If we have an indigestion we take a antacid.. The acid produced in our stomach is neutralized by the antacid(Magnesium hydroxide).
Whenever we use bathroom acid or any acid to clean a marbled floor. The marbled floor(Calcium carbohydrate) reacts with the acid/bathroom acid.
Whenever our hand are wettened due to rain we use soaps... The soaps neutralize the acidic content in the rain