Feb., 1962
HEATOF VAI~OR~ZATION AND HEATOF FUSION OF I'J!XRIC CHLORIDE
Allen6 already pointed out that it might be assumed that the normal amine sulfate and the amine bisulfate form a comp1ctc:ly miscible ideal solution, which is analogous to the ideal solid solution of the components of a solid ion exchanger. I n that case the activities of the resin species can be represented by their mole fraction X . ' The equilibrium constants K and K, of the equilibria 2 and 2a can be given as
1
K~ = 30.5 (m01~/1.)-3
a t high acidities we find a slope X2
d log -1-x = I d log U I I , R O ~
Ks
with
=
__ 1 a1i1s04
(TOhH)BSO4 2( TOAH)~SOI (10)
= (TOAH)HSO4
+
and X(TOAH)BO~ = 1 - X
(11)
and the same relations exist for THA. Our K , can be written now as
x*
and
K , = X 2 ( ~ ~ ~ ~ ) ~ ~(9)~ C corresponding to UH~SO,X(TOAH)~~O
X(ToAH)nso4=
(i+
K4 =
219
(-)I x* -x
a
with the numerical value K~
=
11.4 (moie/1.)-3
In the THA case (Fig. 3a) only the slope 6 is found corresponding to
with the numerical value Kla = 5570 (mole/l.)-a
Plotting u'/*H~so, us. X*/(l - X) for the TOA and the TI-IA system, respectively, we find the Figs. 3 and 3a. There is again a qualitative agreement, but the form of the TOA Fig. 3 is somewhat more complicated, in agreement with the more complicated titration curve (Fig. 1). In Fig. 3 the part a t low acidities corresponds to a slope d log-
X2
1-x = 6
d log U1/*"2S0r
in agreement with an empirical constant
Discussion From the experiments and the results described above no quantitative conclusions can be drawn. The relations obtained are only empirical and will certainly have no general thermodynamic validity. The only conclusion which might be drawn is that the transition points in Fig. 2, 2a and 3 correspond to inflection points in the titration curves 1 and la. A surprising point of interest is furthermore t,he great difference in the processes underlying the distribution when benzene is replaced by kerosene as the solvent.
THE HEAT OF VAPORIZATION AND TKE HEAT OF FUSION OF FERRIC CHLORIDE BY CHARLESM. COOK,JR. PigmPnts Department, E . I . du Pont de Nemours & Co., Inc., Wilmingh, Dehurare Received June 9 , 1961
Pressures of Fe&&(g) above solutions of FeC12 in FesCls(1) were measured in the range 300-470". These data indicate vap.) = 14.6 i that above liquid ferric chloride log PFoCle(mm.) = 48.57 - 12.55 log T - 6373/T, where AHa~.~(FenC16 0.5 kcal./mole FerCle, ASsm.T(FenCle vnp.) = 24.8 f 1.0 e.u./mole FerC16. The boiling point is estimated to be 315'. The heat of fusion was measured by a drop calorimeter and found to be AHSm.,(FeCl$fusion) = 9.0 i 0.4 kcal./mole FeCla.
Introduction The currently acceptedla!b value of the heat of vaporization, 12.04 kcal./mole Fe2C16, at the accepted boiling point of liquid ferric chloride, 3 1 9 O , derives from measurements by Stirnemann2 of the total pressure within a closed bulb containing ferric chloride a t temperatures up to 493O. This thermodynamic value was calculated without correcting the observed total pressures for the sig-
nificant partial pressure of Cls present along with the FesC16(g) in the vapor space above the ferric chloride.8 The magnitude of the chlorine pressure correction to Stirnemann's data is discussed below, and the heat of vaporization of FezCls(l) is recalculated. Experimental
(1) (P) "Selected Values of Chemical Thermodynamic Properties," Circular 500,National Bureau of Standards (1952); (b) 0. Kubaschewski and E. Evans, "iMetallurgica1 Thermochemistry," 2nd Ed., John Wiley a n d Sons, New York, N. Y.,1956. (2) E. Stirnemann, Neues Jahrb. Mineral. Geol. u. PaZdontoZ.. 62A, 334 (1925).
(3) W. Kangro and E. Petersen, Z . anorg. Chem., 261, 157 (1950), corrected Stirnemann's presaures for P F ~ C and I ~for P C I ~The latter calculation, however, contained the assumption t h a t aFacil = 1, which is invalid for Stirnemann's experimenta above the FeCkFeCla eutectic temperature because of the solubility of FeClz in molten FezCls. See H. Schllfer, Z. anoru. u. a2Zeem. Chem., 266, 269 (1951).
Vapor Pressure.-Ferric chloridoferrous chloride mixtures were contained in a ca. 13-cc. cylindrical Pyrex sample
220
CHARLES M. COOIC,JR.
Vol. 66
bulb sealed to a sickle gage. Bulb and gage were placed The ferric chloride vas titrated for FeClz with KMnO., in within a close-fitting 3/4 in. i.d. X 12 in. L brass sleevc the presence of the Zimmermann-Reinhardt reagcnt. Declosed a t the bulb end by a brass platr. That cnd of tlie spite the prrraution of maintaining a Clz atmosphere during sleeve containing the inlet tube t o t h r outside shcll of the sample preparatioii the I'eC18 sam les contained 0.005-0.02 sickle gage wa.s packed with I'yrcx wool. Thc bulb-gagr- atoms Fe(l1) per atom Fe(II1). &he broken ampoule wm sleeve assembly wm inside a vertical pressur(? tube of 1 in. rcwrighcd to determine the total ferric chloride rescnt. i.d., 1/4 in. wall stainless strcl pipe heated with a iiniform To obtain the hcat content/mole FeC13,the oiserved total external winding of resistance wire covcwd with 3/4 in. of 1rt.at conlcnt must be correctrd for the heat contained by asbestos insulation. A Chromel-Alumrl thcrmocouplr 'sw (a) the Vycor ampoulc, ( b ) the 0.5-2 mole %. FcCl2 in the brought through the brms slcevc eiidplate to a thcrinowcll in sample and (c) reversal of reaction 2 . Correction (c) can be the bulb. shown to be negligible, while correction ( b ) comes to about The sicklc gage was used as a null-point pressurc indi- 1%. Correction (a) comes to much as 50% a t the lower cator, external pressure to balance the bulb prrssure being tcmperaturcs. Five drops of an empty Vycor ampoule iii supplied from an argon cylindrr, and prcwure brtlnnce being the range 230-380" werc fittrd to f 1% by signified by the closing of an electrical circiiit throiigh 1% C,(F'ycor) = 0.10 2.30 X IO-* I' ("K.) cal./"C. g. Vycor contacts at the pointers of the gagc. Thc prcssiire within the system was read, in tho iritrrval 0-2 4 atm , from a Hg Thc cvperimentally observed heat contents on any one manometer attached to the prrssure manifold. Pressures sample scatter by about zt3Y0. There is an approximately beyond this range were read from a 0-100 p.s.i.g. .Ishcroft 5% difference bctween the heat content memurod for Fegage. C13(c) and the probably more accurate valucs of Todd and Before sample preparation the bulb was baked in C1, a t Coughlin.S This a parent systematic error may be due to 300". Frrric chloride, prepared by reacting 1.5 g. of Fe error in the large fycor correction term; if 80 it will havc wire with Matheson "oxygcn-free" Clz, was sublimed in Clz littlc effcct upon the measured heat of fusion. The heat into the bulb. A weighed amount of fcrrous chloride, prc- coiitrnts of 1%in Pyrex determined a t two temperatures in viously prepared by distillation a t 950" in HCl of crude Fe- an ap aratus similar to this were found to agree with the Cl2 from Fe and HCl, W M added to the fcrric chloride. The pui& ed data'b to 1%. bulb was evacuated, heated to 200", back-filled with approximately 1/2 atm. of argon, sealed off, and assembled in the Discussion pressure tube. Stirnemann's Pressure Temperature Data.Pressures measured during the first heat-up drifted slowly with time, presumably because of reaction of FcC13with HzO Chlorine pressures generated by the equilibrium in the Pyrex. This effcct was limited to the initial few 2FeCL(c) = ZFeCl,(c) Cln(g) (1) measurements, after which the pressure measured for a given temperature WM stable over long periods of time and between 162 and 302°4-s fit, with standard deviaindependent of the direction of approach. tion s 0.19, the expression The observed pressures were taken to be the sum of P F ~ C I ~ , PFa&lg, P c and ~ The P F ~ C was I ~considered to be G ( 1 ) dT ncgligible.lb Pel,, calculated from equilibrium 2, was small In Pcl,(atm.) = 22.514 14327/T a t the FeClz concentrations employed. The inert gas eontribution was evaluated from measurements a t 200-250" 2' A C d l ) dT/y]/RT where the PCI,and P F ~ contributions ~CI~ were small and accurately known. The gas law was employed to estimate where AC,(l) = -12.4 - 0.004327' 920000/T2 Pinerta t higher temperatures; for the run with initial cal./mole '(3.' This expression indicates that XF&= ~ 0.26, Pioert= 1.372' mm.; for that with initial AHzgs.z(l) = 28.46 kcal., ASzg8.2(1) = 44.72 e.u., XF~CI, = 0.52, Pinort = 1.422' mm. Heat of Fusion.-A Vycor ampoule, 1.5 cm. d. X ca. 7cm. in agreement with the values AU298.2(1) = 27.7 l., was sealed to a vcrtical tube and dried a t 300" under kcal., AS2e8.2(1) = 46.1 e.u., predicted from the vacuum. Ferric chloride, prepared by chlorination of Fe known heats of formation and entropies of the wire (Baker Analyzed, Reagent), was sublimed in Cln into the vertical tube. When this tube was heated in an oven to reactants.lJ-10 Above solutions of FeCl2 in Fe2Clp(1) Pclr is 310°, the ferric chloride melted and ran into the ampoulc. The connection between ampoule and tube then was d r a m determined by to about 1 mm. d., and the molten FaCle cooled to room Fe2ClO(l) = 2FeC12(1) Cldg) (2) temperature over a period of about 30 min. under 1 atm. Clz. Finally, the system was closed, the Cl2 prrssure The free energy change, and thus the equilibrium reduced to ca. 90 mm., and the ampoule scaled off at the conconstant, of ( 2 ) can he calculated as a function of striction. The sample was suspended by a fine n ire mithin a chamher temperature from AFT(^) and the free energies in a 12 in. furnace constructed of 3/4 in. d . streamline Cu of fusion of the iron chlorides. tubing externally wound with Nichrome ribbon and insrilated Between 297.5-405' the solubility of FeClz in with 3/4 in. of asbestos. The chamber was 5 in. X 6 / ~in. d . Cu tubing silver soldered in the middle of the furnace and Fc2Cls(l)1iobeys the relation with removable brass top and bottom end plates. The In X F ~ = C 1.288 ~ ~ - 15522'-' (3) furnace ends were plugged with asbestos during sample heat-
+
+
