Photo by C Lloyd at SSERC (Public Domain)
Benzoic acid can be prepared by the alkaline hydrolysis of the ester, ethyl benzoate.
If sodium hydroxide is used, then the residual solution will contain sodium benzoate. Insoluble benzoic acid can be displaced from this solution by acidification. It can then be filtered off and purified by recrystallisation from water. The percentage yield of benzoic acid can be calculated and its melting point determined.
Hydrolysis of ethyl benzoate – pupil guide
Hydrolysis of ethyl benzoate – Teacher’s guide
Hydrolysis of ethyl benzoate – Risk assessment