Potentiometric study of the dissociation quotients of aqueous dimethylammonium ion as a function of temperature and ionic strength

The acid dissociation equilibria involving aqueous dimethylammonium ion in the reaction (CH3)(2)NH2+ reversible arrow (CH3)(2)NH + H+ were measured po tentiometrically with a hydrogen-electrode concentration cell from (0 to 29 0) degreesC in sodium-trifluoromethanesulfonate (NaTr) solutions at ionic s trengths of (0.1, 0.3, and 1) molal. The molal dissociation quotients and s elected literature data at infinite dilution were fitted by an empirical eq uation involving six adjustable parameters involving functions of temperatu re, solvent density, and ionic strength. This treatment yielded the followi ng thermodynamic quantities at 25 degreesC and infinite dilution: log K-d = -10.77 +/- 0.02, DeltaH(d) = (50.8 +/- 0.7) kJ(.)mol(-1), DeltaS(d) = (-35 .8 +/- 2.5) J(.)K(-1.)mol(-1), DeltaC(p,d) = (116 +/- 11) J(.)K(-1.)mol(-1) , and DeltaV(d) = (-4.3 +/- 2.5) cm(3.)mol(-1).