Studies on Sulphate Complexes. Part I. Potentiometric Investigation of Li+, Na+, K+, Rb+ and Cs+ Complexes at 37 °C and 0.03 < I < 0.5

The formation of complexes between sulphate ion and the alkali metal ions (M+ = Li+, Na+, K+, Rb+ or Cs+) was investigated. The experiments were carried out measuring potentiometrically the hydrogen ion concentration, at t = 37°C and variable ionic strengths (0.03 ≤ I ≤ 0.5 mol dm-3). For each alkali metal ion, in addition to the value of the stability constant, we obtained the parameters which define the dependence of the stability constant on ionic strength. The order of stability for [M(SO4)]- complexes is Li+ > Na+ < K+ < Rb+ < Cs+. The results seem to confirm that the differences in the protonation constants obtained using different ionic media may be explained in terms of complex formation between the ligand and the alkali metal ions.