In a solution of acetic acid, sodium acetate is added, then its pH value

Options

A. Decreases
B. Increases
C. Remains unchanged
D. (a) & (b) both are correct

Explanation

To determine the pH value of a solution of acetic acid when sodium acetate is added, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Components**:
- Acetic acid (CH₃COOH) is a weak acid that partially dissociates in water:
\[ \text{CH}_3\text{COOH} \rightleftharpoons \text{CH}_3\text{COO}^- + \text{H}^+ \]
- Sodium acetate (CH₃COONa) is a salt that dissociates completely in water to give acetate ions (CH₃COO⁻) and sodium ions (Na⁺):
\[ \text{CH}_3\text{COONa} \rightarrow \text{CH}_3\text{COO}^- + \text{Na}^+ \]

2. **Common Ion Effect**:
- When sodium acetate is added to the acetic acid solution, the concentration of acetate ions (CH₃COO⁻) increases. This is known as the common ion effect.
- The presence of additional acetate ions shifts the equilibrium of the dissociation of acetic acid to the left:
\[ \text{CH}_3\text{COOH} \rightleftharpoons \text{CH}_3\text{COO}^- + \text{H}^+ \]
- As a result, the concentration of hydrogen ions (H⁺) decreases.

3. **Effect on pH**:
- Since pH is inversely related to the concentration of hydrogen ions, a decrease in H⁺ concentration will lead to an increase in pH.
- The relationship between pH and H⁺ concentration is given by:
\[ \text{pH} = -\log[\text{H}^+] \]

4. **Conclusion**:
- Therefore, when sodium acetate is added to the acetic acid solution, the pH of the solution will increase due to the common ion effect, which reduces the concentration of H⁺ ions.

### Final Answer:
The pH value of the solution will increase when sodium acetate is added to a solution of acetic acid.

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