The partitioning behavior of molecular iodine in liquid-liquid systems composed of water and an organic solvent has been used in the general chemistry laboratory curriculum to explore the concepts of thermodynamics.  Working in small groups, students use UV-vis spectroscopy to observe and quantify the iodine partitioning in several systems (in the form [I2]org/[I2]aq), each of which begins with a different concentration of dissolved iodine.   Further, each group conducts their work at a unique temperature.  Compiling and analyzing the class' temperature-dependent data allows students to calculate the enthalpy and entropy changes that accompany the movement of molecular iodine across the liquid-liquid interface.  Optional features of the experiment include comparison to thermodynamic values calculated from molecular modeling programs and utilization of different liquid-liquid interfaces to observe the effect of the organic solvent on the resulting behavior.

Thermodynamic study of solute partitioning:  A second-semester chemistry experiment

245th National Meeting (2013)

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