Aug. 20, 1958
DIELECTRIC CONSTANTSOF ALKALINE EARTH SALTS I N N-METHYLACETAMIDE 4233 [CONTRIBUTION FROM
THE
DEPARTMENT OF CHENISTRY, UNIVERSITY OF
&NTUCKY
]
Solvents Having High Dielectric Constants. IX. Conductimetric Behavior of Some Alkaline Earth Salts in N-Methylacetamide at 40°1b2 B Y LYLER.
D.%WSON,
GEORGER. LESTERAND PAUL G.
SEARS3
RECEIVED JANUARY 31, 1958 The equivalent conductance of each of twenty alkaline earth salts in N-methylacetamide (NMA) has been determined a t several concentrations in the range 1-280 X lo-' N . The resulting phoreograms are very slightly anabatic for all salts except barium and strontium nitrates. Excellent agreement exists between the observed results f n d those predicted theoretically by the Onsager equation. Values of ADhave been determined from Shedlovsky plots of A 0 versus C. The behavior of corresponding anhydrous and hydrated salts appears to be identical within experimental error. The limiting ionic equivalent conductances of the alkaline earth ions in NMA have been calculated by differences utilizing previous results based on the octadecyltrimethylammonium octadecyl sulfate method. The barium ion unexpectedly is slightly less conducting than the calcium and strontium ions in NMA.
Introduction Preceding papers from this Laboratory4-6 describe the conductance behavior of more than fifty uni-univalent electrolytes in N X h , an unusual solvent characterized a t 40" by an exceptionally high dielectric constant (165.5 a t 10 megacycles), moderate viscosity (3.02 centipoise), and extensive dissolving and dissociating power. Excellent agreement between the experimental results and those predicted theoretically by the Onsager equation' indicates that all of the ionophores and also ionogens such as hydrogen chloride and 2,4,6-trinitrophenol are dissociated completely in dilute NMA solutions. The availability of values for limiting ionic equivalent conductances6 also permits an extension of theoretical analyses to conductance data for unsymmetrical multivalent electrolytes in NMA. The objectives of the research described herein were to study the conductances of several alkaline earth salts in dilute NMA solutions, to compare the behavior of corresponding anhydrous and hydrated salts and to extend generally the existing knowledge concerning the potentialities of NMA as an important electrolytic solvent. Experimental Apparatus and Procedure.-These have been described in detail p r e v i o ~ s l y . ~ , ~ Salts.-Reagent grade salts which were purchased from the Mallinckrodt Chemical Company and the G. Frederick Smith Chemical Company were used without further purification. The non-hydrated salts were dried to constant weight in a vacuum oven a t an appropriate temperature. -411 of the salts were analyzed for water content by the Karl Fischer method using Fisher stabilized single-solution Karl Fischer reagent after it had been standardized against sodium acetate ti.ihydrate.S Allso, all the halides were analyzed by the Fajans methodg and were found to be very pure. (1) This research was supported in part by a grant (NSF-GZ748)
from the National Science Foundation. (2) Taken from a dissertation submitted by George R. Lester in partial fulfillment of the requirements for the degree of Doctor of Philosophy. (3) Research Department, Inorganic Chemicals Division, hlonsanto Chemical Company, St. Louis 24, Missouri. (4) L. R. Dawson, P. G . Sears and R. H. Graves, THISJOURNAL, 77, 1986 (1955). ( 5 ) L. R. Dawson, E. D. Wilhoit and P. G. Sears, i b i d . . 78, 1569 (1956). ( 6 ) L. R. Dawson, E. D. Wilhoit, R. R. Holmes and P. G. Sears, ibid., 79, 3004 (1957). (7) L. Onsager, Physik. Z., 26, 277 (19271 (8) G. G. Warren, Can. Chem. Process Inds., 29, 370 (1945). ( Y ) I. >I. Kolthoff and E. B. Sandell, "Textbook of Quantitative Inorganic Analyqis," The Macmillan Co.. New York, S . Y.,1952, p.
543.
The molecular weights of the hydrated solutes were adjusted in necessary cases to conform with the analytical data. For convenience, each hydrate is listed in the following tables as the one containing the nearest integral number of associated water molecules. Solvent .-The preparation and purification of NMA has been described p r e v i o ~ s l y . ~The , ~ solvent which was used in this study had a freezing point of 30" and the following physical properties a t 40": conductivity, 1-5 X ohm-' cm.-l; density, 0.9421 g./ml.; dielectric constant, 165.5; viscosity, 0.0302 poise.
Results The very extensive tabulation of corresponding values of the equivalent conductance and the equivalent concentration for each of the twenty electrolytes is omitted herein to conserve valuable space but is available elsewhere.lo However, the more useful results which were derived from these data are conveniently summarized in Tables I and 11. TABLEI TESTOF ONSAGER'SEQUATION FOR SOLUTIONS OF SOME ALKALINE EARTHSALTS IX N-METHYLACETAMIDE AT 40' Salt
BaC12 BaC12.2H~0 BaBr2 BaBrn.2H20 BaI2 BaI2.2H20 Ba( XOs)a Ba(C10J2 Ba(C1O4)2.3H20 SrC12.6H~0 SrBr2,HzO SrBr2.6H20 Sr(SOJ2 Sr(C1Oa)2.3H20 Sr(C104)2 CaBrs 4H10 Ca(C104)24H20 Ca(NOa)2.4H20 MgClz.6HzO Mg(N0s)2 5H?O
Exptl. slope An
(SE)
21.61 21.61 22.90 22.90 24.58 24.65 24.64 27.05 27.05 21.93 23.13 23.13 24.95 27.25 27.26 23.12 27.00 24.66 21.28 24.20
22.9 22.9 23.5 23.5 22.1 22.1 28.0 24.3 24.4 23.9 23.9 23.9 29.3 24.1 24.0 23.6 24.9 24.9 23.3 25.8
25.3 25.3 25.5 25.5 25.7 25.7 25.7 26.0 26.0 25.4 25.5 25.5 25.8 26.0 26.0 25.5 26.0 25.5 25.3
25.0
- 10 - 10 - 8
- 8
- 14 - 14 9 - 7 - 6 - 6 - 6 - 6
-
12
-
- 8 - 8
- 4 - 3 - 8 1
(10) A complete tabulation of corresponding equivalent conductance and concentration data has been deposited as Document number 5524 with the AD1 Auxiliary Publications Project, Photoduplication Service, Library of Congress, Washington 25, D. C. A copy may be secured by citing the Document number and by remitting $1.25 for photoprints, or $1.25 for 35 mm. microfilm in advance by check or money order payable to: Chief, Photoduplication Service, Library of Congress.
L. I
