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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,, 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:

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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