ISSN:
1572-8927
Schlagwort(e):
Malonic acid
;
propanedioic acid
;
dissociation constants
;
thermodynamics
;
potentiometry
;
ionic strength
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Chemie und Pharmazie
Notizen:
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 acid/bimalonate solutions was measured relative to a standard aqueous HCl 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: logK 1a =-2.852±0.003, ΔH 1a /o =0.1±0.3 kJ-mol−1, ΔS 1a o =−54.4±1.0 J-mol−1-K−1, and ΔC p,1a o =−185±20 J-mol−1-K−1. Measurements of the bimalonate/malonate 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: logK2a=−5.697±0.001, ΔH 2a o =−5.13±0.11 kJ-mol−1, ΔS 2a o =−126.3±0.4 J-mol−1-K−1, and ΔC p,2a o =−250+10 J-mol−1-K−1.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/BF00651513
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