Calculation of thermodynamic data from voltammetry of solid lead and mercury dithlocarbamate complexes mechanically attached to a graphite electrode

Alan M. Bond, Fritz Scholz

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Abstract

Solid lead and mercury dithiocarbamate complexes can be attached to the surface of a paraffin impregnated graphite electrode by simple mechanical transfer of small amounts of the solid material. The voltammetric reduction of these highly insoluble compounds, using the graphite electrode and an aqueous electrolyte, generates the metal and soluble dithiocarbamate ligand anions. The combination of diffusion of the ligand away from the electrode and the formation of the metal deposit on the electrode surface lead to the observation of the chemically reversible redox couple M(dtc)2 + 2e- ⇄ M↓ + 2dtc- (M = Pb, Hg; dtc- = substituted dithiocarbamate) during the second and subsequent scans of cyclic voltammograms. This process may be used to measure the formal potential for the reaction and enable the calculation of conditional stability constants (β2 values) to be made for the equilibria M2+ + 2dtc- ⇄ M(dtc)2. Thus, voltammetric measurements of solid dithiocarbamate complexes mechanically attached to a graphite electrode give ready access to thermodynamic data which are difficult or impossible to obtain by other techniques. The determination of β2 for 11 lead and 17 mercury dithiocarbamate complexes reveals a previously unrecognized linear correlation between log β2 and the molecular weights of the complexes.

Original languageEnglish
Pages (from-to)7460-7465
Number of pages6
JournalJournal of Physical Chemistry
Volume95
Issue number19
Publication statusPublished - 1 Dec 1991

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