Nov., 195G
SOLUBILITY OF FERROUS AND FERRIC HYDROXIDES
1569
THE SOLUBILITY OF FERROUS HYDROXIDE AND FERRIC HYDROXIDE IN ACIDIC AND BASIC MEDIA AT &501 BY K. H. GAYERAND LEO WOONTNER Contribution from the Department of Chemistry, Wayne State University, Detroit, Michigan Received July 8, lg.56
A method was developed for the preparation in basic solution of pure ferrous hydroxide. Solubility studies on this material showed ferrous hydroxide to possess weak acidic properties. The principal reactions and their related thermodynamic constants have been determined for ferrous hydroxide. The solubility studies of ferric hydroxide indicate it to be indifferent as to either an acid or a base in that the p H of the water solutions of ferric hydroxide were not significantly different than that of pure water. This observation was further supported qualitatively by the identification of the principal species in basic Bolution as an undissociated molecule. Quantitative support is also indicated by the low value of the primary basic dissociation constant. Ferrous Hydroxide .-The hydroxide was precipitated from strongly basic solution by the addition of dilute ferrous chloride to a saturated solution of sodium hydroxide in an air-free system with vigorous stirring. The precipitate was washed repeatedly with normal sodium hydroxide (oxygen and carbonate-free) until a test for chloride ion with silver nitrate could no longer be obtained. Five additional one-liter washings with normal base completed Solubility the preparation of the ferrous hydroxide used for the soluRef. Solubility Fe(OH)s product bility studies. This technique led to the formation of a Whitman, Russelland Daviesz 6.7 X 10-6 3 X l o w r 4 coarse-grained precipitate, white by reflection and slightly Muratas 8.14 X 2 X 10-l6 greenish tinged by transmitted light. Dilutions of the 1.35 x 10-6 1 x 10-14 material were made to one-tenth molar base without eviLamb4 Shipley and McHaffieb 3.9 x 10-15 dence of darkening when maintained under an oxygen-free atmosphere. The oxide gave a negative test for residual Britton6 4.5 x 10-11 chloride. Elder? 48 x Ferric Hydroxide.-Ferric hydroxide was prepared in a Krassas 8.7 x 10-14 microcrystalline form which could be washed extensively Ardens 2 . 4 x 10-14 without undergoing peptization. The material was deposited from a dilute solution of Baker and Adamson reagent Schragerlo 7.0 x 1 0 - 1 3 nitrate nonahydrate by a process of hydrolysis. The Solubility product of solution was maintained a t the boiling point for a period of ferric hydroxide several weeks, the volatile components being replaced by Brittone 2 x 10-38 conductivity water. This procedure serves to drive the reaction Elder7 3 X 10-38 to 4 X 10-36 7 X 10-37 Kruikov and Awsejewitschll Fe(NO& 2H20 +FeOOH 3HN08 Bezierlz I x 10-37 toward completion. The precipitated oxide was washed by repeated decantations and introduced into the system Evans and Pryor's 3 x 10-35 together with a few drops of carbonate-free sodium hyProcedure droxide. Washing was continued with degassed conducPreparation of Reagents. Water, Sodium Hydroxide tivity water to the absence of the sodium flame test before Solutions, Perchloric Acid Solutions.-The preparations samples were prepared. The oxide was found to be free of of these substances were similar to those described by Gayer residual nitrate. and Leider .I4 Miscellaneous Analytical Reagents.-A standard iron Ferrous Chloride Solution.-J. T. Baker 99.90% iron solution was prepared from Baker A.C.S. ferrous ammonium wire, standardizing grade, was introduced into the reaction sulfate. A 0.001 molar solution of G. F. Smith reagent 4,7flask and dissolved in a volume of normal hydrochloric acid diphenyl-1,lO-phenanthroline was prepared according to insufficient to react com letely with the metal. The Smith, McCurdy and DiehP for use in the analysis of soluresultant solution was boifed free of dissolved gases and tions containing less than 10-6 mole of iron. Other cooled under pure nitrogen. A small amount of sodium reagents used in the colorimetric procedure, hydroxylamine hydroxide was introduced to increase the pH to some value hydrochloride, sodium acetate and chloroform, were prewhich would result in the complete precipitation of any pared and/or purified as specified by the above authors. ferric ion as well as a partial precipitation of ferrous hy- A 10% solution of G. F. Smith reagent 1,lO-phenanthroline droxide. The supernatant iron I1 chloride solution was was used as described by Fortune and Mellon" for the filtered into the reaction flask through a fine glass frit. analysis of solutions containing larger amounts of iron. Preparation of Samples, Equilibration of Samples, Acid (1) From a dissertation submitted by Mr. Leo Woontner in partial and Base Analysis.-The procedures were similar to those of fulfillment of the requirement@for the Doctor's degree at Wayne State Gayer and Leider.14 University. Iron Analyses (Colorimetric).-A model B Beckman spec(2) W. G. Whitman R. P. Russell and G . H. B. Davies, J . A m . troDhotometer was used for the analvsis of the eauilibrated Chem. Xoc.. 47, 70 (1925). solitions. Two methods were used to d e t e h i n e the (3) K. Murata, J . SOC.Chem. Ind. Japan, 36, 523 (1932). concentration of dissolved iron. The colored complex (4) A. B. Lamb, J . A m . Chem. Xoc., 32, 1214 (1910). formed with ferrous iron by 1,lO-phenanthroline served for (5) J. W. Shipley and I. R . McHaffie, Can. Chem. Met., 8 , 5 , 121 solutions which contained iron at concentrations greater (1924). than 10-8 molar. The analytical procedure is described by (6) H.T.8. Britton, J . Chem. Xoc., 127, 2148 (1925). Fortune and Mellon.16 (7) L. W. Elder, Trans. Electrochem. SOC.,57, 383 (1930). Solutions of ferric hydroxide obtained at equilibrium (8) P. Krassa, Z.Eleklrochem., 16, 491 (1909). pH values greater than 4 were too dilute to be analyzed (9) T. V. Arden, J . Chem. SOC.,882 (1950). with the foregoing reagent. A substituted compound, (10) B. Schrager, C022. Czech. Chem. Comm., 1, 275 (1925). 4,7-diphenyl-1 ,lo-phenanthroline, develops a similar colored
The purpose of this investigation was to obtain data on the equilibria of ferrous hydroxide and ferric hydroxide in dilute perchloric acid and sodium hydroxide solutions. Previous work is incomplete and lacking in agreement as evidenced by the following
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(11) P.A. Kruikov and G . P. Awsejewitsch Z . EZeLtrochem., 39, 884 (1933). (121 D. Bezier. Ann. Chim., 20, 161 (1945). (13) U. R. Evans and M. J. Pryor, J . Chem. Xoc.. SI57 (1949). (14) I
