Question

Why is bromophenol blue rather than phenolphthalein used as an indicator for the antacid titration?

Answer 1

An antacid is a substance which neutralizes stomach acidity, which in turn relieves heartburn, indigestion or stomach upset.

If you are titrating a strong acid and a weak base, the resulting solution is acidic, so you need an indicator that has a pH range that includes pH values below 7.0, like methyl orange, methyl yellow and bromophenol blue.

If you are titrating a weak acid and a strong base, the resulting solution is basic, so you need indicators with pH ranges with values above 7.0 like phenolphthalein, alizarine yellow R and thymolphthalein.

Since antacid is a substance which neutralizes stomach acidity hence resulting solution is acidic therefore we use bromophenol blue rather than phenolphthalein used as an indicator for the antacid titration.