Determination of selective coefficients of monovalent anions by the conductive method

Studies on the separation of anions with anion exchange resin. I

Abstract

The progress of ion exchange reaction of a OH-type resin (Dowex 2) gives a continuous increase in the concentration of OH ion and a proportional increase in conductivity of the solution, and constant OH ion concentration and conductivity are reached on the equilibrium point of exchange reaction. Accordingly, an estimation of the rate of increase in conductivity should give an exchange velocity. According to the experiment of the authors, the ion exchange reaction took place as soon as the resin was immersed and an equilibrium was reached within 5 minutes. The concentration of OH ion could be sought by a simple calculation from the value of conductivity at the equilibrium stages; further-more, calculation of selective coefficient (anion exchange equilibrium constant), K^Anion_OH (25°C), was made. The results were :
BO₂^-<F^-<AsO₂^-<IO₃^-<BrO₃^-<Cl^-<(OH)^-<CN^-<NO₂^-<NO₃^-<ClO₃^-<Br^-<I^-<NCS^-.
The procedure of this method is more simple than the conventional titrimetric methods, the range of application is wide and there is a merit of being able to confirm the point just reaching the equilibrium.