What is the pH of a 0.30 mol L^-1 pyridine solution that has K_b = 1.9 × 10^-9? The equation for the dissociation of pyridine is below: A)4.62 B)8.72 C)9.38 D)10.38

Question

Quizplus · Accepted Answer

Pyridine is a weak base and undergoes the following dissociation:
C5H5N + H2O ⇄ C5H5NH+ + OH-
The equilibrium constant for this reaction is given by:
KB = [C5H5NH+][OH-]/[C5H5N]
We are given KB = 1.9 × 10-9 and [C5H5N] = 0.30 M. The concentration of [OH-] can be calculated using the equilibrium constant expression:
1.9 × 10-9 = x2/0.30
x = [OH-] = 1.1 × 10-5 M
To calculate the pH, we use the relationship:
pH + pOH = 14
pH = 14 - pOH = 14 - (-log[OH-]) = 9.38
Therefore, the answer is C.

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