. $2.5 x 10^{-3} M$
   3. $1.6 x 10^{-2} M$
   4. $0.016 M$
3. The solubility of $CaF_2$ in water is $3.3 x 10^{-4} M$. Calculate the Ksp for $CaF_2$.
   1. $3.6 x 10^{-11}$
   2. $4.3 x 10^{-8}$
   3. $1.1 x 10^{-7}$
   4. $1.4 x 10^{-10}$
4. What is the effect of adding $NaCl$ to a saturated solution of $AgCl$?
   1. The solubility of $AgCl$ increases.
   2. The solubility of $AgCl$ decreases.
   3. The solubility of $AgCl$ remains the same.
   4. $AgCl$ precipitates completely.
5. For $BaSO_4$, $Ksp = 1.1 x 10^{-10}$. What is the concentration of $Ba^{2+}$ in a saturated solution of $BaSO_4$?
   1. $1.1 x 10^{-10} M$
   2. $1.05 x 10^{-5} M$
   3. $2.2 x 10^{-10} M$
   4. $1.0 x 10^{-10} M$
6. Which of the following salts has the lowest molar solubility given their Ksp values?
   1. $AgCl$, $Ksp = 1.8 x 10^{-10}$
   2. $PbCl_2$, $Ksp = 1.6 x 10^{-5}$
   3. $Ag_2CrO_4$, $Ksp = 1.1 x 10^{-12}$
   4. $CaF_2$, $Ksp = 3.9 x 10^{-11}$
7. A solution contains $0.01 M$ $Pb^{2+}$ ions. If $KI$ is added, what concentration of $I^-$ is required to initiate precipitation of $PbI_2$? ($Ksp$ of $PbI_2 = 7.1 x 10^{-9}$)
   1. $7.1 x 10^{-7} M$
   2. $8.4 x 10^{-5} M$
   3. $2.7 x 10^{-4} M$
   4. $0.001 M$