Transference numbers of aqueous picric acid at 25°C and a re-examination of the transference numbers of aqueous tartaric acid

Abstract

The anion-constituent transference numbers of 0.005, 0.01 and 0.02 M aqueous solutions of picric acid have been measured at 25°C using the direct moving boundary method. Care was taken to avoid photochemical effects during the runs, and the results were extrapolated to zero current. Their analysis, and particularly also the analysis of certain properties of solutions of alkali metal picrates, provide evidence for the existence of dimeric picrate anions (K_form= 2–3 1. mol^–1) and possibly other species. The transference numbers of another acid, D-tartaric, were redetermined at 0.02, 0.05, and 0.1 M using a closed silver succinate cathode. Their concentration dependence is consistent with the presence of hydrogen-bonded triple ions with a stability constant of 0.61. mol^–1.