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 ([Salt])/([Acid])`

`pH=pK_a+\log ([CH_3COONa])/([CH_3COOH])`

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

`4.76=pK_a+\log ((0.10)/(0.10))`

`pK_a=4.76`

Therefore, the pKa for acetic acid is, 4.76