buffer system equilibrium

Question

5. A buffered system of HC2H3O2/NaC2H3O2 by combining 20.0 mL of 0.60 M HC2H3O2 and

20.0 mL of 0.60 M NaC2H3O2. The Ka of HC2H3O2 is 1.80x10-5, pKa = 4.74.

Answer 1

Since the volumes of the acid and salt solution are equal (both 20 mL)

The Henderson-Hasselbalch equation will give the pH of the buffer solution

pH = pK_a + log ( concentration of acetate ion / concentration of acid )

pH = 4.74 + log (.6 / .6) = 4.74