Question

What is the pH of buffer solution containing \(10\) times higher molar concentration of weak base than the molar concentration of salt of weak base with strong acid at \(298\) K? (\(K_{b}\) of weak base \(=10^{-5}\))

• A. \(6\)
• B. \(4\)
• C. \(9\)
• D. \(10\)

Hint:

Use the basic buffer equation pOH equals pKb plus log of salt over base, then convert to pH.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept
For a basic buffer, \(\text{pOH}=\text{p}K_{b}+\log\dfrac{[\text{salt}]}{[\text{base}]}\).

Step 2: Substitute
\(K_{b}=10^{-5}\), so \(\text{p}K_{b}=5\). The base is 10 times the salt, so \(\dfrac{[\text{salt}]}{[\text{base}]}=\dfrac{1}{10}\) and \(\log\dfrac{1}{10}=-1\).

Step 3: Calculation
\(\text{pOH}=5-1=4\), so \(\text{pH}=14-4=10\) at 298 K.

Final Answer:
The pH of the buffer is 10. \[ \boxed{\text{(D) }10} \]