Question #4f8a7

The indicator is simply a LARGE, WEAK, organic acid, whose conjugate base/conjugate acid forms are readily differentiated by their different colours.

Personally, I find titrations with phenolphthalein excellent with respect to finding the stoichiometric endpoint of a reaction. A stoichiometric endpoint should be reached when you add approx. #0.01*mL# of titrant, that is ONE DROP from a burette, and when titrating an acid with base, the endpoint is easy to vizualize (i.e. colourless to slightly pink with one drop; this is easier to vizualize that yellow to blue or vice versa or pink to colourless).

At, or about the endpoint the colour of the solution, which is expressed by the indicator is VERY sensitive to addition of acid of base, because a few drops added cause such a large rise (or decrease) in solution #pH#. Are we clear on this?

The precipitous increase in solution #pH# as observed on the graph CLEARLY occurs within a narrow range of titrant volume........If you are not following what I argue, ask again, and someone will help you.