Chem q ab titration

For the titration with weak acid, we cannot use weak alkali, because there is only a gradual change in PH during the course of titration. The endpoint resulted will not be accurately determined with any indicator.

As methyl orange pKa is 3.7 and its active range is 3.1 - 4.4 , so methyl orange can only be used in titration of strong acid and weak alkali. But titration of vinegar and sodium hydroxide is titration of weak acid and strong alkali, so only indicator with active range 7.5 - 10.5 e.g. phenolphthalein (8.3 - 10) should be used.

I hope this can help your understanding. =)