The pair distributions and the osmotic coefficient in anomalous electrolytes up to concentrations c≈ 1 mol/1

The osmotic coefficient of anomalous electrolytes up to concentrations c ≈ 1 mol/l is explained by the pair distributions n(r) = exp[-β(Vc(r) + V(hs)(r) + V1(r))]. Here Vc(r) is a screened Coulomb potential, V(hs)(r) a hard sphere potential and V1(r) = −A/r6 a short range attractive potential. For the contact distances R++, R−− and R+− of the hard sphere potentials between ions with the same sign of their charges (++,−−) and ions of opposite charges (+−) the relations R++ = R−− = R and R+− = q1R with 0 < q1 < 1 are assumed. In contrast to a previous paper the parameter q1 takes a fixed value q1 ≈ 0,8. The constant A is determined by the fraction q2 defined by A/R6 = q2(Z2e2/DR) where the positive integer Z is the charge number of the ions and D the dielectric constant of the solvent. The numerical calculation of the osmotic coefficient of 1-1-valent hydrous electrolytes in the range of temperature 273 K ⩽ T ⪅ 293 K shows that the anomalous electrolytes are described by fractions q2 in the range 0,25 ⪅ q2 ⪅ 0,5 if the contact distances R are in the range 3 Å ⩽ R ⩽ 7 Å.