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

Document Type

Article

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.