ENTHALPIES OF DILUTION OF ALKALINE AND ALKALINE-EARTH P-TOLUENESULFONATES

Enthalpies of dilution (Delta H-D, c --> 0.002 mol-dm(-3)) of aqueous solutions of lithium, sodium, potassium, cesium, calcium, magnesium, a nd strontium salts of p-toluenesulfonic acid were measured at several temperatures between, 0 degrees and 40 degrees C, and over a broad con centration range. For monovalent ions the following results were obtai ned: (i) the enthalpy of dilution for lithium p-toluenesulfonate becam e more exothermic on increasing the concentration, while those of sodi um, potassium, and cesium salts exhibited a maximum, (ii) enthalpies o f dilution were strongly dependent on the ionic radius of the cation, and the -Delta H-D values increase in the order Li > Na > K > Cs. This parallels the behavior of the same quantity in alkaline poly(styrenes ulfonate) 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 po ly(styrenesulfonate) solutions, the enthalpies of dilution were exothe rmic for all temperatures and salts.