Croatica Chemica Acta, Vol. 77 No. 3, 2004.
Original scientific paper
Investigation of the Complex Forming Reactions of Cd2+ and Cl– Ions in 2-Butanone + Water Mixtures by Direct Potentiometry
Renato Tomaš
orcid.org/0000-0002-6154-3709
; Department of Physical Chemistry, Faculty of Chemical Technology, University of Split, Teslina 10, 21000 Split, Croatia
Ivo Tominić
; Department of Physical Chemistry, Faculty of Chemical Technology, University of Split, Teslina 10, 21000 Split, Croatia
Vesna Sokol
; Department of Physical Chemistry, Faculty of Chemical Technology, University of Split, Teslina 10, 21000 Split, Croatia
Marija Višić
; Department of Chemistry, Faculty of Natural Sciences, Mathematics and Education, University of Split, Teslina 12, 21000 Split, Croatia
Abstract
The complex forming reactions of cadmium and chloride ions in 2-butanone + water mixtures (with mass fraction of the organic component 0.05, 0.10 and 0.15) at three ionic strengths and three temperatures were investigated by the method of direct potentiometry by means of calibration straight lines. As that experimental technique has not yet been tested in mixed solvents, first, measurements in 10 % (mass fraction) t-butanol at ionic strength of 1 mol dm–3 and temperatures 288.15, 298.15 and 313.15 K were performed and stability constants of chlorocadmium complexes were redetermined. Comparing these values with those obtained by measuring the e.m.f. of the concentration cell with transference, reproducibility and applicability of direct potentiometry in that mixed solvent were proven. According to statistical parameters, direct potentiometry retains the precision of the potentiometry of the concentration cell with transference, but, due to the absence of junction potential, it is undoubtedly more accurate. In the mixtures of water and 2-butanone, CdCl+, CdCl2 and CdCl3 – complexes were found as well as their concentration stability constants (K'n) by the method of orthogonal polynomials for each ionic strength and temperature. By the extrapolation of semiempirical straight lines to zero ionic strength, thermodynamic stability constants (Kon) were obtained. It was found that the Kon values increase with the increase of temperature and with the decrease of relative permittivity of the solvent. From the temperature dependence of Kon, thermodynamic quantities for the complex forming reactions were calculated; all the reactions are spontaneous, endothermic and lead to an increase in entropy.
Keywords
2-butanone + water mixtures; chlorocadmium complexes; direct potentiometry; stability constants; thermodynamic quantities
Hrčak ID:
102953
URI
Publication date:
25.10.2004.
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