Question
At 298 K, a certain buffer solution contains equal concentrations of X^ - and HX, K_b for X^ - is 10^ -10 . What is the pH of this buffer solution ?
NEET
Chemistry
Ionic Equilibrium
2026
NEET 2026 (Cancelled)
NEET Chemistry Question (2026) — Solution
Options
- A. 2
- B. 4
- C. 6
- D. 10
Answer
B. 4
Step-by-step solution
Given K_b for X^ - = 10^ -10 . For a conjugate acid-base pair at 298 K, K_a K_b = K_w = 10^ -14 . K_a = 10^ -14 10^ -10 = 10^ -4 The pK_a of the weak acid HX is: pK_a = - (K_a) = - (10^ -4 ) = 4 Using the Henderson-Hasselbalch equation for an acidic buffer: pH = pK_a + ( [X^ - ] [HX] ) Since the concentrations of X^ - and HX are equal, [X^ - ] = [HX]. pH = 4 + (1) = 4 + 0 = 4 Answer: 4
Related: Chemistry — Ionic Equilibrium · All PYQ Banks