Question

In an acid/base titration, why must the indicator (phenolphthalein) be a strong dye?

Answer 1

I don't know what you mean by a "strong" dye? I assume you mean it has an intense color. If that is your definition of a strong dye, we want a visual indicator to be so intensely colored that the tiniest amount of titrant over the equivalence point will be enough to color the solution visible to the eye.

Answer 2

Thanks