Original scientific paper

Determination of Stability Constants of Chlorocadmium Complexes in Water from Electromotive Force Measurements

Renato Tomaš ; Department of Physical Chemistry, Faculty of Chemical Technology, University of Split, N. Tesle 10, HR-21000 Split, Croatia
Marija Višić ; Department of Chemistry, Faculty of Natural Sciences, Mathematics and Education, University of Split, N. Tesle 12, HR-21000 Split, Croatia
Ivo Tominić ; Department of Physical Chemistry, Faculty of Chemical Technology, University of Split, N. Tesle 10, HR-21000 Split, Croatia
Vesna Sokol ; Department of Physical Chemistry, Faculty of Chemical Technology, University of Split, N. Tesle 10, HR-21000 Split, Croatia

Abstract

A potentiometric method involving a three-electrode cell was applied to determine the concentration stability constants (K'_n) of chlorocadmium complexes in water at 298.15 K and ionic strength I=1 mol dm-3. Initially, calibration diagrams were derived for the cadmium and chloride ion, based on the measurements of the potential difference between the glass and the cadmium-amalgam electrode for known Cd2+ ion concentrations, and between the glass and AgCl / Ag electrode for known Cl- ion concentrations. To determine the concentrations of free Cd2+ and Cl- ions by means of calibration diagrams, potential differences between the same electrodes were measured in the three-electrode cell by changing the concentration of total chlorides while keeping the concentration of cadmium ions constant. These data were used to determine the concentration stability constants of the formed complexes CdCl+, CdCl₂, and CdCl₃- by applying Leden’s graphical method and three numerical methods: nonlinear regression without scaling, nonlinear regression with scaling, and orthogonal polynomials. The two latter methods gave identical constants: 24.6 (CdCl+), 68 (CdCl₂), and 69 (CdCl₃-). The obtained concentration stability constants were compared with the available data for the same complexes obtained from the electromotive force measurements (e.m.f.) of the concentration cell with transference, calculated using the same methods. As a result, it was possible to compare both experimental methods applied in determining the concentration stability constants of chlorocadmium complexes in water medium at 298.15 K and ionic strength I=1 mol dm-3.

Keywords

direct potentiometry; three-electrode cell; chlorocadmium complexes; concentration stability constants

Hrčak ID:

131774

URI

https://hrcak.srce.hr/131774

Publication date:

1.2.2001.

Visits: 1.324 *