What is Salt Hydrolysis? Chemistry Definition and Examples

📚 Quick Study Guide

• 🔍 Definition: Salt hydrolysis is the reaction of a salt with water to produce either an acidic or basic solution.
• 🧪 Ions Involved: The cation or anion of the salt reacts with water, or both can react.
• ⚖️ Salts from Strong Acids and Strong Bases: These salts do NOT undergo hydrolysis (e.g., NaCl).
• acidic or basic properties.
  • Cations from Weak Bases: (e.g., $NH_4^+$) produce acidic solutions.
  • Anions from Weak Acids: (e.g., $CH_3COO^-$) produce basic solutions.
• ➗ Hydrolysis Constant ($K_h$): Represents the equilibrium constant for the hydrolysis reaction.
• 📝 Important Equations:
  • For acidic hydrolysis: $K_h = \frac{K_w}{K_b}$
  • For basic hydrolysis: $K_h = \frac{K_w}{K_a}$
• 💡 Key Factors: The strength of the conjugate acid or base determines the extent of hydrolysis. A stronger conjugate implies greater hydrolysis.

Practice Quiz

1. Which of the following salts will produce a basic solution when dissolved in water?

   1. $NH_4Cl$
   2. $NaCl$
   3. $KCN$
   4. $FeCl_3$

2. What type of ion from a salt derived from a weak acid causes basic hydrolysis?

   1. Cation
   2. Anion
   3. Neutral molecule
   4. Hydronium ion

3. Which of the following solutions will NOT undergo hydrolysis?

   1. $Na_2CO_3$
   2. $KCl$
   3. $NH_4NO_3$
   4. $CH_3COONa$

4. If a salt $NaA$ is derived from a weak acid $HA$ with $K_a = 1.0 \times 10^{-5}$, what is the hydrolysis constant, $K_h$, for $A^-$?

   1. $1.0 \times 10^{-5}$
   2. $1.0 \times 10^{-9}$
   3. $1.0 \times 10^{-14}$
   4. $1.0 \times 10^{-7}$

5. Which of the following statements about salt hydrolysis is correct?

   1. Salts of strong acids and strong bases undergo hydrolysis extensively.
   2. Hydrolysis only occurs with salts containing transition metals.
   3. The pH of a solution of a salt that undergoes hydrolysis is always 7.
   4. Salts of weak acids produce basic solutions due to hydrolysis of the anion.

6. What is the effect of increasing the temperature on the hydrolysis of a salt?

   1. It always decreases the extent of hydrolysis.
   2. It always increases the extent of hydrolysis.
   3. It has no effect on the extent of hydrolysis.
   4. The effect depends on whether the hydrolysis is endothermic or exothermic.

7. Which of the following salts will produce an acidic solution?

   1. $NaCl$
   2. $NaCN$
   3. $NH_4Cl$
   4. $NaF$