A Potentiometric Study of Ferric Ion Complexes in Synthetic Media and Seawater

An investigation of ferric ion complexing has been conducted in synthetic media and seawater at 25°C. Formation constants were potentiometrically determined for the species FeCl2+, FeCl2+, FeOH2+, and Fe(OH)2+ at an ionic strength of 0.68 m. Formation constants for the ferric chloride complexes were determined as Clβ1 = 2.76 and Clβ2 = 0.44. In a study of the reaction Fe3+ + nH2O ⇌ Fe(OH)n(3−n)+ + nH+ in NaClO4, NaNO3 and NaCl the formation constants ∗β1and∗β2 \u3e∗β1and∗β2 were shown to be relatively independent of medium when the effects of nitrate and chloride complexing were taken into account. The average values obtained for these constants are ∗β1= 1.93 · 10−3and∗β2= 8.6 · 10−8 \u3e∗β1= 1.93 · 10−3and∗β2= 8.6 · 10−8 . Reasonable agreement with these values was obtained when these constants were determined in seawater by accounting for the effects of chloride, fluoride and sulfate complexing