DISSOCIATION QUOTIENTS OF D-GALACTURONIC ACID IN AQUEOUS-SOLUTION AT 0.1 MPA TO 1 MOLAL IONIC-STRENGTH AND 100-DEGREES-C

The molal dissociation quotients of D-galacturonic acid were measured potentiometrically in a newly-designed, hydrogen-electrode concentrati on cell from 5 to 100-degree-C at four ionic strengths ranging from 0. 1 to 1.0 mol-kg-1 using sodium trifluoromethanesulfonate (NaF3CSO3) as the supporting electrolyte. These quotients were fitted in the all an ionic (isocoulombic) form by an empirical equation incorporating three adjustable parameters. When combined with the known dissociation quot ient for water in the same medium, this treatment yielded the followin g thermodynamic quantities for the acid dissociation equilibrium at 25 -degrees-C and infinite dilution: log K(H) = -3.490+/-0.011, DELTAH(H) degrees = 0.4+/-0.2 kJ-mol-1, DELTAS(H)degrees = -65+/-1 J-mol-1-K-1, and DELTAC(p,H)degrees = -231+/-8 J-mol-1-K-1. Comparisons are made wi th the corresponding results of a limited number of previous studies c arried out near ambient conditions.