The dissociation constants of ethylene diammonium and hexamethylene diammonium ions from 0° to 60° C

Abstract

The two acid dissociation constants of the ethylene diammonium ion and the hexamethylene diammonium ion in water have been determined, using an e.m.f. method, from 0 to 60° C. Measurements have been made at several ionic strengths to allow thermodynamic dissociation constants to be derived, and from these the free energy, heat content, entropy and heat capacity changes accompanying the dissociations have been computed. These quantities are discussed in relation to the size of the diamine molecule, and orientation of solvent molecules by the ionic charges. It is concluded that the range over which a single ionic charge causes a significant change in the structure of liquid water is about 5 Å.