NOTES
2665
as plots of [(v/vo) - 11/47 vs. 4 j . The solid lines represent eq 1 with values of a from the OnsagerFuoss theory (Table 11) and values of b from the additivity rule (Table 111). The agreement between the calculated curves and the experimental points is satisfactory, at least up to I = 1.
Acknowledgment. The author expresses his indebtedness to Dr. E(. A. Kraus for his support, encouragement, and constructive criticism; his appreciation to Drs. J. S. Johnson, R. J. Raridon, and R. M. Rush for helpful discussion; and to Mr. J. Csurny for technical assistance. He also wishes to thank Professor H. L. Friedman of the State University of New York a t Stony Brook for his stimulating discussion and valuable suggestions.
Ion Exchange with a Two-Phase Glass
by R. H. Doremus General Electric Research and Deselopment Center, Schenectady, N e w York (Received November 27, 1967)
Many borosilicate glasses separate into two interconnected, amorphous phases. l p Z When the borate-rich phase is etched out, a porous glass of nearly pure silica (SiOJ results, which when heated collapses to a compact glass (Vycor) resembling fused silica. There is some evidence that commercial Pyrex glass, which is a sodium borosilicate glass containing more silica than the glasses from which Vycor is made, also separates into two continuous amorphous phases.2 However, no separation is observed in the electron microscope, nor can any phase be etched out from this glass, perhaps because the phase separation is on too fine a scale. In this work the exchange behavior of silver ions with Pyrex glass gives additional evidence that this glass contains two phases. Pieces of Pyrex glass (80% SiOz, 13% B203, 4.2% NazO, and 2% A1203, approximate composition in weight yo)tubing were placed in mixed sodium nitratesilver nitrate melts at 335" for several hours. Then layers of glass were etched off with 8% H F and were analyzed. Extrapolation of the profile of silver concentration to the glass surface gave the equilibrium concentration of silver that had exchanged with sodium ions in the glass. The exchange of silver ion in the melt with sodium ions in the glass can be represented by the equation Ag+(m)
+ Na+(g)
The exchange coefficient
=
Ag+(g)
+ Na+(m)
was calculated from the results. In eq 1, a is the thermodynamic activity of the nitrate in the melt, referred to a pure solution as the standard state as taken from the measurements of Laity,8 and C is the concentration of an ion in the glass. The measured K values for Pyrex glass are given in Table I. Table I : Exchange of Silver Ions in a Sodium Nitrate Melt with Pyrex Glass Mole fraction of ailver nitrate in melt
0.398
Exchange ooefficient, K
1.97 1.87 1.98 2.05 7 06 12.2
0 310 0.153 0.0475 0 I0022 3 x 10-6
If the solution of ions in the glass is ideal, K should be constant with concentration. This constancy has been found for silver exchange with sodium ions in soda lime glass (15% Na20) and in fused silica (3 atomic ppm of sodium both of which contain one homogeneous phase. Therefore, if the Pyrex glass were a single phase containing uniform sodium borosilicate groups, one would expect a constant K for this exchange, since the density of exchanging groups is even less than in the soda lime glass. Thus the change in K a t lower silver concentrations, shown in Table I, is evidence that the glass separates into two different phases. A two-phase glass can be treated as a mixture of two ideal phases, each with its appropriate exchange coefficient K1 or Kz,invariant with ionic concentration, as defined in eq l. In terms of the ionic concentrations in the two phases, numbered 1 and 2, the experimentally measured distribution coefficient K is
I n terms of the coefficients K1 and K2 this measured K is K =
- Kz) + K2(? + Ki) + K1 + Nl(K2 - K1)
yNi(K1 T
(3)
in which N1 is the mole fraction of exchangeable ions in phase 1 (a constant for any given glass composition) and T is u N ~ / u A ~ the , ratio of activities in the melt. Consistent values of the parameters in eq 3 for the data in Table I are KI = 2.3 X lo2,Kz = 1.6, and N1 = 0.047. This treatment of ion exchange with two phases is formally equivalent to that with a single phase contain(1) M. E. Nordberg, J. Am. Ceramic Soc., 27, 299 (1944). (2) R. J. Charles, ibid., 47, 559 (1964). (3) R. W. Laity, J . Am. Chem. Soc., 7 9 , 1849 (1957). (4) R. H. Doremus, unpublished results.
Volume 78, Number 7 July 1068
NOTES
2666 ing two different types of sites (polyfunctional exchanger). Cornaz and DeueP measured ion exchange with a bifunctional resin in water, and Barrer and Meiere presented results for bifunctional exchange in a zeolite, as well as equations similar to those given above. The borosilicate glasses used to make Vycor glass separate into a high silica phase and one containing soda, borate, and some silica.’n2 It seems likely that Pyrex glass also separates into silica and sodium borosilicate phases.2 The partitioning of sodium between the two phases in Pyrex, as calculated from the exchange results, suggests that phase 2 is the sodium borosilicate phase, since it contains 95% of the sodium, and that phase 1is the silica phase. ‘l’he coefficients K1 and K z are consistent with this assignment and give further information about the compositions of the phases. Silver is bound strongly to the SiO- or silicate group in a purely silicate lattice; for example, K = 120 (glass prefers silver) for silversodium exchange in a soda-lime glass.4 Thus the high K value found for the silica phase in this study implies that the anionic groups in this phase are SiO- groups, and that the boron concentration in it is low, Recent studies of surface adsorption on porous glass (a Vycor borosilicate from which the borate phase has been leached out) show that the boron remaining in the glass after leaching is concentrated at the internal surfaces of the Therefore there is little boron in the bulk of the silica phase, in agreement with the present deduction. The preference of the silica group for silver results from the high “field strength” (low effective anionic radius) of the group and the high polarizability of the silver ion. Groups with lower field strength, such as aluminosilicate and borosilicate, have lower affinity for silver ions compared to sodium. The value of Kz = 1.6 for silver exchange with the sodium borosilicate phase is close to this coefficient for silver-sodium exchange on the aluminosilicate groups in fused silica,4 in agreement with this prediction. The relations between the structure of anionic groups and their cation affinity are expounded in detail by Eisenman,gbased on both experiment and theory. The two-phase exchanger can be considered as a single nonideal phase, and the deviations caused by the presence of two phases absorbed in formal activities a ’ A g and for the ions in the glass. A constant exchange COefficient K‘ is then defined as
where the unprimed activities refer to the melt as before. From eq 3 and 4 and an integration of the relation between activities in the glass b(ln CAg
a’Ag>
acag
+
b(ln
a’NJ
CNa
The Journal of Physical Chemistry
bCNa
=o
the formal activities are found to be
and
Therefore from eq 4
and K’ = 1.8 for the parameters given above. This K’ can be used in equations for the membrane potential of a two-phase or bifunctional membrane. (5) J. P. Cornaz and H. Deuel, Helv. Chim. Acta, 39, 1220, 1227 (1956). (6) R. M. Barrer and W. M. Meier, Trans. Faraday SOC.,55, 1301 (1959). (7) M. L. Hair and I. D. Chapman, J . Am. Ceramic SOC., 49, 651 (1966). (8) M. J. D. Low and N. Ramasubramanian, J. Phys. Chem., 71, 3077 (1967). (9) G. Eisenman, Biophys. J., 2, 259 (1962); chapter in “Advances in Analytical Chemistry and Instrumentation,” Val. 4,C. N. Reilly, Ed., John Wiley and Sons, Inc., New York, N. Y., 1965, p 305.
The Nuclear Magnetic Resonance Spectrum
of Chloromethylphosphine by H. Goldwhite and D. G. Rowsell Department of Chemistry, California State College at Los Angeles, LOSAngeles, California 90058 (Received February 14, 1068)
Very few determinations of the signs of the coupling in trivalent phosphorus compounds constants JHCP have been made.1 Methods of sign determination involve either double resonance or the analysis of complex spectra. An initial investigation of the nmr spectrum of chloromethylphosphine showed that it was complex,2 suggesting that a complete analysis would give the sign of JHCP relative to JHP. Experimental Section The nmr spectra were obtained using a Varian A60 spectrometer fitted with a variable temperature probe. (1) G. Mavel, “Progress in Nuclear Magnetic Resonance Spectroscopy,” Val. 1, Pergamon Press, New York, N. Y., 1966, p 251. (2) B. Fontal, H. Goldwhite, and D. G. Rowsell, J . Org. Chem., 31, 2424 (1966).
