Question

What will be pH of aqueous salt solution of AB if pKa of weak acid HA is 4 and pKb of weak acid BOH is 5?

• A. 5
• B. 6.5
• C. 7.5
• D. 11.5

Hint:

For salts of weak acids and bases, the pH can be determined using the formula: \(\text{pH} = 7 + \frac{1}{2}(\text{pKa} + \text{pKb})\).

Answer 1

The Correct Option is C

The pH of an aqueous salt solution can be determined by considering the acid dissociation constant (Ka) and base dissociation constant (Kb). We can use the following relation: \[ \text{pH} = 7 + \frac{1}{2}(\text{pKa} + \text{pKb}) \] Given: - pKa of HA = 4 - pKb of BOH = 5 Thus, \[ \text{pH} = 7 + \frac{1}{2}(4 + 5) \] \[ \text{pH} = 7 + \frac{1}{2}(9) = 7 + 4.5 = 7.5 \] Thus, the pH of the solution is 7.5.