Acidic dissociation constant and related thermodynamic quantities for diethanolammonium ion in water from 0 to 50 °C

Abstract

The dissociation constants of diethanolamine (2:2'-dihydroxydiethylamine) and its conjugate acid were determined by electromotive force measurements of the cell [formula] in the temperature range 0 to 50 °C. The acidic dissociation constant (Kbh) of the diethanolammonium ion is given by [equation] where T, the temperature on the Kelvin scale, lies between 273.15 and 323.15°. From this equation were calculated DeltaG°, the change in free energy; DeltaH°, the change in heat content; DeltaS°, the change in entropy; and DeltaC°p , the change in heat capacity that accompany the dissociation of 1 mole of diethanolammonium ion in the standard state. At 25 °C, -log Kbh=8.883 ; DeltaG°= 50,682 joule mole-1; DeltaH°= 42,400 joule mole-1; DeltaS°=-27.8 joule deg-1mole-1; and DeltaC°p=49 joule deg-1mole-1 .