HELP ASAP PLEASE!!!!

Question

18.Calculate the pH of a buffer solution that is 0.195 M in CH₃CO₂H and

      0.125 M  NaCH₃CO₂ ?

Answer 1

We will use the Henderson Hasselbalch Equation:

pH - pKa + log(B/A)

Ka of acetic acid (Ch₃CO₂H) is 1.8 x 10^-5)

Let's first determine the pKa:

pKa = -log(1.8 x 10^-5) = 4.74

Now let's look at amounts of weak acids and conjugate bases. Comparing 0.195 WA to 0.125 WB, we see that we have a higher amount of WA. This means that we should have a more acidic buffer, which is indicated a pH lower than the pKa. Let us see if this works.

pH = -log(1.8 x 10^-5) + log(0.125 M/0.195) = 4.55

Yes. This checks out so the buffer is 4.55.