Pyridine is a weak base that is used in the manufacture of pesticides and plastic resins. It is also a component of cigarette smoke. Pyridine ionizes in water as follows:

Question

C5H5N + H2O<-->C5H5NH+ + OH-

The pKb of pyridine is 8.75. What is the pH of a 0.190 M solution of pyridine?

Answer 1

pKb = -log Kb
-8.75 = log Kb
Solve for Kb.

........BN + H2O ==> BNH^+ + OH^-
I......0.190..........0.......0
C.......-x............x........x
E......0.190-x........x........x

Substitute the E line into the Kb expression and solve for x = OH^-, then convert to pH.