April 20, 1954
DIFFUSION COEFFICIENTS
AND CONDUCTANCES OF
2065
ELECTROLYTE SOLUTIONS
TABLE I OBSERVED A N D CALCULATED DIFFUSION COEFFICIENTS OF MAGNESIUM AND BARIUMCHLORIDES AT 25' BaCIx 106
MgClt
a, x 10'
C,
mole/l.
0.00000 ,00129 ,00163 ,00205 ,00270 ,00283 ,00309 .00361 .00100
Obsd.
... 1.187 1.180 1,168 1.16-1 l.lci7 1,157 1,155 1.164
Calcd.
(1.251) 1.180 1.176 1.163 1.161 1.160 1.153 1.152 1.159 Mean
3' x 106 (1.251) 1.258 1.255 1.256 1.254 1.248 1.217 1.248 1.256 1.253
conductances which according to Shedlovsky and Brown" are 1/2Ba++ = 63.64, 1/2Sr++ = 59.46, 1/2Ca++ = 59.50, 1/2Mg++ = 53.06. Thus, the limiting conductances of calcium and strontium ions are nearly identical, a situation which is inconsistent with the diffusion data. I t is hoped that experiments now being carried out in this Laboratory will clarify this situation. This investigation was supported in part by the (11) T. Shedlovsky and A. S. Brown. THISJOURNAL, 66, 1066 (1934).
[CONTRIBUTION FROM THE CHEMISTRY
Dx
C,
mole/l.
Obsd.
0.00000 .00068 .00097 .00109 .00139 .00214 .00229 ,00287 .00403 .00452 .00542
...
P' x
Calcd.
(1.337) 1.327 1.317 1.314 1.307 1.291 1.291 1.284 1,272 1.268 1.262 Mean
1.332 1.319 1.321 1.308 1.302 1.301 1.285 1.265 1.271 1.261
106
(1.387) 1.392 1.389 1.391 1.388 1.39A 1.397 1.383 1.382 1.390 1.386 1.390
TABLE I1 OBSERVEDALKALINEEARTHCHLORIDEDIFFUSIONCOEFFICIENTS IN DILUTESOLUTION Dx
r
c, mole/l.
106
MgClt
CaCIa
SrClr
BaCln
1.187 1.169
1.248 1.223
1.267 1.250
1.317 1.296
0.001 .002
Atomic Energy Commission under Contract A T (30-1)1375. NEW
HAVEN,CONXECTICUT
DEPARTMENT OF THE
UNIVERSITY O F WESTERN AUSTRALIA]
The Diffusion Coefficients and Conductances of Some Concentrated Electrolyte Solutions at 25' BY B. F. WISHAW'AND R. H. STOKES RECEIVED NOVEMBER 24, 1953 Diffusion coefficients of aqueous ammonium nitrate, lithium nitrate and ammonium sulfate solutions, and conductances of ammonium nitrate and ammonium chloride solutions are reported for high concentrations (0.1-8.0 moles/liter at 25"). Theoretical expressions for the diffusion coefficient and conductance of the 1:l electrolytes are found t o be remarkably successful. I n the case of ammonium nitrate there is evidence of marked ion-pair formation, the extent of which is estimated from the conductance data and then used in the interpretation of the diffusion results.
Introduction Diffusion data for aqueous solutions a t 25', to concentrations of several molar, have previously been obtained by the magnetically-stirred porous diaphragm cell method for eight alkali halides, hydrochloric acid and hydrobromic acid.2,3 The Goiiy diffusiometer has been used for similar studies on potassium ~ h l o r i d e ,ammonium ~ chloride and calcium ~ h l o r i d e . ~All these electrolytes are of the non-associated type, and while the interpretation of the diffusion data is by no means a simple task it is a t least not complicated by the effects of ionpair formation. There are, however, indications that such effects are present in the diffusion of bivalent metal sulfates, for which data a t low con(1) T h e work reported here is summarized from a thesis presented f o r the degree of Master of Science of the University of Western Australia by B. F. Wishaw i n July, 1953. (2) R. H. Stokes, THIS J O U R N A L , 72, 2243 (1950). (3) P.J. Dunlop and R. H. Stokes, ibid., 73,5456 (1951). (4) L.J. Gosting, i b i d . , 72,4118 (1950). (5) J. R. Hall, B. F. Wishaw and R. H. Stokes, ibid., 7 6 , 1.556
(1953).
centrations (< 0.01 M ) are available from the conductometric diffusion cell studies of Harncd and collaborators.e~7 In the present paper we report diffusion measurements on concentrated solutions of ammonium nitrate, lithium nitrate and ammonium sulfate by the Goiiy method, in order to provide further basis for studying the effects of ion-pair formation. These measurements are supplemented by some conductance determinations.
Experimental Materials.-Ammonium nitrate of analytical reagent quality was recrystallized and made into a concentrated stock solution, the composition of which was found by careful density measurements (reproducible to a t least 1 part in 30,000) with the help of recorded density data.8vg Ammonium chloride of analytical reagent quality was used (6) H . S. Harned and R. M. Hudson, ibid., 7S, 5880 (1951). (7) H.S. Harned a n d C. A. Blake, ibid., 73,4255 (1951). (8) "International Critical Tables," Val. 111, McGraw-Hill Book Co., Inc., New York, N. Y., 1929. p. 59. (9) L. H. Adams and R. E. Gibson, THIS J O U R N A L , 64, 4520
(1932).
without further purification, in the form of a concentrated stock solution analyzed gravimetrically for chloride as silver chloride. Lithium nitrate: Reagent grade lithium hydroxide was precipitated as carbonate by saturating with carbon dioxide. The washed and dried carbonate was then dissolved in a known w i g h t of previously analyzed nitric acid until the acid was just ncutralized. After boiling out carbon dioxide, the solution mas made up to a known weight and its concentration was calculated from that of the nitric acid. The pH of the stock solution was close to 7.0. A mmoflizim szdfate of analytical reagent quality was made into a stock solution which was analyzed by density and by grxvimetric determination of sulfate as barium sulfate. In each case more dilute solutions were prepared as required by weighing out suitable amounts of stock solution a n d making up to known volumes a t 25" in calibrated stand:ird flasks. Doubly distilled water with a specific contluctivity of 2 X 10-6 ohm-' c m . - I was used throughout. Diffusion Measurements.-These were made with the Goiiy diffusiometer previously d ~ s c r i b e d . ~The expcrin i c ~ i t : i l results are given in T:tl,li%I :111(1 t l i o v for t h e 1 : 1 rl(~(,trolytes :ire plottc.tl i n Fig. 2.
-
capable of 0.1% accuracy; this estimate is confirmed by the excellent agreement of our data for ammonium nitrate with those of Campbell and Kartzmark,'o and of our result for 0.1 N ammonium chloride with that of Longsworth." This accuracy is quite sufficient for the concentrated solutions studied here. The conductance cell was of a simple tubular design with electrodes 1 cm. square separated by about 25 cm., and was calibrated with potassium chloride solutions at 25' using the Jones and BradshawX2standards. The observed conductivities are given in Table 11. Table 111 presents the diffusion and Conductance data interpolated t o round molarities. Our values for the conductance of ammonium nitrate solutions agree with those of Campbell and Kartzmarklo within 0.1 yo over the entire concentratiot~ range studied; and our value for 0.1 rZI ammonium chloride (.\ 128.8) agrees closely with Longsworth's value" a t this concentration, the highest which he studied ( A 128.75).
TABLE I1 CONDUC1.ANCES O F AQUEOUS AMMONIIJIr S 2;" NII'RAI'R A S I ) ~ H l . l ~ R I T )~EO l . 1 7 ~ l 1 0 NA'l' 4" so3 NIIiCl
T?QITlVAI.ENI.
TABLE I
NHiNOj C5
n n5o;
Ac, b
D X
7.628
0.0610 .lo13 ,2013 ,203; ,1927 ,2513 .1920 .1897 .lo20 .I990 .1813
1.791, 1,709 1.750, 1.731, 1.695, 1,638, 1.576 1.522, 1.469, 1 418, 1 338
0.0710 .I279 ,2681 . ,5989 1.014 1 .
