Feb., 1963
COXDUCTANCE
OF
ALKALISE:EARTH m-BESZENEDISULFOSATES IS WATER
of this work and Professor Fausto Ramirez of the State University of New York, Oyster Eay, N. Y.,
337
for stimulating discussions and suggestions during the course of this work.
ION ASSOCIATION IN POLY VALENT SYR4METRICAL ELECTROLYTES. V. THE CONDUCTASCE OF SOME A4LKALIKEEARTH m-BESZENEDISULFONATES IN WATER AT 25 O BY GORDON ATKINSOX AKD SERGIO PETRUCCI Department of Chemistry, Cniversity of iifaryland, College Park, Jfaryland Received August 1, 1966 The electrical conductances of Mg, Ca, Sr, and BaBDS have been measured in water a t 25". Analysis of the data by the Fuoss-Onsager equation shows all four salts to be essentially unassociated. The necessity of a term molar is pointed out. An alternative method of checkof (0)C3/z in the equation for concentrations > 2 X ing the A0 value and evaluating higher term contributions is proposed.
Recently the conductances of the C U + and ~ iLInf2 salts of m-benzenedisulfonic acid have been measured and the salts demonstrated to be essentially unassociated in water a t 25°.172 In this paper XIgBDS, CaBDS, SrBDS, and BaBDS are investigated in order to clarily further the phenomenon of unassociated 2-2 salts. I n addition, it was hoped to examine the effect of cation radius on association and further refine the Lo parameter for the BDS anion. The study also initiates an attempt to discover the contribution of terms of order greater than C in the Fuoss-Onsager equation. Experimental Materials.-The conductance water ( k = 0.5-1.0 X ohm.-' cm.-l.) was obtained by passing distilled water through two Barnstead Bantam mixed-bed ion exchange columns in series.3 The water flowing from the column \\-as filtered throdgh an ultrafine filter and collected in a Pyrex solvent flask after its conductance was checked by an in-line conductance bridge. The same collected sample was used both for preparing the stock solution of the salt and as the bulk solvent in the actual c0nduc.tance run. MgBDS was prepared from pure BaBDS'by standard ion-exchange techniques. After two recrystallizations from conductancewater, itwas dried for 4 daysover CaC12, giving the form MgBDS.HzO. Mg was determined by EDTA titration4 and the anion content WRS checked by converting a weighed amount of the salt to acid by ion exchange and titrating the acid with standard NaOH.1 CaBDS also was prepared from pure BaBDS by ionexchange techniques. After drying over CaC12 for 1week a t room temperature, i t had the formula CaBDS.l.5HzO. The Ca content was determined by direct EDTA titration using Eriochrome Black T as an indicator.& The anion was determined by the ionexchange technique. SrJ3DS was prepared by neutralization of crude HIBDSB with Sr(OH)2 in solution. The solution was decolorized with charcoal and the bulk of the HZSO, impurity removed as SrSOe. The SrBDS solution containing traces of SrS04 was concentrated by evaporation until turbid. It then was cooled and filtered to remove more SrSO4. This was repeated until no c.ould be detected in the filtrate. The SrBDS then wag crystallized twice from conductance water and dried a t room temperature over CaClz for 1 week. The dried salt is in the weighing form SrBDS.2Hz0. Sr was determined by the precipitation of SrSOl in 50% ethanol-water and the weighing of the dried anhydrous salt. The anion content was found b y ion exchange.
~-
(I) G. Atkinson, M. Yokoi, and C . J. Hallada, J . Ani. Chem. S O ~ .113, , I570 (1961). (2) C. J Hallada and G. Atkinson, ibid., 83, 3759 (1961). (3) Barnstead Bantam Model 0808, Barnstead Still and Sterilizer Co., Boston 31, Mass. (4) H. A. Flaschka, "EDTA Titrations," Pergamon Press, New Yoik, N. Y..1959, p. 75. ( 5 ) Reference 4,p. 77. ( 6 ) Matheson, Coleman and Bell, Norwood, Ohio, I t e m T 1164. (7) City Chemical Go., Now York, N. Y., Item 1762.
BaBDS was prepared as in ref. I. Ba was determined as BaFiOI and anion by ion exchange. The salt dries to a definite dihydrste over Cat212 a t room temperature. Equipment.-A Leeds and Xorthrup Jones bridge was used for the conductance measurements. The audio oscillator was a General Radio 1301A low-distortion oscillator and the null detection device was a General Radio 1232A tuned amplifier and null detector. The final null reading was made on a Heathkit 0-3 oscilloscope using the phase shift technique. With resistances ohm greater than 1000 ohms changes of resistance as small as could be detected. The resistance was measured a t 1000, 20100, 3000,5000, and 10,000C.P.S. and extrapolated to infinite frequency by an R vs. f-'/z plot. The thermostat was an 18-gallon transformer oil lmth insulated by 2 in. of styrafoam and stirred by a centrifugal pump. The temperature was controlled by a Sargtxnt "Thermonitor" using proportional control. The temperature was measured on a recently calibrated Beckmann thermometer and maintained t o 25.000 i 0.005°. The entire apparatus with the associated balances is enclosed in a constant temperature, constant humidity room that is completely shielded and furnished with a real ground. The cell used was the flask and was calibrated with extensively repurified KC1 using the standard KC1 conductance equation of Fuoss.8 The cell constant can be represented by h = 0.26331 - 0.5L, where L is the actual measured specific conductance of the solution. Method.-The technique used for a run has been described previously.l$2 Crrtain minor changes have been made t o improve the precision. All the solutions and the empty cell are weighed and corrected to vacuum. The weight buret is weighed on a Mettler H-15 balance and the cell on a 2-kg. solution balance using a glass tare of the same area. The stock solutions are analyzed directly for both anion and cation as a check on the stock preparation from weighed salt and solvent. Each run was repeated with a different solvent batch and stock solution. The average reproducibility between such runs was 0.05%.
Results Table I gives the equivalent conductances and concentrations for the four salts. In the work-up of the data no hydrolysis correction has been made for the CaBDS, SrBDS, and BaBDS. The MgBDS has been corrected using the method previously described' and a KI for Mg+2of 2.58.9 The hydrolysis correction for the Ca, Sr, and Ba salts is less than the experimental error of the work. The phoreograms of the four salts are exactly analogous to those observed for CuBDS aind MnBDS exhibiting the characteristic crossover behavior. The first analysis of the data was made by the simple Fuoss-Onsager equation 11 =
- &'C'/2 + E C l o g C + J C
(8) R. AI. Fuoss, et al., J . Am. Chem. Soc., 81, 1557 (1959). (9) D. I. Stock and C. W. Davies, Trans. Faraday Soc., 44, 856 (1948).
GORDOK ATKISSOSA N D SERGIO PETRUCCI
338
A' := Ao
+0.6 0.0
-0.6
Vel. 67
+ SC"z - EC log C
=
bo
+ JC
in the usual fashion, we note that the ii' us. C plot is only linear to C N 2 x 10-3 molar. Above this concentration the curve is concave downward. This is true both for the systems described here and for the ones described previously.lS2 Therefore, if the total concentration range is fitted with a single straight line, the line mill be a chord of the actual curve. This gives a larger Ao and a smaller J than a straight line taken through only the low concentration points. The rekults found by this approximate method are summarized in Table 11. This curvature in the ii' vs. C plot and the fact of the distorted Ao and J values are emphasized in Fig. 1. Here we have plotted the deviation function [A' (exp) - (Ao J C ) ] against C. The regularity exhibited by this phenomenon for different salts can be explained in a number of ways. One obvious explanation is the need for a small association constant for each salt. However this cannot be a total explanation since it does not explain the concentration dependence of the curvature. Another possibility is the necessity of a term
+
I
I
~~
TABLE I EQUIVALENT CONDUCTANCES AND COiYCEh.TR.4TIOEiSa'b Sa.11. = SrBDS Salt = MgBDS c x 104 A c x 104 1 4.2744 5,2042 7,0677 8,9341 9,1361 9.2140 18.116 24.350 33.263 41.921 51,564 59.416
102,990 101.960 100.270 98,806 98.761 98.642 93.883 91.606 89.128 87.172 85.380 84.097
Salt = CaBDS
cx
104
A
Io Run 2.6907
110.818
5,0210 7.9291 10,685
107.577 104.i82 102.740
12,428
101.641
11"Run 1,1307 2.3783
113.826 111.237
4,0846 5.5220 7,8867
108,724 107.036 104,887
111" Run 8.8671 15,307 26,908 36.165
104.062 100.228 95.760 93.316
49 796
90.606
T.4BLE 11 PRELIMINARY PARAMETERS
1 " Run 1,6967 3.9204 6.8620 9,8354 14.47'0 16,488 20.2Ei2 23,975
112,292 108.772 105,643 103.210 100.452 99.452 97.607 96.221
Salt
A0
J
aJ
MgBDS SrBDS CaBDS BaBDS
113 79 719.16 119 26 123 04
8001
4 4 4 4
8639 8620 8660
(0)C3/2in the conductance equation. is made attractive if one defines A' = A
(1.) 77 97 94 67
This possibility
+ xcl/z - EC log c = AO + J C + (0)c3/z
11" Run 4,88824 8,5328 15.902 21,698 30,818 37.058
107.576 104.258 99,682 97,189 93,972 92,318
Salt = BaBDS
cx
104
1
I o Run 1.3595 2.5728 4.1814 5.5686 7.6365
116.997 114.527 112.105 110.340 108.352
11" Run 5.3915
I O . 162 16.635 23,2613 31,808 38 563
110.607 106.410 102.459 99.494 96.439 9 1 602
Concentration units are molarities. Conduct,ancesare equivalent conductances. The number of figures reported for A is one greater than the probable errors would deem significant This is done 80 that other workers may recalculate the results without experiencing rounding-off errors. a
where the symbols a,re defined as before.1° If we define (10) R. M. Fuoss and F. Accascina, "Electrolytic Conductance," Academia Prom, New York, N. Y.,1960.
A plot of A" z's. C'/z is very close to linear for all four salts. Unfortunately a simple addition of the proposed JzC3'2 term does not seem adequate.ll We have ignored the very great possibility of a necessary viacosity correction. Since the correction could be of considerable size for such 2-2 salts we prefer not to estimate but shall wait until the actual viscosity measurements have been completed. Our present prejudice is that the minimum equation needed to represent such salts accurately would be A
=
A" - XC"z
+ EC log C + ( J - h ° F ) C + (Jz
+ SF)C"/"
where F is the Einstein viscosity coefficient. Therefore our final data analysis for Ao and J is confined to the concentration range where the A' plot is linear to within experimental error (approximately, C
