Examples of the Common Ion Effect in Buffer Solutions

📚 Quick Study Guide

• 🧪 The Common Ion Effect: The decrease in solubility of a salt when one of its ions is already present in the solution.
• ⚖️ Buffers: Solutions that resist changes in pH upon addition of small amounts of acid or base. They consist of a weak acid and its conjugate base (or a weak base and its conjugate acid).
• 📝 Henderson-Hasselbalch Equation: Used to calculate the pH of a buffer solution: $pH = pK_a + log(\frac{[A^-]}{[HA]})$ where $A^-$ is the conjugate base and $HA$ is the weak acid.
• ➕ The common ion effect influences the buffer's capacity and shifts the equilibrium according to Le Chatelier's principle. Adding a common ion will shift the equilibrium to reduce the concentration of that ion.
• 🔢 When calculating pH changes due to the common ion effect, consider the initial concentrations, the changes due to reaction, and the equilibrium concentrations using an ICE table (Initial, Change, Equilibrium).

🧪 Practice Quiz

1. Which of the following best describes the common ion effect in buffer solutions?
   1. The increase in pH when a common ion is added.
   2. The decrease in pH when a common ion is added.
   3. The suppression of ionization of a weak electrolyte by the presence of a common ion.
   4. The increase in the solubility of a salt when a common ion is added.
2. A buffer solution contains 0.1 M acetic acid ($CH_3COOH$) and 0.1 M sodium acetate ($CH_3COONa$). What happens to the pH if you add sodium acetate?
   1. The pH increases.
   2. The pH decreases.
   3. The pH remains the same.
   4. The pH becomes neutral.
3. Which of the following pairs can form a buffer solution?
   1. HCl and NaCl
   2. NaOH and NaCl
   3. $NH_3$ and $NH_4Cl$
   4. $HNO_3$ and $KNO_3$
4. What is the main function of a buffer solution?
   1. To completely neutralize acids.
   2. To completely neutralize bases.
   3. To resist changes in pH upon addition of small amounts of acid or base.
   4. To increase the pH of a solution.
5. What does the Henderson-Hasselbalch equation allow you to calculate?
   1. The concentration of a strong acid.
   2. The concentration of a strong base.
   3. The pH of a buffer solution.
   4. The pOH of a buffer solution.
6. In a buffer solution of formic acid ($HCOOH$) and sodium formate ($HCOONa$), what is the common ion?
   1. $H^+$
   2. $Na^+$
   3. $HCOO^-$
   4. $OH^-$
7. If you add a strong acid to a buffer solution, which component of the buffer will react with the acid?
   1. The weak acid.
   2. The conjugate base.
   3. The water.
   4. The salt.