Cation structure maker effect

All the non-freezing water values in Figure 7 were determined in 1 M salt solutions. It was therefore of Interest to explore the effect of salt concentration. Figure 8 shows the effect of salt concentration for one structure breaker (KNO ) and one structure maker (Ll-SO ). The results show that Ll2S0 is strongly concentration dependent while KNO is concentration independent. These results cast some doubt that the results in Figure 7 are due solely to the cation of the salt solution. Further work is needed for clarifying these results. 

The solutes which make up aqueous solutions can either promote or disrupt the three-dimensional structure of water. Hydrogen ions (H" ") and hydroxide ions (OH") are the ultimate structure makers in aqueous solutions, as they fit perfectly into the water structure. Various water miscible solvents (e.g., methanol, ethanol, acetone) have more-or-less predictable effect on the structure of water. Small, hard-sphere metal cations tend to promote order in the solution while large cations tend to disrupt the structure. Among typical anions, fluoride is a strong structure maker, sulfate and nitrate less efficient structure makers, while the heavy halides and thiocyanate disrupt the water structure. Most effective among anions encountered in separations in... 

The effects of the ions on the structure of the water were then described by Marcus [51, 53] as the ratios AG bj, = A i" °according to Equation 5.13. The water stracture effects of ions according to this approach are shown in Table 5.2 — structure makers having positive values and structure-breakers negative values. These results are unsatisfactory, due to the inaccuracy of the AjU,°° ° data, making the divalent cations Ba and Cd appear as strong water-structure breakers and LP as a mild structure breaker, contrary to aU other information concerning these ions. The available data for the nine alkah metal and hahde ions appear to be the most accurate, and their correlations with other quantities that describe the water structural effects of ions are ... 

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