Question

. A solution of 0.10 M acetic acid and 0.10 M sodium acetate has a pH of 4.76. Determine the pKaof acetic acid. What is the pKafor acetic acid?

Answer 1

Answer : The  pKa for acetic acid is, 4.76

Explanation : Given,

$pH=4.76$

Concentration of acetic acid (acid) = 0.10 M

Concentration of sodium acetate (salt) = 0.10 M

The equilibrium reaction will be:

$CH_3COOH+NaOH\rightleftharpoons CH_3COONa+H_2O$

Using Henderson Hesselbach equation :

$pH=pK_a+\log \frac{[Salt]}{[Acid]}$

$pH=pK_a+\log \frac{[CH_3COONa]}{[CH_3COOH]}$

Now put all the given values in this expression, we get:

$4.76=pK_a+\log (\frac{0.10}{0.10})$

$pK_a=4.76$

Therefore, the pKa for acetic acid is, 4.76