The Ka value for acetic acid, CH3COOH(aq) , is 1.8×10^−5 .

Question

Calculate the pH of a 3.00 M acetic acid solution.

Answer 1

Ka = [H⁺][Ac^-]/[HAc]

1.8x10^-5 = (x)(x)/3.00-x and assuming x is small relative to 3 M....

1.8x10^-5 = x²/3

x² = 5.4 x10^-5

x = 7.35x10^-3 M = [H+]

pH = -log [H+] = - log 7.35x10^-3

pH = 2.1