The partitioning of para-nitrophenol (PNP) across the interface between two immiscible liquids was studied by following the concentration of the solute as it migrated between adjacent solvent layers of liquid-liquid systems composed of water and an organic solvent. Ultraviolet-visible spectroscopy was used to determine the concentration of PNP in each solvent layer. Rate constants for the migration of PNP across the interfaces were observed as functions of initial solute location and organic solvent polarity. The largest rates were observed when the hydrophilic solute moved from the organic to the aqueous phase in systems containing the most non-polar organic solvents. The results of this work and the procedures employed have been used to develop a prototype of a small-scale kinetics experiment suitable for a general chemistry course.