William B. Guenther University of the South Sewanee, Tennessee
The Diisopropyl Ether Extraction of lron(lll) Chloride
The diisopropyl ether extraction of iron(111) from 8 d l HCl solution (1, 2) is a simple method of separating iron from the other components of stainless steel alloys. The extraction and subsequent homogeneous precipitations of F d W a and nickel dimethylglyoximate make a valuable introduction to these ideas. With high percentage iron samples, a third phase is sometimes noticed. Honors student Alan ~ a r l i n ~ t owas n curious about this third phase and performed the experimental checks described here. A ~ a r t i a explanation l can be found in references (1) and (3). A solid compound is reported of composition HFeC18:2(isopropyl ether) which is insoluble in the ether under anhvdrous conditions. From 8 A f HCI. the species extracted a t low iron(II1) concentration; is this dietherate with five water molecules associated with it. With higher iron(II1) and HC1 concentrations, a third layer forms consisting of ether saturated with the dietherate and fewer than five water molecules per iron(II1). This ether phase is green and lies between the aqueous HC1 and the light ether phase. This causes no trouble in the quantitative separation, since both upper layers contain the extracted iron and can be stripped with water for iron determination.
Demonstration
The unusual formation of three phases from two liquids can be demonstrated with the following mixture: 1.5 g FeC18, 50 ml 8 d f HCl, 40 ml diisopropyl ether.' Mix well and put into a 100-ml graduated cylinder. The relative volumes of the phases show that both upper layers must be ether phases. Addition of 10 ml of water takes the system below the consolute point, about 7 M HCI (4), where only two phases then exist. (This water must not be added in quantitative extraction.)
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Used ether e m be stored over acidified 30% FeSO. solution for future use. Dry ether starage can be very dangerous, qf. THISJOTJRNAL, 41, A575 (1964).
Estimotion of Iron
The three-phase behavior allows a very quick estim* of iron(III), At a given temperature and pressure in this four component system, the phase rule allows one degree of freedom, ~ hat a~fixed~H C,molarity, ~ the collcentration of iron(lll) in each ether phase is invariant with;n the two-ether-phase region. F~~~ the phase diagwm (4), at 7.5 HC1 (8,8 molal), the lower ether phase contains 0.42 M iron(III), and the upper, 0.06 M. For example, 23 ml of diisopropyl ether are required to produce the first bit of the light ether phase over an iron sample in 7,5 HC1, This gives (23 m1)(0.42 M )(162 mg FeC18/m mole) = 1570 mg FeClr A 1.5 g sample of FeCla had been taken for this trial. A stoppered graduated cylinder for extraction permits rapid estimation of iron(II1). Amounts from 20 to 1000 mg would take about 1 to 50 ml of the ether. If the light ether phase is produced in volume greater than 10% of the heavier one, the total iron in both phases can be calculated. A minimum volume of 7.5 M HC1 should be used to contain the sample. The method might be capable of refinement for greater accuracy. This would make an interesting student project. I n the quantitative chemistry course, the iron(II1) extraction is followed by homogeneous precipitations of Fe(OH)8 (5) and nickel(I1) (6). Literature Cited (1) DODSON, R. W., FORNEY, G. J., AND SWIFT,E. H., J. Am. Chem. Soc., 58, 2573 (1936). (2) CHARLOT,G . AND BEZIER,D., "Quantitative Inorganic Analysis," John Wiley and Sons, Inc., New York, 1957, pp.
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(3) LAURENE, A. H.,CAMPBELL, D. E., WIBERLEY, S. E., AND CLARK,H. M., J . Phys. Chon., 60, 901-4 (1956). (4) MYERS,R. J., AND METZLER, D. E., J. Am. Chem. Soc., 72, 3772-6 (1950). , . (5) WILLARD, H. H.,FURMAN,N. H., AND BRICKER,C. E., "Elements of Quantitative Analysis," 4th ed., D. Van Nostrand, Inc., Princeton, N. J., 1956, p. 341. (6) VOGEL,A. I., "Quantitative Inorganic Analysis," 3rd ed., John Wiley and Sons, Inc., New Yark, 1961, p. 527.
Volume 42, Number 5, May 1965
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