So we see that for this particular buffered system in which we use acetic acid and acetate ion for that buffered system, the greatest ability of this buffered system to resist a change in PH is when the PH is equal to 4.75. Now, what is the PKA of acetic acid? Well, if you look up the PKA value of acetic acid, it's 4.75. And that is not a coincidence, because if we go back to this equation and we plug in a PH of 4.75 and the PKA of 4.75, then we'll see that the PH is equal to the PKA only if the concentration of the base is equal to the concentration of that acid. That is, if this is equal to this, then this ratio is equal to one, and only then will log of one be equal to zero. And if this log is equal to zero, only then will the PH equal to the PKA.