802
JAMES L. BILLSAND F. ALBERTCOWON
The Heat of Formation of Germanium Dioxide'
by James L. Bills2 and F. Albert Cotton3 Department of Chemistry, Maasachueetts Imtdute of Technology, Canbridge 39, Massaehueetta (Received Odder IO, 1963)
A new procedure has been used to measure the standard enthalpy of formation of hexagonal germanium(1V) oxide, GeO2(c, I), affording the value -132.2 f 1.2 kcal./mole. This agrees very well with the result obtained by Yokokawa, el al. (-132.3 f l.O), and one which can be calculated from data of Jolly and Latimer (- 132.6 f 2.0), but differs by 3.9 kcal./mole from the value, based on combustion data, listed in the National Bureau of Standards Tables (- 128.3 kcal./mole).
Introduction In the course of some thermochemical studies of organogermanium compounds, reported elsewhere, we became aware of some discrepancies and consequent uncertainty about the heat of formation of germanium(IV) oxide. Since this quantity plays a role in the interpretation of our data, and will do so in other thermochemical studies of germanium compounds, a reinvestigation of the heat of formation of GeOz was carried out and is reported here. The value of - 128.3 kcal./mole listed in the National Bureau of Standards tables6 for AHr" (GeOz, amorphous) is based upon two determinations of the heat of combustion of elemental germani~m.~.' I n both determinations, errors may possibly have been introduced by incomplete combustion and by the reaction of the Ge02 with water, which was either introduced deliberately or formed by combustion of paraffin oil used as a combustion aid. Other difficulties are also encountered in this direct combustion method.s#8 Later, Jolly and Latimere measured the heats of solution of Ge(c) and of GeOz(c, I) in basic hypochlorite solution, obtaining for AHf" of GeO2(c, I) the value -129.2 f 2.0 kcal./mole, which was considered to confirm the value derived from the combustion data. However, they used -24.5 kcal./mole for A H r O of aqueous hypochlorite ion, whereas a more recent determination'O yields - 26.2 kcal./mole, thus leading to a AHto for GeOn(c,I) of -132.6 f 2.0 kcal./mole, which does not agree satisfactorily with the combustion result. The Journal of Phg&
Chemistry
Still more recently, a group of Japanese investigators" carefully measured the equilibrium
Ge(c)
+ 2HnO(g) = GeO& 1) + 2Hdg)
between 500 and 650", from which data they calculated -132.3 =k 1.0 kcal./mole for AHf" of GeO2(c, I) at 25". They give reasons for believing that their result is more reliable than that (- 141.8 kcal./mole) obtained in an earlier studyI2 of the same equilibrium by a different method. While their result agrees ~~
~
(1) This work wm supported in part by the National Science Founda-
tion and by the donors of the Petroleum Research Fund, administered by the American Chemical Society, to whom grateful acknowledgment is made. (2) Standard Oil of Ohio Fellow, 1960-1961; National Science Foundation Cooperative Fellow, 1961-1962. (3) Alfred P. Sloan Foundation Fellow. (4) J. L. Bills and F. A. Cotton, J . Phys. C h . ,68,806(1984). (5) F. D. Roasini, et ol., "Selected Values of Chemical Thermodynamic Properties," National Bureau of Standards Circular 500, U. 9. Govt. Printing Office, Washington. D. C., 1952. (6) G. Becker and W. A. Roth, 2. phyeik. Chem., A161, 69 (1932). (7) H. Hahn and R. Juza, 2.anorg. Chem., 244, 120 (1940). (8) Although it is stated' that about two thirds of the GeOn was the hexagonal modification, the N.B.S. tables assign the AHfO value to amorphous (or glassy) Ge09. In this paper we shall follow the established nomenclature in which the hexagonal and tetragonal forms of Ge01are denoted GeOz(c. I) and Geode, II), respectively. (9) W. L. Jolly and W. M. Latimer, J . Am. Chem. SOC.,74, 5757 (1952). (10) J. E. McDonald, J. P. King, and J. W. Cobble, J . Phys. Chem., 64, 1345 (1960). (11) T. Yokokawa, M. Koizumi, iM. Shimoji, and K. Niwa, J . Am. Chem. Soc., 79, 3365 (1957). Y. Inada, and I. Konno, BUU. Rea.Imt. Mineral Dressing (12) K. 0x10, Met., 11, 169 (1955).
HEATOF FORMATION OF GERMANIUM DIOXIDE
803
Table I : Data F'ertaining to Calibration of CaIorimeter Final
Moles
Run
temp.,
-4Hm
of acid
no.
O C .
cal./mole
neutralized
1 2 3 4
24.84 24.82 25.01 25.08
14,394 14,394 14,290 14,130
0.25028 0.24967 0.25022 0.25000
Calories evolved
3,602 3,594 3,576 3,532 Mean value of &&I:3,321 Std. dev. of the mean: 1 . 1
well with that recalculated from Jolly and Latimer's measurements, the difficulties of the high temperature measurements raise some concern as to the certainty of that result, although, as will be seen, the result is indeed quite accurate. In the course of OUR: studies with germanium compounds, it was observed that both germanium and GeOz can be dissolved fairly rapidly in a solution of hydrogen peroxide and hydrofluoric acid. 'These reactions were used for B new and independent determination of AH*' for GeOa(c,I).
Experimental Apparatus. The rotating-bomb calorimeter described elsewhere4 was used. In order to use it as a heat of solution calorimeter with hydrogen peroxidehydrofluoric acid as solvent, the usual combustion bomb was replaced by a 16-02. wide-mouth polyethylene bottle fitted with a leak-proof cap and a weighted brass sleeve, to which the gear girdle of the bomb was fitted. The tumbling motion usually imparted to the bomb immediately following combustion was then used to effect mixing and agitation of the solute and solvent. In all experiments, about 100 ml. of one solution was contained in the 16-02;. bottle, while 50 ml. of a second solution was contained in a 2-02. wide-mouth polyethylene bottle, which was covered loosely and initially stood upright in the other solution. Calibration. The energy equivalent of the calorimeter was determined using the heat of neutralization of hydrochloric acid by sodium hydroxide. The value of - 14,555 cal./mole, given by Bender and Bierrnrtnnl4 for the heat of neutralization of 4 m HCl with 4 m NaOH was used as the standard. Various corrections for heats of dilution were made by graphical interpolation of data in the N.B.S. tables6 and checked against data in the literaturelb!l6 recalculated after Bender and Biermann.14 A standard deviation of 40 cal./mole was assigned to each A H , measurement, which includes the 0.1% uncertainty assigned by Bender and Biermann
Measured 4t, deg.
E, cal./deg.
cal./deg.
1.0441 1.0420 1.0323 1.0118
3,450 3,449 3,464 3,491
3,320 3,319 3,322 3,324
&std,
to their own results. Correction of the AH, values from 25" to the actual final temperatures were made using appropriate heat capacity data from the literature. 17- l 9 Table I summarizes the calibration data. E is the energy equivalent of the initialsystem including the heat capacities of the HC1 and NaOH solutions and any excess water over the standard amount in the calorimeter can. &std is the energy equivalent of the initial system after subtraction of these three contributions. Materials. The elemental germanium was the "intrinsic metal" obtained from Eagle-Picher Co. It was crushed in a stainless steel press and ground in an agate mortar under absolute ethanol until it passed through a 200-mesh sieve, and then dried in vacuo a t 100". The oxygen content was estimated by the vacuum fusion method20as0.003%. Germanium(1Y) oxide from three different sources was tested for use. Samples from Eagle-Picher Co. and from Fisher Scientific Co. were found to be incompletely soluble in hydrofluoric acid, presumably because they contain some of the tetragonal modification.21 A third sample, which originated with the Raytheon Co., kindly provided by Professor J. W. Irvine, Jr., was found to be completely soluble. It was used for runs 1, 2, arid 5 (Table 111). The Fisher (13) A more detailed description may be found in the P h D thesis of J. L. Bills, Massachusetts Institute of Technology, 1963. (14) P. Bender and W. J. Biermann, J . Ams. Chem. Sac., 74, 322 (1952). (15) G. Akerlof and J. W. Teare, ibid., 59, 1855 (1937). (16) J. W. Bertetti and W. L. McCabe, I n d . Eng. Chem., 2 8 , 247 (1936). (17) P. T. Gucker, Jr., and K. H. Schminke, J . Am. Chem. Soc., 54, 1358 (1932). (18) J. W. Bertetti and W. L. McCabe, Ind. Eng. Chem., 28, 375 (1936). (19) L. J. Gillespie, R. H. Lambert, and J. A. Gibson, Jr., J . Am. Chem. Sac., 52, 3806 (1930). (20) A. L. Beach and W. G. Guldner, Am. SOC.Testing Mater., Spec. Tech. Publ., 222, 15 (1958). (21) A. W. Laubengayer and D. 5. Morton, J . Am. Chem. SOC.,54, 2303 (1932).
Volume 68, Number 4
A p r i l , 1966
804
JAMESL. BILLSAND F. ALBERTCOTTON
~
Table I1 : Data Pertaining to the Heat of Solution of Elemental Germanium
Wt. of Ge, g. Wt. of 15% HF, g. Wt. of 5% HzOz, g. E, cal./deg. (see text) At, deg. Q, cal. Initial moles of HF.6.294Hz0 Final mole ratio (HzO H2O2)/HF Qdiln, cal. &,or = Q - Qdiln, cal. Qeor/mole,kcal./mole
1.4518 104.20 50.93 3466.6 1,2012 4164.1 0.7811 9.827 35.9 4128.2 206.41
+
1.4528 104.02 50,77 3465.2 1.2037 4171.1 0.7798 9.823 35.8 4135.3 206.62
Mean &,,,/mole, kcal./mole: Std. dev. of the mean:
I . 4535 104.30 51.08 3465.8 1.2021 4166.2 0.7819 9.835 36.0 4130.2 206.27
1,4510 104.77 51.16 3466.3 1.1993 4157.1 0.7854 9.825 36.0 4121.1 206.17
206.37 0.10
Table 111: Data Pertaining to the Heat of Solution of Cermanium(1V) Oxide(c, I )
Wt. of GeOz, g. Wt. of 15Yc HF, g. Wt. of 2.36% HzOz, g. E, cal./deg. (see text) At, deg. Q, cal. Initial moles of HF.6.294HzO HzOZ)/HF Final mole ratio (H20 -&dilnJ cal. -Qvap, cal. Qo0,, cal. Qoor/mole,kcal./mole
+
2.0994 105.33 50.81 3467.5 0.1780 617.2 0.7896 9.826 -36.2 0.4 581.4 28.96
2.0912 104.75 50,23 3466.4 0.1770 613.6 0.7852 9.805 -35.9 0.4 578.1 28.91
Mean Qoor/mole,akcal./mole: Std. dev. of the mean: a
Results of runs 3 and 4 excluded;
2.0651 104.04 49.91 3465.4 0.1754 607,8 0.7799 9.806 -35.6 0.4 572.6 29.00
2.0917 105.26 50.28 3468.2 0.1770 613.9 0.7891 9.792 -36.0 0.4 578.3 28.92
28,93 0.015
see text.
GeOz was used for runs 3 and 4 and a correction was made for the isolated residue. The hydrofluoric acid (15%) and hydrogen peroxide (5.00 and 2.36%) solutions were prepared from Baker Analyzed reagents. The hydrogen peroxide was diluted with demineralized water to which 2 p.p.m. of sodium stannate was added as stabilizer. The stability of hydrogen peroxide in presence of fluorogermanate ion was established by analyzing the product solutions from runs 2 and 4 on GeOz. These analyses were carried out by adding 15 g. of boric acid and then titrating with standard potassium permanganate solution.22 The millimoles of HzOzinitially added and the total millimoles found in the titrations were, in that order: 34.85 and 34.88 in run 2 and 34.66 and The Journal of Phgsical Chemistry
2.0310 103.34 50.30 3465.5 0.1731 599.9 0.7747 9.858 -35.7 0.4 564.6 29.07
34.68 in run 4. The possibility of catalyzed peroxide decomposition during solution of the germanium metaI was similarly tested. For the four runs, the millimoles found by titration compared to millimoles calculated to remain after stoichiometric reaction to oxidize the germanium were as follows: 34.7/34.9, 34.9/34.5, 35.4/35.0, and 35.3/35.3. Procedure. Polypropylene graduated cylinders were used to measure 100 ml. of the HF solution and 50 ml. of the HzOzsolution into the polyethylene bottles. The actual amounts were measured by weight. The germanium or germanium(1V) oxide was weighed into (22) I. M. Kolthoff and E. B. Sandell, “Textbook of Quantitative Inorganic Analysis,” Third Ed., Macmillan Co., New York, N. Y.,
1952,pp. 711, 712.
805
HEATOF FORMATION OF GERMANIUM DIOXIDE
a polyethylenc crucible which was loosely closed with a polyethylene stopper and placed on top of the loose cover over the small polyethylene bottle containing the HzOzsolution. Tables I1 and I11 record the essential data for the heat of solution measurements. The energy equivalents, &, of the initial systems were obtained by adding to the Eatd value (Table I) the heat capacity contributions of the Ge or GeOz, of the H F and HzOz solutions, and of the polyethylene and any water in excess of the standard amount placed in the calorimeter can. The data used for calculation of these increments to I s t d are listed in Table IV.
a tolerable approximation. The required heat of clilution data were taken (by graphical interpolation) from the K.B.S. tables.6
Results The following set of reactions is considered 2H202(aq) = 2H20(1)
Material
CP,
cal./g. deg.
Ref.
0,074 0.119 0.892 0,969 0.985 0.55
a
Ge GeOz(c, I) 1570 HF
5.00% HzQ2 2.36% HiOn Pol yethy lone
d d
solution
Ge(c)
y)lIzO
+ Odg)
=
+ yH2O
AH*’ [GeOz(c,I)]
Geode, I)
nHF.zHzO
-Qdiln
AHro[GeOz(c,I ) ]
+ QGeozcor- AH1 + 28.93 + 45.24
= -QGeGor
-206.37
=
=
- 132.20 kcal./mole
(I
For the GeOz runs a correction of 0.4 cal. was made for the energy of vaporization of water.23 The final temperatures fior all measurements on GeQzwere within 0.03’ of 25”, while for the Ge runs, they were 25.28, 25.19, 25.02, rind 25.01’. No corrections for these differences were made. In computing the mean value of Q,,,/mole for Ge02 (Table 111), the results of runs 3 and 4 were omitted since the corrections for the insoluble residues make these results inherently less accurate. The mean value, when included, is 0.04 kcal./mole higher, 80 that for most purposes it may be said that they provide a check on the resu11,s obtained with the completely soluble GeOz. It should also be noted that the approximation has been made that the heat of dilution of the H F solution by xHzOz.yH~O (z
