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. (C) 2000 American Institute of Physics. [S0034-6748(00)01801-3].