Acid-base and its neutralization behaviors were analyzed with recently reported dissociation constant data determined by electrical conductivity, UV-Vis and pH methods at 400 degreesC and densities ranging from 0.3 to 1.0 g/cm(3). The systems are HCl, HNO3, H2SO4, phenol, beta-naphthol, beta-naphthoic acid, NH4OH, alkali metal hydroxides and alkali metal chlorides. Among these systems, HCl and KOH are strongest acid and base, respectively. Then neutralization behaviors of HCl + NaOH, dissociation behavior of NaCl and titration behavior of HCl + LiCl and LiOH + LiCl were studied with dissociation constant data and activity coefficient formulation. The results gave informations that (1) the equivalence point for neutralization was placed at a little smaller NaOH concentration than initial HCl concentration, (2) NaCl solution behaved as a base, (3) H+ and OH-molalities in HCl and LiOH solutions, respectively, were decreased with increasing LiCl concentration. (C) 2003 Elsevier B.V. All rights reserved.