Let us examine a simple acid base reaction....
NaOH(aq) + HCl(aq) rarr NaCl(aq) +H_2O(l)
And for the purposes of the example we assume we add a solution of sodium hydroxide FROM a burette, to a KNOWN volume of HCl(aq) of KNOWN concentration.
And let us consider the pH of such a typical strong acid/strong base titration...
useruploads.socratic.org)
(Perhaps I could have used a BIGGER illustration...)
Now the equivalence point is CLEARLY at pH=7.0...and while ideally, we would like the indicator to change colour at this point, as shown in the graph, the pH changes sigmoidally over SIX whole pH units. And if you look at the abscissa of the "x-axis", the dramatic pH change occurs over the addition of 0.01*mL...and this is about 1*"drop" of titrant...and so several indicators are feasible in the given scenario. As always with these titrations, we titrate to the POINT of colour change, NOT the colour change itself.
