So once again, by adding acid to a buffered solution to a water solution that contains a buffered system, there is a much more gradual change of PH as seen in this box region. The question is, why does the PH change gradually? Well, because of what we said earlier. Because inside that buffered system, we have this acid, an equal concentration of its conjugate base. So if this is our acid, then the concentration of the conjugate base is exactly the same. And for this particular graph, the acid is once again acetic acid, and the conjugate base is the acetate ion.