Question

Solution of 0.1 N \(NH_4OH\) and 0.1 N \(NH_4Cl\) has pH 9.25. Then p\(K_b\) of \(NH_4OH\) is :

• A. 9.25
• B. 4.75
• C. 3.75
• D. 8.25

Hint:

For equal buffer components, pH = pKa or pOH = pKb.

Answer 1

The Correct Option is B

Concept: Buffer formula: \[ \text{pOH} = pK_b + \log \frac{[\text{salt}]}{[\text{base}]} \]

Step 1: Given.
Equal concentrations $\Rightarrow$ log term = 0 \[ \text{pOH} = pK_b \]

Step 2: Convert pH to pOH.
\[ pOH = 14 - 9.25 = 4.75 \] \[ \Rightarrow pK_b = 4.75 \]