At what point in the concentration of the weak acid or conjugate base does the buffer solution stop resisting a PH change when strong acid is added ?

Question

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Answer 1

As an example, when acetate, Ac^- is the conjugate base, then
Ac^- + H^+ ==> HAc
Therefore, when Ac^- has been used up,[(HAc) = 0] there is nothing to inhibit the H^+. For all practical purposes, however, when (Ac^-) becomes very small there is very little buffering capacity.