A Colorful Laboratory Investigation of Hydrophobic Interactions, the Partition Coefficient, Gibbs Energy of Transfer, and the Effect of Hofmeister Salts

Abstract

Only a few pedagogical experiments have been published dealing specifically with the hydrophobic interaction though it plays a central role in biochemistry. A set of experiments is presented in which students partition a variety of colorful indicator dyes in biphasic water/organic solvent mixtures. Students monitor the partitioning visually and quantify it using inexpensive Spectronic 20 spectrophotometers. Through the experiments, the students explore the effects of charge, alkyl chain length, the presence of Hofmeister salts, and temperature on a variety of parameters related to hydrophobicity such as the partition coefficient, and the thermodynamic parameters of transfer of a molecule from the aqueous layer into the organic layer.