Mercury(II) Speciation in Natural Waters

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.