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. So from this equation we see that if this is true, only then will the PH equal to the PKA. So once again, from this previous graph, we basically describe the Titration curve for the buffer system in which we have acetic acid as that acid and acetate ion as the conjugate base. Now, the PKA value of acetic acid is 4.75.