Titrations in Polyprotic Systems

The slope of the titration curve is minimum at VJ2 when pH = p a The slope is steepest at the equivalence point. 

Before delving into titration curves for diprotic systems, you should realize that there are two buffer pairs derived from the acid H2A. H2A and HA constitute one buffer pair and HA and A constitute a second pair. For the acid H2A, there are two Henderson-Hasselbalch equations, both of which are always true. If you happen 

All Henderson-Hasselbalch equations are always true for a solution at equilibrium. 

Point A has the same pH in all three cases. It is the pH of the acid H2A, which is treated as a monoprotic acid with pATa = pATi = 4.00 and formal concentration F. 

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