Measurement of solute dipole moments in dilute solution: A simple three-terminal cell

The construction of a simple, thermostated, three-terminal cell for the measurement of the dipole moment of polar solutes in nonpolar solvents is described. Using a General Radio Company bridge, we demonstrate the accurate measurement of the dielectric constants of p-xylene and benzene, as well as the molecular dipole moments of acetonitrile in p-xylene and p-nitroaniline in benzene. Capacitance measurements of dilute solutions (10−2–10−3 M) using less than 10 ml of solution are possible with this apparatus. The Debye and Hedestrand equations are used to extract the dipole moments from the capacitance measurements.