Short Answer

Salt hydrolysis is the reaction of a salt with water to produce an acidic or basic solution. When salts dissolve in water, they may react with water molecules depending on the ions present, changing the pH of the solution.

For example, sodium acetate (CH₃COONa) hydrolyzes in water to produce a basic solution, while ammonium chloride (NH₄Cl) hydrolyzes to produce an acidic solution. The nature of the salt and the strengths of its parent acid and base determine the type of hydrolysis.

Detailed Explanation :

Salt Hydrolysis

Salt hydrolysis is a chemical process in which the ions of a salt react with water, resulting in a change in the pH of the solution. This reaction occurs when a salt is formed from a strong acid and a weak base or a weak acid and a strong base, or in some cases, both weak. Salt hydrolysis explains why some salt solutions are acidic, some are basic, and others are neutral.

Types of Salt Hydrolysis

1. Salt from Strong Acid and Weak Base

• These salts produce an acidic solution in water.
• Example: Ammonium chloride (NH₄Cl)
• Hydrolysis reaction:
  NH₄⁺ + H₂O → NH₄OH + H⁺
• The NH₄⁺ ion reacts with water, releasing H⁺ ions, making the solution acidic.
• Explanation: The parent acid (HCl) is strong and does not hydrolyze, while the weak base (NH₃) forms NH₄⁺ ions that hydrolyze.

2. Salt from Weak Acid and Strong Base

• These salts produce a basic solution in water.
• Example: Sodium acetate (CH₃COONa)
• Hydrolysis reaction:
  CH₃COO⁻ + H₂O → CH₃COOH + OH⁻
• The CH₃COO⁻ ion reacts with water to produce OH⁻ ions, making the solution basic.
• Explanation: The parent acid (CH₃COOH) is weak, while the base (NaOH) is strong and does not hydrolyze.

3. Salt from Strong Acid and Strong Base

• These salts do not hydrolyze and produce a neutral solution.
• Example: Sodium chloride (NaCl)
• Neither Na⁺ nor Cl⁻ reacts with water, so the pH remains neutral (≈ 7).

4. Salt from Weak Acid and Weak Base

• These salts hydrolyze partially, producing a solution that can be slightly acidic or basic depending on relative strengths.
• Example: Ammonium acetate (CH₃COONH₄)
• Both ions hydrolyze:
  CH₃COO⁻ + H₂O → CH₃COOH + OH⁻
  NH₄⁺ + H₂O → NH₄OH + H⁺
• The solution pH depends on Ka and Kb values of the parent acid and base.

Factors Affecting Salt Hydrolysis

1. Strength of Parent Acid and Base

• Strong acid + weak base → acidic solution
• Weak acid + strong base → basic solution
• Strong acid + strong base → neutral solution
• Weak acid + weak base → depends on relative strengths

2. Concentration of Salt

• Higher concentration increases hydrolysis effect because more ions interact with water.

3. Temperature

• Higher temperatures may increase hydrolysis rate but do not change the type of solution (acidic/basic/neutral).

Applications of Salt Hydrolysis

1. Explaining pH of Salt Solutions

• Hydrolysis helps predict whether a salt solution will be acidic, basic, or neutral.

2. Industrial Chemistry

• Used in designing buffer solutions and controlling pH in chemical processes.

3. Environmental Chemistry

• Salt hydrolysis explains acidity in natural waters containing salts of weak acids or bases.

4. Laboratory Experiments

• Hydrolysis reactions are studied to understand acid-base equilibria.

Examples of Salt Hydrolysis in Everyday Life

1. NH₄Cl solution → acidic due to hydrolysis of NH₄⁺
2. Na₂CO₃ solution → basic due to hydrolysis of CO₃²⁻
3. NaCl solution → neutral, no hydrolysis
4. CH₃COONH₄ solution → slightly basic or acidic depending on Ka/Kb

These examples show how hydrolysis affects the nature of the solution.

Conclusion

Salt hydrolysis is the reaction of ions from a salt with water, resulting in an acidic, basic, or neutral solution depending on the strengths of the parent acid and base. Salts from strong acids and weak bases give acidic solutions, salts from weak acids and strong bases give basic solutions, and salts from strong acids and strong bases give neutral solutions. This concept is essential in chemistry, environmental science, industrial processes, and laboratory studies for predicting and controlling the pH of salt solutions.