The Hydrolysis and Fluoride Complexation Behavior of Fe(III) at 25°C and 0.68 Molal Ionic Strength

Fe(III) hydrolysis and fluoride complexation behavior was examined in 0.68 molal sodium perchlorate at 25°C. Our assessment of the complexation of Fe(III) by fluoride ions produced the following results: logFβ1 = 5.155, logFβ2 = 9.107, logFβ3 = 11.96, logFβ4 = 13.75, where logFβn = 5.155=[FeF (3-n)+n ][Fe3+]−1[F−]−n. The stepwise fluoride complexation constants,FK n+1, obtained in our work (where logF K n+1 =logFβn) indicate that K n+1/K n =0.072±0.01. Formation constants for equilibria, Fe3++nH2O⇌Fe(OH) (3−n)+ n +nH+, expressed in the form β *n [Fe(OH) (3-n)+n ][H+]n ,[Fe 3+]-1, were estimated as β *1 = −2.754, and β *2 ≤ −7. Our study indicates that the results of previous hydrolysis investigations include very large overestimates of Fe(OH) +2 formation constants