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[OLD] Ion activities


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From: Hillary A. Thompson

Subject: ion activities

When one produces an activity diagram, e.g. log (Al+++) vs pH, is it correct that the values on the y-axis are in fact activities of the dominant aqueous species and not the bare, unhydrolyzed ion, as is suggested by the axis label? And is the same true for compositional information provided for non-axis species, i.e., one provides the total activity (or concentration?) of all aqueous Mg (e.g.) species if one wishes to include Mg in the calculation? If one is trying to mimic a laboratory experiment in which one knows total ion concentrations, then, one inputs total concentrations (or activities?) for each element, rather than first conducting a calculation (does any part of GWB accomplish this?) to speciate the total ion concentration (and therefore must fix pH in that calculation) and then determining activity of the bare ion from its concentration. Is this correct?

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