Enthalpies of dilution of alkaline and alkaline earthp-toluenesulfonates

Enthalpies of dilution (H_D, c0.002 mol-dm^–3) of aqueous solutions of lithium, sodium, potassium, cesium, calcium, magnesium, and strontium salts of p-toluenesulfonic acid were measured at several temperatures between 0° and 40°C, and over a broad concentration range. For monovalent ions the following results were obtained: (i) the enthalpy of dilution for lithium p-toluenesulfonate became more exothermic on increasing the concentration, while those of sodium, potassium, and cesium salts exhibited a maximum, (ii) enthalpies of dilution were strongly dependent on the ionic radius of the cation, and the-H_D values increase in the order, Li>Na>K>Cs. This parallels the behavior of the same quantity in alkaline poly(styrenesulfonate) solutions. For divalent ions the situation was different; Mg, Ca, and Sr p-toluenesulfonates showed little temperature dependence and almost no dependence on the nature of the ion. In contrast with poly(styrenesulfonate) solutions, the enthalpies of dilution were exothermic for all temperatures and salts.