THE ELECTRICAL CONDUCTANCE OF STRONG ELECTROLYTES: A TEST OF STOKES EQUATION

Abstract

The equation recently put forward by Wishaw and Stokes, purporting to reproduce the equivalent conductance of concentrated solutions of strong electrolytes, has been tested by applying it to the experimental data of Campbell, Kartzmark et alii. The agreement between the calculated and observed values of Λ is astonishingly good, in the case of lithium nitrate up to a concentration of 7 molar. The deviations found for silver nitrate and ammonium nitrate are attributed to ion-pair formation and a dissociation "constant" deduced (for silver nitrate) which does show approximate constancy; a similar calculation by Stokes for ammonium nitrate shows even better constancy. Since the Stokes' equation is fully theoretical and contains only quantities to which physical meaning can be attached, it is to be preferred to any empirical, or semiempirical, equation. The Stokes' equation, being merely an extension of the Debye–Hückel– Onsager concept, cannot be expected to apply to concentrations greater than, say, 5 N. Attention is again drawn to the empirical observation that in the region of very high concentration the plot of Λ versus log C is a true straight line.