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The Chemical Educator

ISSN: 1430-4171 (electronic version)

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Abstract Volume 16 (2011) pp 41-45

Mercury(II) Speciation in Natural Waters

Ermanno Vasca*, Francesco Farina, and Carla Manfredi

Department of Chemistry, University of Salerno, Fisciano (SA), Italy, evasca@unisa.it, and Department of Chemistry, University of Naples “Federico II”, Naples, Italy
Received March 4, 2010. Accepted April 9, 2010.

Published: 18 February 2011

Abstract. Mercury(II) speciation in natural waters is proposed as a tutorial example for students interested in equilibrium analysis. Accurate literature survey and database analysis are recommended as the starting point in the study. Through a step-by-step approach students are invited to build up a speciation model in which the contribution of Hg2+–chloride complexes, the hydrolysis of Hg2+, and the ternary HgOHCl(aq) species are taken into account in that sequence. Observations from simple potentiometric and ESI-MS experiments are suggested for the model refinement. It is shown how to use graphical methods and simple algebra to obtain a pictorial view of the equilibria and a quantitative interpretation of it, which nicely fits data processing software results. Changes in Mercury(II) speciation in passing from freshwaters to seawater are highlighted.

Key Words: In the Classroom; general chemistry; equilibrium analysis

(*) Corresponding author. (E-mail: evasca@unisa.it)

Article in PDF format (120 KB) HTML format

Supporting Materials:

The following information is available as Supporting Materials: (i) Evaluation of the concentration of the species at equilibrium in 5 mM HgCl2 using a relative logarithmic diagram; (ii) Determination of the pH of distilled water in equilibrium with atmospheric CO2; (iii) Drawing the predominance area diagram of the Hg2+-H2O-Cl- system; (iv) Drawing the logarithmic concentration diagram; (v) 3D pH-pCl plots; (vi) ESI-MS spectra of 5 mM HgCl2; (vii) The Specific Interaction Theory; (viii) HySS output in the Hg2+–H2O–Cl- system for different analytical composition of the solution; (ix) Handout for students (292 KB).



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