ISSN:
1572-8927
Keywords:
Malonic acid
;
propanedioic acid
;
dissociation constants
;
cadmium
;
complexation constants
;
sodium trifluoromethanesulfonate
;
potentiometry
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract The molal formation quotients for cadmium–malonate complexes were measured potentiometrically from 5 to 75°C, at ionic strengths of 0.1, 0.3, 0.6 and 1.0 molal in aqueous sodium trifluoromethanesulfonate (NaTr) media. In addition, the stepwise dissociation quotients for malonic acid were measured in the same medium from 5 to 100°C, at ionic strengths of 0.1, 0.3, 0.6, and 1.0 molal by the same method. The dissociation quotients for malonic acid were modeled as a function of temperature and ionic strength with empirical equations formulated such that the equilibrium constants at infinite dilution were consistent, within the error estimates, with the malonic acid dissociation constants obtained in NaCl media. The equilibrium constants calculated for the dissociation of malonic acid at 25°C and infinite dilution are log K 1a=-2.86 ± 0.01 and log K 2a=-5.71 ± 0.01. A single Cd–malonate species, CdCH2C2O4, was identified from the complexation study and the formation quotients for this species were also modeled as a function of temperature and ionic strength. Thermodynamic parameters obtained by differentiating the equation with respect to temperature for the formation of CdCH2C2O4 at 25°C and infinite dilution are: K = 3.45 ± 0.09, ΔS° = 7 ± 6 kJ-mol-1, ΔS° = 91 ± 22 J-K--mol-1, and ΔC p o =400±300 JK-1mol-1.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1022638817245
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