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

Alan L. Soli, Robert H. Byrne

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Abstract

<p> Fe(III) hydrolysis and fluoride complexation behavior was examined in 0.68 molal sodium perchlorate at 25&deg;C. Our assessment of the complexation of Fe(III) by fluoride ions produced the following results: log <sub> F </sub> &beta; <sub> 1 </sub> = 5.15 <sub> 5 </sub> , log <sub> F </sub> &beta; <sub> 2 </sub> = 9.10 <sub> 7 </sub> , log <sub> F </sub> &beta; <sub> 3 </sub> = 11.96, log <sub> F </sub> &beta; <sub> 4 </sub> = 13.7 <sub> 5 </sub> , where log <sub> F </sub> &beta; <sub> n </sub> = 5.15 <sub> 5 </sub> =[FeF <sup> (3-n)+ </sup> <sub> n </sub> ][Fe <sup> 3+ </sup> ] <sup> &minus;1 </sup> [F <sup> &minus; </sup> ] <sup> &minus;n </sup> . The stepwise fluoride complexation constants, <em> F </em> K <sub> <em> n </em> +1 </sub> , obtained in our work (where log <sub> F </sub> <em> K </em> <sub> n+1 </sub> =log <sub> F </sub> &beta; <sub> n </sub> ) indicate that K <sub> <em> n </em> +1 </sub> /K <sub> <em> n </em> </sub> =0.072&plusmn;0.01. Formation constants for equilibria, Fe <sup> 3+ </sup> +nH <sub> 2 </sub> O&rlhar;Fe(OH) <sup> (3&minus; <em> n </em> )+ </sup> <sub> <em> n </em> </sub> + <em> n </em> H <sup> + </sup> , expressed in the form &beta; <sup> * </sup> <sub> n </sub> <em> [Fe(OH) </em> <sup> (3-n)+ </sup> <sub> n </sub> ] <em> [ </em> H <sup> + </sup> ] <sup> n </sup> <em> ,[Fe </em> <sup> 3+ </sup> ] <sup> -1 </sup> , were estimated as &beta; <sup> * </sup> <sub> 1 </sub> = &minus;2.754, and &beta; <sup> * </sup> <sub> 2 </sub> &le; &minus;7. Our study indicates that the results of previous hydrolysis investigations include very large overestimates of Fe(OH) <sup> + </sup> <sub> 2 </sub> formation constants.</p>
Original languageAmerican English
JournalJournal of Solution Chemistry
Volume25
DOIs
StatePublished - Jan 1 1996

Keywords

  • Iron(III)
  • ferric
  • hydrolysis
  • fluoride
  • complexation

Disciplines

  • Life Sciences

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