Question

Why do some substances require larger additions before a color change was seen? What does this indicate about the strength of the acid or base?

Answer 1

It depends on the substance you are adding. Some substances work only for strong bases or weak bases or strongs acids.

Example, if you have a weak base solution (pH=8) and you add phenolphthalein, then you need a lot of phenolpthalein drops to see a pink color change because phenolphthalein is for stronger bases.

Phenolphthalein addded to acids and weak bases have a colorless coloration. But if you add phenolphthalein to a strong base then the color changes to pink.