Dissociation constant of 4-aminopyridinium ion in water from 0 to 50 C and related thermodynamic quantities

The d issociat ion co nstant of 'l -a minopy ridinium ion in water a t 11 tempcratures from 0° to 50° C has bee n d eterm ined from elec tromotive forc e meas urem en ts of 19 approximat e ly eq ulmolal aqu eou s buffer solutions of 4-aminopyridin c a nd 4-a minopyridillium chlorid e.Cells wi thout liq uid jun ction were used ; the cell is represe nted as foll ows:where In is molali ty .Between 0° and 50° C, t he di ssociation constant (K bh) is given as a function of temperature ( T ) in d egr ees K elvi n by 2575.8 -log K bh = -y;-+ 0.08277 + 0.0013093 T The changes of Gibb fr ee e nergy (Ll.(,!0) , o f ent halp y (tlHO) , of en tropy (Ll.SO) , and of heat capacity (tlCp O) for the d issociation process i n t he standard state we re calculated from the constan ts of t hi s equation.At 25° C t he following values were found :-log K bh = 9.114, tlG o= 52, 013 j m ole -I , tlHo= 47, 090 j m ole-I, tlSo= -16.5 j deg-I mole -I, tl C; = -15 j deg-I mole -I.Thermody namic co nstants for the basic di ssocia t ion of 4-amin opyridin e a t 25° C were also compu ted.