Question

You need to produce a buffer solution that has a pH of 5.00. You already have a solution that contains 10. mmolmmol (millimoles) of acetic acid. How many millimoles of acetate (the conjugate base of acetic acid) will you need to add to this solution

Answer 1

Answer : The  millimoles of acetate need to add to this solution will be, 18.2 mmol

Explanation :

For acetic acid, $pK_a=4.74$

Moles of of acetic acid = 10 mmol

pH = 5.00

Using Henderson Hesselbach equation :

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

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

$5.00=4.74+\log (\frac{Salt}{10})$

$Salt=18.2mmol$

Thus, the millimoles of acetate need to add to this solution will be, 18.2 mmol