What is the pH of a buffer solution that is 0.59 M pyridine and 0.30 M pyridinium bromide? (Assume the value of Kw is 1.0 10-14.)

pH = 5.54

Explanation:

We can think of the pyridinium cation as a weak acid (of pKa 5.25), and of pyridine as its conjugate base. As such, we can use the Henderson-Hasselbach equation to solve this problem:

pH = pKa + log ([Pyridine]/[Pyridinium])

pH = 5.25 + log (0.59/0.30)

pH = 5.25 + 0.29

pH = 5.54