EQUIVALENT CONDUCTANCES
1499
OF BARIUM ALWNESULWNATEB
T H E LIMITING EQUIVALENT CONDUCTANCES OF AQUEOUS SOLUTIONS OF SOME BARIUM ALKANESULFONATES' L. R. DAWSON, M. GOLBEN, G. R. LEADER, AND H. K. ZIMMERMAN, JE. Department of Chemirtry, University o j Kentucky, Lextngton, Kentucky Received September 81,1860
In connection with work being performed in this laboratory on the use of dkanesulfonatea as solutes in electrolytic solutions, it became desirable to know the relative mobility of some of these ions, particularly the methane- and ethanesulfonates. The only previously published information concerning these ions which was found is that given by Berthoud (l), who reports a limiting ionic conductance of 66 for methanesullonate ions and of 60 for ethanesulfonate ions at 25'C. However, his measurements were made on the wids and do not appear to be of high precision. Moreover, his values are b d on an assumed value of 340 for the limiting equivalent conductance of the hydrogen ion, whereas the best presentday value (3) is 349.8 at 25°C. Therefore, it seemed advisable to repeat the measurements and to extend them. The results of that work are reported here. EXPERIMENTAL
Materials Methane- and ethanesulfonic acids supplied by the Indoil Chemical Company were used. The manufacturer stated that the concentrations of these were 95 per cent and that they contained approximately 1 per cent sulfuric acid. Analytical-grade barium hydroxide was used to prepare a nearly saturated solution, which was filtered to remove carbonate and then standardized. Solutions of barium methanesulfonate and barium ethanesulfonate were prepared and the concentration of each was determined by two methods: (I) An aqueous solution of the acid was neutralized to a pH of 7 with the standardized barium hydroxide solution. The neutralized solution was digested and then filtered to remove precipitated barium sulfate; the filtrate and washings were made up to a known volume. From the total acid present, the amount of sulfuric acid (determined gravimetrically by igniting the precipitate on ashleas filter paper and weighing) was subtracted to give the concentration of barium alkanesulfonate in the solution. (9)Measured portions of the barium alkanesulfonate solutions were treated with sulfuric acid. From the weight of barium sulfate obtained, the concentrations of the solutions were calculated. Normalities of the stock solutions determined by these two methods were in agreement to the extent shown below: B A P I M SALT
I B~(CHISO~)L Ba(CIHbSOdL
j
N
1
Y
~
0 3540 0 3086
0 3517 0 3051
1 This paper is based upon research performed under Contract No. W36-039-sc 38184 for the U. S. Army Signal Corps.
1500
DAWSON, QOLBEN, LEADER, AND ZIMMERMAN
Propanesulfonic acid was prepared from n-propyl mercaptan (Eastman Kodak Company) by oxidation with nitric acid as described by Vivian and Reid (6). When the reaction was complete, the excess nitric acid was evaporated, and the midue of propanesulfonic acid was diluted with water and neutralized with C.P. barium carbonate. The barium salt w a ~isolated by evaporation after removing excess barium carbonate and was then purified by two recrystallizations from hot water and dried. Analysis of the salt by precipitation of barium sulfate from a weighed sample showed 101 per cent purity, indicating the presence of about 3 per cent barium nitrate, which was the most likely impurity. All solutions were prepared with water which was purified by successive distillations in Pyrex apparatus from dichromate solution, and then from an alkaline solution of potassium hydroxide and barium hydroxide. Its specific conducohm.-' tance was about 2 X Apparatus and procedure
Conductance measurements were made with a Leeds & Northrup conductivity bridge of the Jones-Dike type. A weighed quantity of conductivity water was placed in the cell (Washburn type, cell constant 0.01267), which waa joined to a mixing bulb. The standard solutions were added in portions from a microburet; after thorough mixing following each addition, the conductances of the resulting solutions were determined. The volume added each time w a noted to permit calculation of the salt concentration a t each point. The temperature of the cell was held constant to &O.Ol"C. by means of a thermostatically controlled bath (containing ice for work a t 0°C. and kerosene for work at higher temperatures) constructed with a 1-gal. Dewar flask. RESULTS
The equivalent conductances observed a t 0", 20", and 25°C. for the methaneand ethanesulfonates of barium are shown in figures 1 and 2 and are representative of the curves obtained in all cases. Additional runs were made on these two salts at 25°C. also; those data are presented in table 1, together with the data for barium propanesulfonate at 25°C. Extrapolation of the data to determine A. was performed by the method of least squares in each case. A summary of the values obtained is presented in table 2. The following values for the limiting equivalent conductance of the barium ion are given in the literature:
I00 80
h 80 40
20
MI
a02
OD3
0.04
n
fi
FIG. 1
FIG. 2
FIQ. 1. The equivalent conductance of barium methanesulfonate in water a t Oo, a', and 25°C. uersw the square root of the concentration. FIG. 2. The equivalent conductance of barium ethanesulfonate in water a t ,'O 20", and 25" C. uersua the square root of the concentration. TABLE 1 Equivalent conductivities of solutions of the barium alkanesuljonates at db°C.
N X
N X I@
394.3 752.3 946.9 1134.9 1303.1
0.0119 0.0274 0.0308 0.0337 0.0361
0.0196 0.0239 0.0272 0.0305
737.9, 928.9
109.0 107.4 106.2 105.7 105.2
JC
1118.3 1498.3 1873.3
357.7 460.0 561.4 717.5 921.9 973.9
100.4 99.96 99.53 98.76
1 1 0.0334 0.0387 0.0433
98.35 97.17 96.66
0.0189 0.0214 0.0237
97.99 97.63 97.54 96.84 %.34 96.46
0.0268 0.0304
0.0312
TABLE 2 Limiting equivalent conductances of the barium alkanesuljonates ShLT
T
A-
A0
'C.
Ba(CsH&O&
. , . . ., . . . . . . . . . . . . . . . . . .
0.0 20.0 25.0 25.0
57.7 99.5 112.4 112.6
24.1 42.5 48.8 49.0
0.0 20.0
52.9 91.7
25.0
103.2
25.0
103.7
19.3 34.7 39.6 40.1
25.0
100.7
37.1 (corrected, 36.1')
-
* As mentioned previously, analysis of the barium propanesulfonate indicated the presence of about 3 moles of barium nitrate t o each 100 moles of sulfonate. Since the limiting equivalent conductance of the nitrate ion is 71.4 at 25'C. (2), the presence of this much nitrate would cause the observed value for the propanesulfonste t o be high by 2.7 per cent. The corrected value is obtained by lowering the observed value by thia amount. 1501
1502
DAWSON, CIOLBEN, LEADER, AND ZIMMERMAN
From the temperature coefficient of conductance of the barium ion given in the International Critical Tables (4), the limiting equivalent conductance a t 20'C. can be calculated to be 57.0. Using these values for the barium ion, the limiting equivalent conductances of the alkanesulfonate ions are found to have the values shown in the last column of table 2. A plot (not included) of equivalent conductance versus temperature for the methane- and ethanesulfonate ions yields curves which are almost straight lines and which come closer together as the temperature is lowered. The conductance a t 0°C. is greater in both caaes than would be predicted from the Walden's rule value obtained by use of the data a t 20°C. and 25"C., as shown by the following calculation. T "C.
0.0 20.0 25.0
I
AN FOP
Ba(CH6Oh
1.033 1.ooO 1.004
I
Ba(C:HdOs)r
0.948 0,922 0.922
Comparison of the limiting conductances of the alkanesulfonate ions with those reported (2) for the ionic conductances of fatty acid ions a t 25°C. shows that there is a difference of 5.1 between the values for acetate and propionate ions as compared with a difference of about 9.2 resulting from an analogous introduction of a methylene group in the alkanesulfonate series. For the second methylene group, the differences are 3.2 and 3.5 to 4.0, respectively. This indicates that for short alkyl chains the influence of chain length on the conductance is significantly greater for the more soluble sulfonates than for the fatty acid ions, and further shows that the effects probably become very much akke as the alkyl chain is extended beyond a length of about three carbon atoms. SUMMARY
Limiting equivalent conductances of the methane-, ethane-, and propanesulfonates of barium in aqueous solutions have been determined. The data have been used to calculate the ionic conductances of the anions and to test Walden's rule. The effect of the introduction of a methylene group into the alkane moiety on the conductance in the sulfonate series has been compared with the effect of a similar change in the fatty acid series. REFERENCES (1) BERTHOUD, A,: Helv. Chim. Acta la, 859 (1929). (2) GLASSTONE, S.: Introduction to Electrochemistry, pp. 56-7. D. Van Nostrand Company, Inc., New York (1947). (3) HARNED, H . S., AND OWEN,B. B.. Physical Chemistry of Electrolytic Soluliona, p. 172. Reinhold Publishing Corporation, New York (1943). (4) International Critical Tableu, 1st edition, Vol. VI, p. 230. McGraw-Hill Book Company, Inc., New York (1929). (5) Landolt-BBrstein-Roth Tobellen, 5th edition, 3rd supplement, Vol. 3, p 2053. Julius Springer, Berlin (1938). (6) VIVIAN, D. L . , AND REID,E. E.: J. Am. Chem. SOC.67,2559 (1935).
