Submitted to: Journal of Chemical Education
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/14/2005
Publication Date: 2/1/2006
Citation: Loyo-Rosales, J.E., Rosales-Rivera, G.C., Rice, C., Torrents, A. 2006. Linking laboratory experiences to "the real world": the extraction of octylphenoxyacetic acid from water. Journal of Chemical Education. 83(2):248-249. Interpretive Summary: A simple student experiment is presented that demonstrates conversions of an organic water-soluble salt, the sodium salt of octylphenoxyacetic acid, to an organic-solvent-soluble organic acid. At neutral pH the sodium salt of this molecule dissociates and dissolves in water, but when excess acid is added to the solutions, the hyronium ions associate where the sodium ion was attached and cause the molecule to become insoluble (precipitate). This precipitated form is then captured with an organic solvent which will not mix with the water. Isolation of this organic phase from the mixture allows capture of the originally water soluble salt of this molecule now in its acid form. The method provides students the opportunity to observe directly salt/acid transformations and allows them to to gain experience with standard analytical equipment such as a balance, separatory funnel, rotary evaporator and cylinders and pipettes.
Technical Abstract: A laboratory experiment is presented that links several chemical concepts to the extraction of a water pollutant (octylphenoxyacetic acid, OPC) with a method used in actual research. A known amount of the sodium salt of the OPC is dissolved in water, transformed to the acid (insoluble) form, and extracted using dichloromethane. These changes can be followed visually due to conspicuous changes in solution turbidity. The experiment allows students to learn and/or apply basic experimental techniques such as the use of ordinary laboratory glassware (e.g. cylinders and pipettes), analytical balance, a separatory funnel, and rotary evaporator; proper handling and disposal of strong acids and solvents; and the application of concepts such as acid-base reactions, stoichiometry and polarity. At the same time, it demonstrates a direct application of these concepts to a current research topic.