Kw = (0.25O2(aq) + H+ + e-)/(0.5H2O) where Kw = -11.385 -11.385 = .25log(O2) + log(H+) + log(e-) - 0.5log(H2O) or assuming log(H2O) ~ 0 -11.35 = .25log(O2) - pH - pe > 1) Is "O2" equal to the molar concentration of O2 calculated from the Dissolved Oxygen in mg/L? (O2) represents activity of O2, which is close enough to molality not to worry about it. > 2) Is "H+ " equal to pH or the activity of hydrogen ion, or something else? (H+) is the activity of hydrogen ion, log(H+) = -pH 3) Is "H2O" equal to the activity of water (in which case it can be assumed to be 1.0)? Yes. 4) Is "e-" equal to pe? (e-) is the conventional activity of the electron, log(e-) = -pe. But, my own feeling is that the Sato relation is just a kluge. It has the effect of lowering the calculated pe several units from what you would calculate from DO. The main reason it was done was to try to reconcile platinum electrode measurements, which are not very useful except maybe in the presence of iron and sulfide. David David Parkhurst (dlpark@xxxxxxxx) U.S. Geological Survey Box 25046, MS 413 Denver Federal Center Denver, CO 80225 Project web page: https://wwwbrr.cr.usgs.gov/projects/GWC_coupled
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