[treadlightly]

Hello all!

I have one question about a problem concerning the Henderson-Hasselbalch equation:
I'm mixing 100 milliliters of 1M Acetic acid (HOAC) (Pka=4.76) with 101 mL of 1M KOH in a flask and then adjusting the volume to 1 liter with water.
So basically, I have 0.1 mol of acetic acid and 0.101 mol of KOH. I'm trying to calculate pH.

I tried doing it the regular way, but then I realize that all of my weak acid has been neutralized. I'm not given a PKb so I can't do H-H in terms of the base. I'm left with,
pH = PKa + log (.10 mol OAc-/0.00 mol HOAC), which doesn't make sense because I'm dividing by zero. What can I do next?

[treadlightly]

So I went ahead and did the problem without using henderson hasselbalch. I just used the concentration of KOH I had after the neutralization, which is .001M and calculated pOH from that, which is 3. Then I used that to find pH, which would be 11. Could someone verify my answer, please?

[Borek]

Reasonably correct, this is basically a limiting reagent problem.

To be exact you should take into account fact that CH₃COO^- is a weak base:

CH₃COO^- + H₂O CH₃COOH + OH^-

that would slightly shift the OH^- concentration. But the change would be so small it can be safely ignored.