NEET 2026 — Chemistry solution

NEET2026Chemistry

At 298K, a certain buffer solution contains equal concentrations of $X^{-}$ and HX, $K_{b}$ for $X^{-}$ is $1 0^{- 10}$ . What is the pH of this buffer solution?

A
10
B
4
C
2
D
6

Solution

For the conjugate pair, $K_{a} \times K_{b} = 1 0^{- 14}$ , so $K_{a} (H X) = 1 0^{- 14} /1 0^{- 10} = 1 0^{- 4}$ , giving $p K_{a} = 4$ .

By the Henderson–Hasselbalch equation,

$p H = p K_{a} + lo g \frac{[ X ^{-} ]}{[ H X ]} = 4 + lo g 1 = 4$ .

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