If you forget to add phenolphthalein solution to a vinegar solution(after adding NaOH solution), how might you salvage the titration?

Answer 1

There are several ways but the main concept is to add enough acid to the titration flask to bring the pH back to the acid side. How to do that?
1. Add a primary standard acid such as potassium hydrogen phthalate then retitrate with the NaOH.
2. Add a measured amount (from a buret or a pipet) of a known molarity of HCl, then retitrate to the equivalence point with the NaOH.