ISSN:
1572-8927
Keywords:
Benzoic acid
;
dissociation constant
;
ionization constant
;
potentiometry
;
ionic strength
;
temperature and pressure dependence
;
thermodynamics
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
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 HCl solution at seven temperatures from 5 to 250°C and at seven ionic strengths ranging from 0.1 to 5.0 molal (NaCl). 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: logKa=−4.206±0.006, ΔH a o =0.3±0.3 kJ-mol−1, ΔS a o =−79.6±1.0 J-mol−1-K−1, and ΔC p;a o =−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.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01150876
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