Question

If you mixed 5.50 mL of the acidic solution with 6.79 mL of the basic solution, what should be the pH of the resulting solution? Report your answer with 3 decimal places. Note: The pKa for acetic acid is 4.757. The activity coefficients for acetic acid and the acetate ion are 1.000 and 0.775, respectively, in a solution with an ionic strength of 0.10 M.

Answer 1

Answer : The  pH of the resulting solution is 4.6

Explanation : Given,

$pK_a=4.757$

Activity coefficient for acetic acid = 1.000

Activity coefficient for acetate ion = 0.775

Ionic strength = 0.10 M

To calculate the pH of resulting solution we are  using Henderson Hesselbach equation :

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

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

$pH=4.757+\log (\frac{0.775\times 0.10}{1.000\times 0.10})$

$pH=4.6$

Thus, the pH of the resulting solution is 4.6