Dissociation Quotient of Benzoic Acid in Aqueous Sodium Chloride Media to 250°C

Authors

Richard Kettler, University of Nebraska-LincolnFollow
David J. Wesolowski, Oak Ridge National Laboratory
Donald A. Palmer, University of Nebraska-Lincoln

Date of this Version

1995

Comments

Published in Journal of Solution Chemistry, Vol. 24, No.4, 1995

Abstract

The dissociation quotient of benzoic acid was determined potentiometrically in a concentration cell fitted with hydrogen electrodes. The hydrogen ion molality of benzoic acid/benzoate solutions was measured relative to a standard aqueous IiCI solution at seven temperatures from 5 to 250°C and at seven ionic strengths ranging from 0.1 to 5.0 molal (NaCI). The molal dissociation quotients and selected literature data were fitted in the isocoulombic (all anionic) form by a six-term equation. This treatment yielded the following thermodynamic quantities for the acid dissociation equilibrium at 25°C and 1 bar: log K_a = -4.206±0.006, ΔH_å=0.3±0.3 kJ-mol^-1, ΔS_å=-79.6±1.0 J-mol^-1-K^-1, and ,ΔC_{p̊, a} = -207±5 J-mol^-1-K^-1. A five-term equation derived to describe the dependence of the dissociation constant on solvent density is accurate to 250°C and 200 MPa.