Question

Calculate the pH of buffer solution containing \(0.02\) M weak acid and \(0.04\) M its salt with a strong base.
[\(K_{a}=7.2\times 10^{-4}\)]

• A. \(3.14\)
• B. \(3.44\)
• C. \(3.76\)
• D. \(3.96\)

Hint:

Use the Henderson-Hasselbalch equation with pKa and the salt to acid ratio.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept
For an acidic buffer, \(\text{pH}=\text{p}K_a+\log\dfrac{[\text{Salt}]}{[\text{Acid}]}\).

Step 2: Find pKa
\(\text{p}K_a=-\log(7.2\times 10^{-4})=3.14\)

Step 3: Calculation
\(\log\dfrac{0.04}{0.02}=\log 2=0.301\)
\(\text{pH}=3.14+0.30=3.44\)

Step 4: Compare the options
This matches option (B).

Final Answer:
The pH of the buffer is 3.44. \[ \boxed{\text{(B) }3.44} \]