Question

Calculate the pH of buffer solution containing \(0.12 \text{ M}\) weak acid and \(0.48 \text{ M}\) of its salt with strong base if \(pK_a\) is 3.82 .

• A. 5.31
• B. 2.67
• C. 3.72
• D. 4.42

Hint:

Buffer rule: If salt > acid → pH > pK$_a$.

Answer 1

The Correct Option is D

Concept: Henderson–Hasselbalch equation \[ \text{pH} = pK_a + \log \frac{[\text{Salt}]}{[\text{Acid}]} \]

Step 1: Substitute values \[ \text{pH} = 3.82 + \log \left(\frac{0.48}{0.12}\right) \]

Step 2: Simplify ratio \[ \frac{0.48}{0.12} = 4 \] \[ \log 4 = 0.602 \]

Step 3: Calculate \[ \text{pH} = 3.82 + 0.60 = 4.42 \] Conclusion: \[ \text{pH} = 4.42 \]