titration curve 10 points !

1.
knowledge-san, it's "equivalence point".
it just indicates point where acid and base (in the reaction concerned) are in equal number of mole.
also, the slope does not necessaqrily to be infinity; the change in pH can be gradual. think about weak acid-weak base titration.

it's possible that end-point could not not be found on graph ---- end point is where indicator changes its color. thus, end-point is dependent on species of acid, base and the indicator.
of course, if indicator is properly chosen, equivalence point is equal to end-point. just keep in mind that their meanings are different.

http://www.chemguide.co.uk/physical/acidbaseeqia/phcurves.html
http://www.chemguide.co.uk/physical/acidbaseeqia/indicators.html


2.
color change can only be observed when the chgange is sharp.
from red to orange, it's not so obvious; from red to yellow, it's clear.
for the orange solution to change from orange to yellow, only one-or-two more drops are needed. this doesn't requires much more solution, but the change in pH could lead to sharp color change.


3.
range where color change is sharp.
usually, color change is sharp when one form of indicator is 10-times more concentrated than another.

say, pKa of phenolphthalein is 9.3
[In-][H+]/[HIn] = 10^(-9.3)
when one form is 10-times more concentrated, say, the basic form, then
[In-]/[HIn] = 10
and [H+] = 10^(-10.3)
pH = 10.3
similarly, when acidic form is more dominant, pH = 8.3
then, the working range of phenolphthalein is 8.3 ~ 10.3.

as a rule of thumb, pH of working range is its pKa value +/- 1 .

1. When the slope of a point becomes infinity, it attains the end point.