Question

What is the approximate pH of a 0.1 M solution of acetic acid and 0.01 M Sodium acetate (pKa of acetic acid is 4.5)?

Select one:

a. 3.5

b. 4.5

c. 5.5

d. 6.5

e. Cannot determine from the information given.

Answer 1

Answer - 3.5

Acetic acid in the aqueous solution dissociates into the acetate ion and hydrogen ions and sodium acetate in the aqueous solution dissociates into acetate ions and sodium ions. If sodium acetate and acetic acid both are present together in solution,causes the repression of the dissociation of acids,known as common ion effect.This is represented by the Henderson Hasselbalch equation.

By applying the Henderson Hasselbalch equation -

pH = pKA - log [concentration of acid /concentration of base]

= 4.5 - log [0.1M /0.01M]

= 4.5 - log [10]

= 4.5 -1 = 3.5