Question

Equal volumes of 0.5 N acetic acid and 0.5 N sodium acetate are mixed. What is the pH of resultant solution?
(\( \text{p}K_a \) of acetic acid = 4.75)

• A. 4.85
• B. 4.65
• C. 4.75
• D. 7.0

Hint:

If concentrations of acid and conjugate base are equal, then \( \text{pH} = \text{p}K_a \).

Answer 1

The Correct Option is C

This is a buffer solution of a weak acid and its salt in equal concentrations.
Use Henderson-Hasselbalch equation:
\[ \text{pH} = \text{p}K_a + \log \left( \frac{[\text{Salt}]}{[\text{Acid}]} \right) = 4.75 + \log(1) = 4.75 \]