0.100 mol·L-1 NaAc solution. what is the pH?

Answer 1

NaAc = sodium acetate = CH3COONa

This is the salt formed from a strong base (NaOH) and a weak acid (acetic acid, CH3COOH, HAc)

The pH of the solution will be alkaline (pH > 7). To determine pH, look at hydrolysis of the acetate anion..

Ac^- + H₂O ==> HAc + OH^-

The Ka for HAc = 1.8x10^-5, so the Kb for Ac^- = 1x10^-14/1.8.10^-5 = 5.5x10^-10

Kb = 5.5x10^-10 = [HAc][OH^-][Ac^-] = (x)(x)/0.1

x² = 5.5x10^-11

x = 7.4x10^-6 = [OH^-]

pOH = 5.1

pH = 8.9