What is the pH of a 0.10 M solution of C5H5NHCl

Answer 1

C5H5NHCl is the salt of a weak base, pyridine (C5H5N) plus a strong acid, HCl. Thus, a solution of this salt will have a pH <7 (acidic). We will find the pH by looking at the hydrolysis of the conjugate acid.

C5H5NH⁺ + H2O ==> C5H5N + H⁺

Now we need the Ka for C5H5NH⁺ which I looked up and found to be 5.6x10-6

Ka = [C5H5N][H⁺] / [C5H5NH⁺]

5.6x10-6 = (x)(x) / 0.10

x² = 5.6x10^-7

x = 7.48x10^-4 M = [H⁺]

pH = -log [H⁺]

pH = 3.13