Dissociation quotients of succinic acid in aqueous sodium chloride media to 225°C

Abstract

The first and second molal dissociation quotients of succinic acid were measured potentiometrically with a hydrogen-electrode, concentration cell. These measurements were carried out from 0 to 225°C over 25° intervals at five ionic strengths ranging from 0.1 to 5.0 molal (NaCl). The dissociation quotients from this and two other studies were combined and treated with empirical equations to yield the following thermodynamic quantities for the first acid dissociation equilibrium at 25°C: log K_1a=−4.210±0.003; ΔH ⁰_1a =2.9±0.2 kJ-mol⁻¹; ΔS ⁰_1a =−71±1 J-mol⁻¹-K⁻¹; and ΔC ⁰_p1a =−98±3 J-mol⁻¹-K⁻¹; and for the second acid dissociation equilibrium at 25°C: log K_2a=−5.638±0.001; ΔH ⁰_2a = −0.5±0.1 kJ-mol⁻¹; ΔS ⁰_2a =−109.7±0.4 J-mol⁻¹-K⁻¹; and ΔC ⁰_p2a = −215±8 J-mol⁻¹-K⁻¹.