Sept ., 1961
REACTION OF
FEBRIC CHLORIDE WITH SODIUM AND POTASSIUM
CHLORIDES
1505
hydrogen is formed from recombination of two that the rates of reactions (1) and (11) are of thc hydrated electrons in the water (cf. reaction 1) same order of magnitude but that as a result of reaction (12) the dimensions of the spurs are in€LOHzO-- +Hs + 20H(11) creasedI8 and the probability of like-species reI n acid solution the hydrated electrons can, in the combination reduced. absence of other solutes with which it can react NOTEADDED.-The results by Mahlman ( J . Am. directly an H20-,16,i7 be converted to H atoms Chem. SOC.,81, 3203 (1959)) on the determination H20H" ---+H 4- Hz0 (12) of C(WJ from air-free Ce4+solutions were brought which would then have to recombine to give to the attention of the author, after submission of molecular hydrogen (reaction 1). Ce4+ions pres- this paper. It does not seem possible to account ent in solution could be expected to compete for the disagreement in our values for G(H2). with the hydrogen ions for reaction with the hyAcknowledgment.-The author wishes to thank drated electrons. I n order to explain the decrease Drs. A. 0. Allen and H. A. Schwarz for many disof GI*, with increase in the [H+i it is possible that cussions and valuable suggestions in connection either the H atoms recombine (reaction (1)) more with this work. slowly than hydrated electrons (reaction (ll)),or (18) B. A. Schwarz, J. hl. Caffrey, Jr., and G. Scholes, J. Am. Chem.
+
+
(17) E. Rayon and J. Weiss, J . Chem. Soc., 5091 (1960).
Soc., 81, 1801 (1959).
THE REACTION OF FERRIC CHLORIDE WITH SODIUM AKD POTASSIUM CHLORIDES BY CHARLESM. COOK,JR.,AND WENDELL E. DUNN,JR. Pigments Department, E. I . du Pant de Nemours & Co., Inc., Wilmingtan, Delaware Received February 9, 1981
The equimolar complexes of FeC13 with NaCl and KC1 have been studied by phase behavior, X-ray diffraction, thermochemical and vapor pressure methods. The phase diagrams show double eutectics, the FeC13-NaCl system a t X N & C=L 0.48 and 0.51, and FeC13-KC1 a t X K C=~0.45 and 0.52. The standard heat of the reaction NaCl FeCls = NaCl.FeC13 a t 25' is -0.8 kcal./mole; that to form KCl.FeC13 is -7.2 kral./mole. The temperature and composition dependence of ferric chloride pressure above its mixtures with NaCl and HC1 indicate the 1:1 complexes to be stable in the melt and to be as M +FeCla-. Evidence is presented for the existence of NaC1.FeCls and KCl.FeCla in the vapor phase.
+
Introduction Ferric chloride is known to form 1:l addition compounds with molecules capable of supplying a chloride ion, e.g., with Et&C1,1 NH4Cl,2 TICl,3 XOCl,4 CKCl16Poc13,6 PC15.7 These compounds are regarded as containing the [FeC4]- ion; their solutions in non-aqueous solvents are electrically conducting, and electrolysis of FeC13 in CNCl transports Fe t o the anode.5 Two previous studies of the FeC13-SaCI phase diagram have indicated a single eutectic, without evidence of compouiid Although the vapor pressure of ferric chloride is strongly reduced in the presence of sodium chloride, Johnstone, et a l l 8 ~ h determined o the ferric chloride pressure above melts containing up to 46 mole yo KaC1, explained this reduction as the normal effect of the solute in lowering vapor pressure and found no evidence for the existence of a compound. This explanation, however, is not compatible with the ob(1) V. Gutxnann and F. hfairingzr, 2. anorg. allgem. Chem., 289, 279 (1957). (2) K. Hachmeister, Z.nnorg Chem , 109, 145 (1919). (3) G. Scarpa, Attz Acad. Lancet, (51 21, 720 (1912). (4) J. Lewis and 13. B. Sowerly, J. Chem. Soc., 1617 (1957). (5) A . A . Woolf, abzd., 252 (1954). ( 6 ) V. V. Dadape and M. R. A . Kao, J. Am. Chem. SOC.,77, 6192
(1955). (7) Ya. A. Fiaikov and Ya. B. Burdanov, Doklady Akad. A'auk S.S S.R., 92, 585 (1953). ( 8 ) €1. F. Jol~nstone.H. C. R-eingartner and W. E. Winsche, J . Am. Chem. SOC.,0 4 , 2 4 1 (1942). (9) I. S Moxonov and D. Ya. Toptygin, Zhur. N e o r p . Khzm , 2 , 2 1 2 9 (1957).
servation by Dunn'O that, below 400°, the ferric chloride pressure drops rapidly to nearly zero at 50 mole % XaC1. In the chemically similar system NaCI-AlC13 both the vapor pressure" and phase diagramI2 data are consistent in indicating the KaA1C14 compound. Experimental Sample Preparation.-Two alternate procedures for preparation of FeCl8-KaC1 melts were employed. Those FeC13-NaC1 mixtures having less than 50 mole % ' SaCl that were used in measurement of the ferric chloride vapor pressures were prepared by mixing FeC13 (B & A Code 1733 Sublimed Technical) and XaC1 (B B: -4,C.P.). The resulting mixture was treated with COClz for several days t o remove traces of ferric oxide before vapor pressure measurements were carried out. Melt compositions were determined a t the beginning and end of each vapor pressure run by sampling and analysis. The ferric chloride-alkali chloride melts used for the remaining vapor pressure, the phase diagram, and the calorimetric studies were prepared in the following manner. Alkali chloride was added to the bulb which was to contain the salt mixture. Air was removed by evacuation and back filling with Clz, and the Ealt was warmed t o 300". Iron mire, contained in a side tube attached to this bulb, was burnt in a stream of chloride, and the ferric chloride sublimed into the salt. The traces of iron and alkali chloride carried by the chlorine from the pot during sample preparation were trapped in a Pyrex wool plug located before the exit bubbler and were determined by analysis. The melt (10) W. E. Dunn, Jr., presented at A.C.S. Delaware Valley Regional Meeting, Feb. 16, 1956. (11) E. W. Dewing, J . Am. Chem. Soc., 77, 2639 (1955). (12) U.J. Shvartsman, Zhur. Fk. Khim., 14, 254 (1940).
CHARLLS 11. COOK,JR.,AND WENDELL E. DUNN,JR.
1506
compositions were determined from the %-eights of salt and iron put into the mixture. The sodium chloride and potassium chloride were purified by fusioii in HCl and were crushed and stored under a dry atmosphere. The iron wire was Baker Analyzed reagent grade; tlne chlorine was Matheson "oxygen-free." I n subsequent discussion where melt compositions are expressed as mole fraction of alkali chloride, MC1, this is an input or nominal mole fraction; X ~ c l= N input MCl/.V input MCl N input FeC13. The mole fractions of MFeC14, on the other hand, are believed t o represent the actual concentrations of hIFeCll in the melt and are calculated presuming reaction 2 t,o be quantitative. I n MC1-rich melts X D I F = ~C Ar ~ input ~ FeC13/W input MCl. Phase Diagrams.-The salt mixtures used in the phase studies vere prepared in 30 mm. d. by 4" Vycor bulbs and m-ere sealed off under a C12 pressure of 90 mm. The bulbs were then placed inside a cavity, formed of "TIPERSUL" insulation, inside B 7" length of 2.5" d. heavy wall steel pipe located within a I\-ell-insulated tube furnace. Agitation of the molten mixture was provided by rocking the tube furnace. The transition temperatures of the salt mixtures were determined from their cooling curves. Salt temperatures were measured by a Chromel-Alumel thermocouple, which had been standardized previously against the melting point of bismu.th, located in a well along the axis of the bulb. The phase transitions were located by following the temperature differential between sample and surrounding pipe, measure3 by two pairs of Chromel-hlumel thermocouples, on a Miiineapolis-Honeywell Brown recorder. Changes in cooling rate appeared as sharp discontinuities in the slope of the differential temperature us. time plot. Transformation temperatures measured by t'his method were reproducible to &lo below 250" and t o & 2 O for higher temperatures. X-Ray Powder Patterns.-Mixtures of SaCl-FeCla and KC1-FeC13 were taken from t'he sample bulbs after cooling curves Tvere run, glound in a dry box and loaded into 0.5 nim. Lindemann glass capillaries and exposed t o iron filtered 35 Kv. cobalt radiation for four hours in a powder camera. The D spacings were read from the Debye-Scherrer photographs with a M e s scale, and the intensities of the lines were estimated visuali).. Caloriinetric Measurements.-The solution calorimeter was a one-liter Deivar flask closed with a cork through which were brought a Beckmann thermometer, a stirrer, and tube for introducing samples. The calorimeter contained 800 cc. of HC1 SaCl KC1 solution in which t'he ferric chloride-containing salts Tyere readily soluble. The water equivalent of the calorimeter plus t'he solution was measured by observing the t'emperature rise per watt minute passed through a resistor inside the calorimeter. Approximately 10-g. samples of SaC1, KC1, FeCI3, NaFeCI4 and IIFeC14 vere loaded in a dry box into glass bottles which vere then paraffined and stored in a desiccator unril use. The FeCls had been purified by sublimation in (312; the SaFeC14 and KFeC14 had been prepared and used in tbe phase studies. These salts mere stored in sealed bulbs until this use. A sample bottle was 1%-eighed,the calorimeter entry tube unstoppered, the sample quickly uncapped and dumped through t'he tube into the HC1 solution, the calorimeter closed and the emptied bottle reveighed. In this process the salts were exposed to the atmosphere for less than three seconds. Heats of solution were determined from the temperature change. The calorimeter was operated near room temperature; thus corrections for the sensible heat, introduced n-ith the salt were small. hIeasured heats of solution were in 4.92 i ! HC1 KaC1 := -2.2 lrcal./rnole KC1 = -4.0 kcal./mole F'eCl:< >= 20.8 kcal./niole SaFeC1, = 18.1 kcal./mole lIFeCII = 9.6 kcal./mole iii 6.J4 .\ FTCI, 0.125 "V XaCI) 0.125 ,VKCI S a C l := -2.3 kcal./niole IiCl = -3.9 Ircal./niole FeClp := 18.8 kcal./mole SaFeCl4 = l j . 6 kcal./mole
+
+
I\I:cC!j
=
+
ii.8 k c n l . 'ino!c
T'ol. 6.5
Heats of fusion and heat capacities were determined in a drop calorimeter constructed in the same fashion as the solution calorimeter except that the entry port was replaced by a Pjrrex test-tube and the calorimeter contained H20 rather than HC1 solution. The test-tube, extending into the water, was padded on the bottom with a plug of Pyrex wool and contained 10 cc. of silicone oil to facilitate heat transfer. The sample was sealed into a Pyrex ampoule and this was suspended by a fine copper wire inside a tube furnace. The sample temperature was measured with a ChromelAlumel thermocouple placed in a thermocouple well extending about three-quarters of the way into the ampoule. The tube furnace was constructed of an electrically heated, asbestos-jacketed, 3/4" by 11" 1. copper pipe. The top of the furnace was sealed m-ith an asbestos plug through which passed the sample thermocouple and the copper wire suspending the ampoule. I n the region of the sample the furnace wall temperature was uniform t o 1 2 . When the sample had come to constant temperature, the. tube furnace was swung into position over the calorimeter, an aluminum radiation shield removed, and the sample dropped into the test-tube by cutting the copper wire. The furnace then >vas removed and the test-tube corked. Because of the short time of exposure and the relatively low temperatures employed, radiative heat transfer from the furnace t o the calorimetric during the release of the sample was not significant. The heat content, of the Pyrex in the ampoule x a s calculated assuming that for Pyrex C, = 0.20 cal./g. For calibration, the heat contents of a sample of bismuth were determined a t two temperatures using the drop calorimeter with the above procedure. Temp., 'I
