A Simple At-Home Titration: Quantifying Citric Acid in Lemon Juice with Baking Soda and Mentos

Abstract

At-home chemistry experiments are increasingly important to enable high-quality online and hybrid instruction. These class modalities provide significant challenges and also dramatically expand the accessibility of education to those who work or care for family during traditional school hours or have significant commutes to campus. This work demonstrates a novel approach to quantifying citric acid in lemon juice using baking soda as a titrant that requires no specialized equipment. Despite being a weak acid/weak base titration, the gas evolution of carbon dioxide brings this reaction to near completion. Since this process can be relatively slow, the candy Mentos is used to drive rapid gas evolution. The cessation of this vigorous gas evolution is used to track the end point of the titration. The results of this at-home titration were compared to a traditional in-person titration of citric acid in lemon juice (using sodium hydroxide as the titrant and a phenolphthalein indicator) performed by the same students. The at-home titration and the in-person titration yielded citric acid concentrations in lemon juice of 0.20 M (±0.08 M) and 0.25 M (±0.03 M), respectively.