# Why should colorimetric titration of a weak acid with a weak base not be done in laboratory? [closed]

Why should colorimetric titration of weak acid with a weak base (or vice versa) not be done in laboratory?

How can I draw a pH graph for this?

## closed as off-topic by Loong♦, ringo, ron, Freddy, EkaMay 2 '15 at 4:21

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• Here is a paper with titration curves of weak acids with weak bases. – Karsten Theis Mar 5 at 15:42

Drawing the titration curve is hard, because you generate a buffer system which buffers against acids and bases at the same time. Around the equivalence point the buffer system works equally well against acids and bases (assuming their $\text{p}K_\text{a}$ values are the same), resulting in a slow rise of the pH. You don't get the usual "jump" in the curve at the equivalence point, which makes it hard to detect the actual equivalence point (your indicator should fulfill $\text{p}K_\text{a}^\text{Ind} = \text{pH}_\text{equiv.}$, which is highly unlikely).