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:

Question

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

Quizplus · Accepted Answer

According to the dissociation equation for pyridine, pyridine + H2O <=> pyridine+ + OH- the equilibrium expression is: K_b = [pyridine+][OH-]/[pyridine] Since we are given the value of K_b and the initial concentration of pyridine, we can use the quadratic equation to solve for [OH-]: K_b = [pyridine+][OH-]/[pyridine] 1.9 × 10^-9 = x^2/([pyridine]-x) Assuming x << [pyridine], we can simplify the expression: 1.9 × 10^-9 = x^2/[pyridine] x = sqrt(K_b[pyridine]) x = sqrt(1.9 × 10^-9 * 0.30) = 1.73 × 10^-5 Therefore, [OH-] = 1.73 × 10^-5 M The pH is given by: pH = 14 - pOH = 14 - (-log[OH-]) = 9.38 Therefore, the answer is C.

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