Thermodynamics of ion pairs in mixed solvents. I. The standard associationconstant of the ion pair [MgSO4]o in {0.03226 CO(NH2)(2)+0.96774 H2O}

The standard potential of the (Ag, AgCl) electrode E-o, the standard second ionization constant of sulfuric acid K-2, and the standard association con stant of the ion pair [MgSO4](o), K in (0.03226 CO(NH2)(2) + 0.96774 H2O) a t five temperatures from 278.15 K to 318.15 K were determined from precise e.m.f. measurements of different cells without liquid junction. The depende nce of pK on temperature T is expressed by the empirical equation pK = 6.61 7 - 777.9 . (K/T) - 0.02001 . (T/K). The other thermodynamic functions of t he association process were also calculated and show that the driving force for the process is the entropy of association. (C) 2001 Academic Press.