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 ${}^1\text{β}{}_1\text{and}{}^1\text{β}{}_2$ 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 ${}^1\text{β}{}_1\text{= 1.93 · 10}{}^{\mathrm{?3}}\text{and}{}^1\text{β}{}_2\text{= 8.6 · 10}{}^{\mathrm{?8}}$. 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.