Some Ferric Halide Complexes, and Ternary Complexes With Thiocyanate Ions

Abstract

A spectrophotometric study of solutions containing ferric and bromide ions; ferric, bromide, and thiocyanate ions; and ferric, chloride, and thiocyanate ions is reported. The measurements were made a t constant temperature and ionic strength. The data were interpreted with the help of the results from the first paper of this series. The data sho~v that FeBr++ and FeBrz+ are formed, and values are obtained for the equilibrium constants for their formation from simple ions, and for theextinction coefficients of FeBr++. When thiocyanate is also present, the data can best be interpreted by assuming that FeSCNBr+ or FeSCNCl+ is formed. A t high chloride concentrations it seems necessary t o postulate also FeC12+ and FeSCN.CI2. Estimates are made for the equilibrium constants for the formati011 of all these species from simple ions. As with the corresponding sulphate complexes, there seems to be no particular reluctance t o form mixed complexes such as FeSCNCI+, as compared with the 'simple' complexes such as FeC12+.In the second paper of this series ( 3 b ) , results were reported which showed that the color of ferric thiocyanate could only be used as a means of investigating complexes of ferric and sulphate ions, if allowance were made for the presence of species containing ferric, sulphate, and thiocyanate, such as FeS04 .SCN. The present work deals with a similar investigation of solutions containing chloride or bromide ions, instead of sulphate. The intention was t o make a critical examination of this method of investigating ferric complexes, and in particular t o discover t o what extent ternary complexes, such as FeSCN.Cl+ or FeSCN.Br+, were important. Rabinowitch and Stoclcmayer have already investigated solutions containing ferric and chloride or bromide ions, but not thiocyanate as well (6). They suggested that the discrepancy between their result for the equilibrium constant for the formation of FeCl++, and the earlier results of Bent and French (I), who examined solutions made from ferric chloride and potassium thiocyanate, was due t o the ion FeSCN.Cl+. The present work attempts a more quantitative estimate of the formation of this ion, and of the analogous FeSCN.Br+. I t is believed that the results demonstrate the existence of these ions, and values for the equilibrium coilstants of their formation from simple ions have been obtained. APPARATUS A N D MATERIALSAll optical measurements were made with a Beclcmann Model DU spectrophotometer, modified so t h a t the temperature of the solutions could be controlled, as described in the first paper of this series (3a).T h e reagents used were the same as described in this same paper, with the following additions.Hydrochloric acid.-The concentrated reagent grade acid was diluted t o give a stock solution of about 1 M concentration. This was standardized volumetrically against borax.'Manuscript

Thermodynamics and kinetics of aqueous iron(III) chloride complexes formation

“…in which expression & is the overall concentration change for the step i. & is related to the equilibrium concentrations of the species and to the change of the equilibrium constants by the system of equations shown in eq 24 which can be derived using the law of mass action and the principle of mass conservation for the chloride and the ferric ion.…”

Some Complexes Present in Aqueous Ferric Chloride Solutions

“…This note describes an improved method for the preparation of a stable Fremy's salt, Kz[ON(S03)2], which has been used as an analytical tool for estimating free phenolic hydroxyl groups in isolated lignin (I) and also in lignins present in groundurood pulp (2,3). The usual methods (4-10) for its preparation consisted essentially in preparing the sodium or potassium salts of hydroxylainine disulfonic acid follo\ved by oxidation with either lead oxide, silver oxide, or potassium perinanganate.…”