Preparation and Analysis of Barium Ferrate(V1) J. R. GUMPI, W. F. WAGNER, and J. M. SCHREYER2 D e p a r t m e n t c f Chemistry, University o f Kentucky, Lexington, K y .
Methods are described for the preparation and analysis of barium ferrate(V1). Barium chloride dihydrate is added to potassium ferrate and barium ferrate is obtained as a maroon precipitate, 86.5Yo pure. The chromite method for analysis of soluble ferrates has been modified for application to insoluble barium ferrate.
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'NT interest in the use of the ferrate ion as :t strong oxidizing agent has led to a n investigation of the preparation of various ferrate compounds. The availability of relatively pure potassium ferrate ( 5 ) made it the logical starting material for the preparation of barium ferrate. The addition of a soluble barium salt to a solution of an alkali nietal ferrate produces a n insoluble maroon precipitate of barium ferrate which has the crystalline form of barium chromate and :tpproximately the same solubility. Several investigators ( 1 - 3 ) have reported the preparation and properties of barium ferrate. However, they gave little attention to the effects of teniperature and the prolonged washing, filtering, and exposure of the precipitate t o carbon dioxide. I n many of the experiments, alkaline solutions of the alkali metal ferrates mere used, which led to precipitates of barium ferrate contaminated with barium hydroxide and barium carbonate. Other important factors influencing the stability of aqueous ferrate solutions, and thus their purity, are temperature (6) and exposure to carbon dioxide.
A 0.1- to 0.2-gram sample of barium ferrate iyas added to a mixture containing 20 ml. of saturated sodium hydroxide, 3 ml. of chromic chloride solution (25 grams of chromic chloride hexahydrate in 150 ml. of water), and in some cases 3 grams of sodium carbonate decahydrate. This mixture was allowed to stand 15 minutes to permit any initial reaction t o proceed. Then 50 ml. of water were added and the mixture was heated for 1 or more hours a t 95" to 100" C. on a hot plate. T h e mixture was cooled in a n ice bath and then acidified with a mixture of sulfuric and phosphoric acids (60 ml. of concentrated sulfuric acid and 150 ml. of 85% phosphoric acid in 240 ml. of distilled water). The resulting dichromate solution was titrated with a standard ferrous ammonium sulfate solution using sodium diphenylamine sulfonate as the indicator. The precipitate of barium sulfate which formed on acidification did not interfere with the visual end point nor was there evidenre that coprecipitat'ion of chromate ion materially affected the results. A blank was carried through the entire procedure, including heating time, and the correction was apy lieti to the analysie. The results of these experiments for the analysis of a sample of barium ferrate are shown in Table I. The addition of sodium carbonate had no significant effect up011 the analysis. -4 heating time of 2 or more hours was required t o give consistent results. A blank correction is necessary because a small amount of the chromite ion is apparently oxidized h y oxygen from the air during the heating period. T o check the validity of the method, a sample of potassium ferrate analyzed b y the modified chromite method gave a value of 75.3% as compared with i5.7% by t'he rcgular chromite method
(4). PREPARATION
Preliminary experiments indicated that the purity of barium ferrate could be improved by carrying out the reaction a t a low temperature in the absence of carbon dioxide and by filtering and drying the precipitate rapidly. T h e best samples of barium ferrate were prepared by dissolving 1 to 2 grams of potassium ferrate and a sufficient quantity of barium chloride dihydrate to react therewith in ice-cold, carbon dioxide-free distilled mater. T h e solutions were mixed and the maroon precipitate which formed was separated by filtration through a cooled fritted-glass funnel under a nitrogen atmosphere. The precipitate was dried overnight in a vacuum desiccator a t a pressure of 4 to 5 mm. of mercury. Barium chloride was preferable to barium nitrate because its greater solubility permitted the use of smaller quantities of water for the reaction. ANALYSIS
Several methods for the analysis of barium ferrate were attempted before a successful one was found. These included analyses based upon the oxidation of the oxalate ion and ferrous ion in acid solution by the barium ferrate, the determination of the total iron in the sample, and iodometric procedures. The most successful method developed was a modification of the chromite method ( 4 ) used for the analysis of soluble ferrates. This method is based on the determination of the amount of chromate formed from the oxidation of the chromite ion, in a strongly alkiline solution, b y barium ferrate. The insolubility of barium ferrate made it necessary to investigate various factors t h s t might influence the reaction between the precipitate and chromite ion.
Table I. Analysis of Barium Ferrate by the Modified Chromite Method Expt. NO.
SazCO8.10 H20 Added, Grams
Heating Time, Hr.
BaFeOa, 81.3 81.1 81 2 81.0 80.9 80.5
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The procedure described above, with a heating time of 2.5 hours and without the addition of sodium carbonate, wab used for the analysis of the samples of barium ferrate. Triplicate determinations of the purity of the best sample of barium ferrate were: 86.5, 86.1, and 87.0%, giving an average of 86.5%. The chief impurities in the winple consisted of h i drous ferric oxide and bnrium rarbonatp. LITERATURE CITED
(1) Losana, L., Gazz. chzm. zlal., 55, 488 (1925) (2) . , Mellor. J. W.."Comorehensive Treatise on Inornanic and Theoretical Chemistry,;' Vol. XIII, London, Sew'k-ork , Toronto, Longmans, Green 8: Co., 1934. (3) LIoeser, L., J . prakt. Chem. (2), 56, 425 (1897). (4) Schreyer, J. M., Thompson, G. W., and Ockerman, L. T., ANAL. C H E W , 22, 1426 (1950). (5) Thompson, G. W., Ockerman, L. T., and Schreyer. J. SI..J . Am; Chem. SOC.,73, 1379 (1951). (6) Wagner, IT. F., Gump, J. K., and Hart, E. S . , ANAL.CHPM., 24, 1497 (1952).
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Present address, Michigan Chemical Corp., St. Louis, Mich. Present address, Oak Ridge National I.aboratory, Oak Ridge, Tenn.
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RECEIVED for review June 4, 1952. .4ccepted July 26, 1954.
1957
