Dissociation Quotients of Malonic Acid in Aqueous Sodium Chloride Media to 100°C1

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

1992

Comments

Published in Journal of Solution Chemistry. Vol. 21. No.8. 1992

Abstract

The first and second molal dissociation quotients of malonic acid were measured potentiometrically in a concentration cell fitted with hydrogen electrodes. The hydrogen ion molality of malonic acidJbimalonate solutions was measured relative to a standard aqueous HCI solution from 0 to 100°C over 25° intervals at five ionic strengths ranging from 0.1 to 5.0 molal (NaCl). The molal dissociation quotients and available literature data were treated in the all anionic form by a seven-term equation. This treatment yielded the following thermodynamic quantities for the first acid dissociation equilibrium at 25°C: log K_1a = -2.852 ± 0.003. ΔH_1̊a = 0.1 ±0.3 kJ-mol^-1. ΔS_1̊a = -54.4±1.0 J-mol^-1-K^-1 and ΔC_p̊,1a = -185±20 J-mol^-1-K^-1. Measurements of the bimalonatelmalonate system were made over the same intervals of temperature and ionic strength. A similar regression of the present and previously published equilibrium quotients using a seven- term equation yielded the following values for the second acid dissociation equilibrium at 25°C: log K_2a = -5.697 ± 0.001. ΔH_2̊a = -5.13±0.11 kJ-mol^-1, ΔS_2̊a = -126.3±0.4 J-mol^-1-K^-1. and ΔC_p̊,2a = -250+10 J-mol^-1-K^-1.