Question

What is the pH of 0.1M acetic acid solution, pKa = 4.76?

What is the pH of 0.1M acetic acid solution, pKa = 4.76? What is the pH after enough sodium acetate has been added to make the solution 0.1M with respect to the salt?

Answer

Ka = 1.74E-5

. .CH3COOH <---> CH3COO- + H+

I. . .0.1. . . . . . .. . .. . .. . . .0. . . . . . 0

E. .0.1-x. . . . . . . . ....... . . .x. . . . . . .x

ka = [CH3COO-][H+] / [CH3COOH]

1.74E-5 = x^2 / 0.1 - x

x = 0.00131 M = [H+]

pH = -log[H+] = 2.88

To make the sodium acetate 0.1 M with respect to that salt, you would need 0.1 M sodium acetate. This will make the ratio of acid/conjugate base 1:1.

pH = pKa + log(A-/HA)

When the ratio is 1:1, then the pH = pKa. So the pH = 4.76.

Jun 16 at 15:44