Common Ion Effect Examples: Buffers and Solubility

📚 Quick Study Guide

• ⚛️ The common ion effect describes the decrease in solubility of a sparingly soluble salt if a soluble salt containing a common ion is added to the solution.
• ⚖️ For solubility problems, use an ICE table to calculate the new solubility with the common ion present. Remember to include the initial concentration of the common ion.
• 🧪 Buffers resist changes in pH when small amounts of acid or base are added. They consist of a weak acid and its conjugate base (or a weak base and its conjugate acid).
• ⚗️ Henderson-Hasselbalch Equation: $pH = pK_a + log(\frac{[A^-]}{[HA]})$ where $[A^-]$ is the concentration of the conjugate base and $[HA]$ is the concentration of the weak acid.
• 💡 The common ion effect is essential for buffer action. The presence of both the weak acid and its conjugate base in the buffer solution, a common ion situation, helps to neutralize added acid or base.

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 pH of a solution due to a common ion.
   4. The decrease in pH of a solution due to a common ion.

2. Which of the following is an example of a buffer solution?

   1. HCl (strong acid)
   2. NaOH (strong base)
   3. $CH_3COOH$ (weak acid) and $CH_3COONa$ (its salt)
   4. NaCl (neutral salt)

3. What is the Henderson-Hasselbalch equation used to calculate?

   1. Solubility of a salt
   2. pH of a buffer solution
   3. Concentration of a strong acid
   4. Concentration of a strong base

4. If the solubility of $AgCl$ in pure water is $1.3 \times 10^{-5}$ M, what will happen to its solubility if $NaCl$ is added to the solution?

   1. Solubility will increase.
   2. Solubility will decrease.
   3. Solubility will remain the same.
   4. Solubility will initially increase and then decrease.

5. A buffer solution contains 0.1 M of acetic acid ($CH_3COOH$, $K_a = 1.8 \times 10^{-5}$) and 0.1 M of sodium acetate ($CH_3COONa$). What is the pH of the buffer?

   1. 2.87
   2. 4.74
   3. 7.00
   4. 9.13

6. Which of the following statements about buffers is true?

   1. Buffers are most effective when the concentrations of the weak acid and its conjugate base are equal.
   2. Buffers are only effective against the addition of acids.
   3. Buffers are only effective against the addition of bases.
   4. Buffers are made of strong acids and strong bases.

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

   1. Increases the pH.
   2. Decreases the pH.
   3. No effect on the pH.
   4. Neutralizes the $NH_3$.