how to solve this question

Question

how many moles each of sodium acetate and acetic would you add to make a 2L solution of 0.04M acetate/acetic acid buffer

Answer 1

The answer to this will depend on the desired pH of the final buffer solution. For example, let us assume you want the final pH to be 4.8. Then we can use the Henderson-Hasselbalch equation where

pH = pKa + log [NaAc]/[HAc] where NaAc is sodium acetate and HAc is acetic acid. We can use a pKa of 4.8 for HAc (look it up in a table of Ka or pKa values) and solve for the ratio of NaAc/HAc

4.8 = 4.8 + log [NaAc]/[HAc]

log [NaAc]/[HAc] = 0

[NaAc]/[HAc] = 1 (since log 1 = 0)

To prepare 2 liters of 0.04 M acetate buffer, you would need 2 L x 0.04 mol/L = 0.08 moles acetate

Since the ratio of NaAc : HAc is 1:1 you would need 0.04 moles NaAc and 0.04 moles HAc