VISCOSITIES, ELECTRICAL COiYDUCTIS?TIES, AND SPECIFIC VOLCMES O F ACETIC ACID-STANNIC CHLORIDE SOLUTIONS BY J. D. STRANATHAN AND JOHN STRONG
The dependence of viscosities of solutions upon the concentration of the solution components is most logically considered under four heads:- ( I ) Those for which the viscosity of the solution is the same as that calculated from a weighted mean of the viscosities of the components, that is, from the additive law; ( 2 ) Those for which the viscosity at any concentration is greater than that calculated from the additive law; 13) Those for which the viscosity at any concentration is less than that calculated from the additive law; (4) Those for which the viscosity a t some concentrations is greater and at other concentrations less than that given by the additive law. For solutions of the first type there is no change in volume upon mixing; that is, the specific volume of the mixture is a weighted mean of the specific volumes of the two components. Also, the mixing is accompanied by neither evolution nor absorption of heat. For solutions of the second type there is a contraction upon mixing and an evolution of heat. For mixtures of the third type there is an expansion upon mixing and an absorption of heat. The expansion or contraction is usually interpreted as a decrease or an increase in association.’ The acetic acid-stannic chloride solutions studied by the authors are examples of type two solutions. Their viscosities are often hundreds of times larger than those calculated from the additive law, there is marked evolution of heat upon mixing, and the volume contraction for some concentrations is as much as 32.10% of the volume calculated from the additive law. In fact S O lutions of acetic acid and stannic chloride are quite abnormal in that their physical properties deviate from the weighted mean by a far greater percentage than is the case for any other similar solution known to the authors. Preparataon of Solutions:-Anhydrous Stannic Chloride and 99.7% Glacial Acetic Acid were used to make the solutions. Some indication of purity is given by the fact that the specific electrical conductivity of the acetic acid was of the order of 4 X IO-*, while that of the stannic chloride was of the order of 2 X IO-^ reciprocal ohms. Twelve mixtures varying in mol fraction concentration of SnC14 from 0.0244 to 0.41 I I were prepared in wide mouth, glass stoppered bottles. At concentrations slightly higher than 0.41 I I the mixture breaks into two liquid layers, the lower one of which is nearly pure SnC14. Great care was necessary in making up the solutions to avoid unnecessary impurities. SnC14and solutions rather rich in it fume vigorously when exposed to moist air. Likewise, acetic acid takes up water rather readily. To avoid these difficulties, the weighted bottle into which the solution was to be put was filled with dry air. The stannic chloride was siphoned in through a glass Bingham: “Fluidity and Plasticity,” 160 (1922).
1421
.4CETIC ACID-STANNIC CHLORIDE SOLUTIONS
tube extending into the bottle through a tight-fitting stopper. Only dry air was let into the container from which the stannic chloride was siphoned. After weighing the bottle and stannic chloride, acetic acid was let in in the same manner. I n this way all fuming was avoided. T'tscostty Measurements :-The design of apparatus for viscosity measurements of acetic acid-stannic chloride solutions must take into account the following items:-( I ) The viscosities to be measured vary widely, depending upon concentration; at a temperature of 2 5 . 2 T . they vary by a factor over 300. The apparatus must be adaptable to such widely varying viscosities. [ 2 ) SnClr solutions fume vigorously when changing the composition of the solution, this fuming results in the formation of stannic oxide which would clog the capillary of the viscometer. The measurements must therefore be carried out with
i
TO CONSTANT
VACUUM
y,
lowed to flow into, rather than out of, a CAP/LLAR~ vessel of known volume. __ - _ _ The apparatus which seemed best adapted to the needs is indicated in Fig. - __ I . The bottle containing the solution FIG. I was nearly submerged in a water bath 0 . 0 ; C" by a thermost,at. The soheld at a constant temperature of 2 5 . 2 ~t lution was forced upward through the capillary into a graduated burette by creating a constant, partial vacuum in the burette. The difference between the pressures on the surfaces of the liquid in the bottle and in the burette was read directly from a water manometer. The apparatus was adapted to the measurement of widely different viscosities in that capillaries of different diameters could be used; also, the difference of pressure forcing the liquid through the capillary could be varied. Five different capillaries were used, their diameters varying from 0 . 2 8 4 nim. to 2.474 mm. The largest of these was used only for measurements at zero degrees. Each capillary was slightly under 8 cm. long and was cut off square at the ends. Data were taken as follows. A difference of pressure was applied by creating a constant, partial vacuum in t,he graduated burette. The times were recorded from a stop-watch whenever the liquids rising in the burette passed a
1422
J. D. STRANATHAN AND J O H S STRONG
graduation indicating a cubic centimeter. From these d a t a the times required for each cc. to flow through the capillary were obtained. These time intervals increased as inoreand more liquid flowed into the burette, due to the back pressure exerted by the rising column. The resiprocal of the rate of flow(At Av) was thenplottedagainst thenumberofcc. whichhad flowed into the burette since starting to count time, each value of A t / A v being plotted in the middle of the volume interval to whichit corresponds. An example of the resulting curve is shown in Fig. 2 . As the liquid flowed back through the capillary in to the containing bottle, heightsof theliquid in the bottleandinthe burretten.ererecordedat variousintervalsalongtheburette
WLUME-cc PIG. 2
scale. From the difference of height, the density of the liquid and the pressure occasioned by the partial vacuum in the burette, the actual pressure forcing the liquid through the capillary was calculated at various intervals along the burette. These pressures were likewise plotted against the volume of liquid in the burette. The curve is shown in Fig. 2 . The Poiseuille equation relating the absolute viscosity q of a liquid of density rl to the rate at which it flows through a capillary of radius i- and length I under the influence of a pressure p grams per sq. cm., is =
*( + 8(1
X)
A t ) - ___ d 5 8T(l X)
+ (2) Av
where h is the Couette correction for the effective length of the capillary and where the second term is the correction due to the kinetic energy of the liquid streaming through the capillary. If the kinetic energy correction be small it
I423
-4CETIC ACID-STASSIC CHLORIDE SOLUTIOSS
At . is apparent that the product p - IS proportional t o viscosity, and therefore Av
constant irrespective of what pressure is used t o force the liquid through the capillary. That is, the products of the ordinates of the two curves shown in Fig. 2 should be constant. The products calculated a t regular intervals from the experimental curves shown are tabulated across the top of Fig. 2 . Their constancy is an indication of the accuracy of the work. The average variation At from the mean in this case is 0 . 2 7 5 . The average value of p - obtained from AY
experimental curves was used in the calculation of viscosity. The correction X to add to the measured length of the capillary is given' by 1.64times the radius of the capillary, in case the ends are cut off square. for the largest Correction was made for this, though it amounted to only 1.37~ capillary, and much less for all others. Likewise, correction was applied for the kinetic energy of the liquid issuing froni the capillary. Rarely did this correction exceed a few tenths of IC;, though for one or two of the weaker The corrected solutions (weaker in SnC14) it did amount to a little over 17. absolute viscosities found for solutions of stannic chloride in acetic acid are shown in the second column of Table I. The data is for a temperature of 2 5 . 2 =+ 0.05 C". By way of checking the reliability of our neth hod, a determination of the viscositj- of water a t 2 5 . 2 ' C. was made. The average of two determina-
TABLE I Mol Fraction Concentration of Sn Cl:
Absolute Viscosity
. 0000
0.011j j
,0244
,02121
,0520
,04373 ,189; 963 2 , j82 3.034 2,909
. I084 ,1719 ,2290 . 2 j Z j
,2682 '2969 .3Ijl '3498 ,3608 .41I I I . 0000
2.105
1
649 ,844 ,691 ,4234 .0084* '
Specific Volume
0.9486 ,8841 ,8096 . 7 10; '6330 . 5830 .56jj
11.85
x
20.74
8.68 3.6jo*"
2.887 2 . jro
,5446 ,5361
2 . 591
,5206
2.8j8 3.478 3.967
.5'j2
4.550
. j 2 jo
'4436
10-4
2j.29
,5580
"Dictionary of .ipplied Physics," 1, 1047. *Rather poor result, due t o tendency for capillary to clog. **There is reason to believe t h a t this value is low.
1
Spwific Elert r i c d ConductivitJ
1424
J. D. STRANATHAN A S D JOHS STRONG
tions was 0.00886. This compares very favorably with the value 0.00889 interpolated from values given for different temperatures in the Smithsonian j j for pure acetic acid compares someTables. Likewise, our value of 0.011 what less favorably with the value 0.01121 interpolated from data given in the Smithsonian Tables, or with the value 0 . 01194 given by Gross.' The curve of Fig. 3 shows the observed manner of variation of viscosity with concentration. Since the viscosities of both components are negligibly small as compared to the viscosity of the solution at all except very small con -
FIG.3
centrations, it follows that this curve also represents practically the deviation of the viscosity from the valuc calcu1:zted from the weighted mean of the viscosities of the two components. The rnagnituclt of the deviation from the value calculated from the additive law is unusually large. The peak value of the curve is larger than the value calculated by the additive law by a factor of 2 8 2 . The viscosity represented by the peak is greater than that of the most viscous component by a factor of 263, using our value for the viscosity of acetic acid. This factor of increase is much greater than that for any other non-colloidal solution known to the authors. The most marked of any systems found in the literature for a temperature around 25°C are those of aniline-acetic acid and o-chlorophenol-quinoline. Certain concentrations of aniline-acetic acid solutions* have viscosities 6.1 times t h a t of t h e most viscous component; certain concentrations of o-chloroPau! 11.Gross: Dissertation, Columbia University (19191 *Thole, Mussell, and Dunstan: J. Chem. Sac., 103, I I 14 (1913)
ACETIC ACID-STAKNIC CHLORIDE SOLUTIONS
1425
phenol-quinoline solutions' show approximately t h e same ratio. At solutions have viscosities 2 8 o°C certain o-chlorophenol-quinoline times t h a t of t h e most viscous component. Viscosity diagrams for which one of the components is SnClr have been obtained by K.S. Kurnakov, S. I. Perlmetter, and F. P. Kanov,* and by N. S. Kurnakov and N. N. B e k e t ~ v . ~ These diagrams show maxima. The curves were available to the authors, however, and therefore no information regarding the magnitude of the maxima is a t hand.
FIG.4
The position of the maximum viscosity, which is here indistinguishable from the position of the maximum deviation from the weighted mean of the component viscosities, is accurately a t a concentration 0.25. This concentration is precisely that which would be given by a compound SnCI4.3CH3 COOH. In view of the extremely large deviation from the additive law, the accuracy with which the peak falls a t the concentration corresponding to this compound, and the unusually great volume contraction and heat evolution upon mixing, it seems logical to attribute the marked change in properties with roncentration to the formation of a compound SnC1,.3 CH3COOH. An attempt to determine the fusion curve was made to see whether it gave any indication of a compound. Supercooling and the fact that the viscosities increased gradually until the samples became amorphous solids precluded the possibility of such determinations. ' A Bramle J. Chem. Sac. 109, 4 i 1 (1916). 2 ,J. Russ. ?hys. Chem. SOC.,48, I658 (1916). 3 J. Russ. Phys. Chem. Soc., 48, 1694 (1916).
1426
J. D. STRASATHAS A S D JOHN STRONG
In order to see whether the position of the maximum of the viscosity curve, and thence the position of the maximum deviation from the weighted mean of the component viscosities, shift's with temperature, some measurements of less precise nature were carried out a t oo C. The bottle containing the solution was placed in a mixture of ice and water. After allowing considerable time for the temperature to fall to oo C., the viscosity was measured. The results are plotted in Fig. 4. It is apparent that the maximum viscosity increased by a factor of about 23 for a drop in temperature of approximately 2 5'. This corresponds to an extremely large temperature coefficient. The position of the maximum of this curve is rather doubtful. Remembering that it is characteristic of most viscosity curves to be unsymmetrical about the maximum' (and the solutions here studied show some dissymmetry at z5.zo), it seems probable that the maximum of this curve is very close t o a concentration of.o.2j. If the position of the act,ual maximum is shifted toward higher concentration at o o , the shift is certainly very small; it is considerably less than 0.01 in concentration even though the viscosity is increased by a factor of 23. I n view of the tremendous temperature coefficient of viscosity and the difficulty in getting the very viscous solutions to cool uniformly to oo, it appears probable to the authors that there is no actual shift in the position of the maximum with temperature changes. Contraction o j Solutions upor2 JIz'xing :-The densities of the solutions were measured a t 2 5 . 2 ' C. with a sensitive Joly Balance. From the absolute specific volumes (Table I), the per cent contraction of solutions upon mixing were calculated and tabulated in Table 11. The maximum percentage contraction of 32.10 is unusually large. The position of this maximum is approximately at a mol fraction concentration of 0.31. The fact that this maximum does not occur at identically the same concentration as does the maximum viscosity deviation is contrary to the view presentedbyDenison* that the maximum deviations in the various property curves should occur at the same concent,ration. AIany other solutions show this same disagreement, however; among them are Aniline-Acetic Acid and o-Chlorophenol-.~niline.3
TABLE I1 Mol Fraction Concentration
Perrent Contraction
. 0000
. 00
,0244
5.57
,0520
12.22
,1084 "719 ,2290 ,2527
20.50
26.55 30.01 31.12
Mol Fraction Concentration
,2682 ,2969 ,3151 ,3498 ,3608 .41I I
Percent Contraction
31.38 31,81 32. I O 31.99 32.07* 30.48
*When t h e observed specific volumes are plotted against concentration, it is apparent t h a t the value for this concentration is slightly low. Using the specific volume taken from t h e smooth curve. the Dercent contraction is 2 1 . 8 2 inatead of w . o i . See, for example, data for Analine-Acetic Acid System, Thole, Mussell, and Dunstan:
J. Chem. Soc., 103, 1 1 x 3 (19x1). * R. B. Denison: Trans. Faradav SOC.,8, 20 (1912).
3Thole, Mussell, and Dunstan:"J. Chem. Soc., 103,1 1 1 4 (1913).
ACETIC ACID-STANNIC CHLORIDE SOLCTIONS
I427
Electrical Conduclivzty of Solutions :-Electrical specific conductivities of the solutions were measured by the usual Kohlrausch bridge method. The conductivity cell was standardized with a 1/50 normal solution of KC1. The experimental specific conductivities are shown in the fourth column of Table I. They are plotted against mol fraction concentration in Fig. 5 . The specific conductivity is a function of the ion concentration, the ion mobility, and the viscosity. The first of these factors probably accounts for the initial rapid increase in conductivity, while the rapid increase in viscosity undoubtedly accounts for the subsequent decrease in conductivity. 30
20
k P
i
/O
___---
MOL FRACTION O f JNC/4
FIG 5
Other things being equal, it is known that the ion mobility is inversely proportional to the pth power of the viscosity, where p is a constant dependent upon the nature of the ion. I n those cases for which p is known its value is not far from unity.l If we assume the exponent to be unity, the conductivity can be corrected to the viscosity of the pure solvent (acetic acid). The second curve of Fig. j shows the molar conductivity so corrected. For most sabstances the molar conductivity corrected to the viscozity of the pure solvent continually decreases with increasing concentration. The fact that the molar conductivity here increases indicates either that the dissociation is increasing or that the nature of the ion is changing. The formation of more mobile ions is hardly consistent with the interpretation given the marked viscosity incn:ase and volume contraction, namely, an increase in association. I t therefore seems probable that the increase in molar conductivity indicates an inKraus: “The Properties of Electrically Conducting Systems,” I 14 (1922).
1428
J. D . STRAKATHAS AND J O H S STRONG
crease in dissociation. This is in agreement with the hypothesis advanced by Kendall' that dissociation in solution is preceded by association, in that the two phenomena do accompany one another here. Summary :-The viscosities, electrical conduct,ivities, and .specific volumes of solutions of stannic chloride in acetic acid have been measured for various concentrations of SnCli up to that for which the mixture breaks into two layers. The mixing is accompanied by large volume contraction and heat evolution. The volume contraction a t certain concentrations amounts to 3 2 , 1 0 7 ~ of the volume calculated from a weighted mean of the component specific volumes. The curve relating viscosity to concentration has a very marked maximum. The maximum deviation of the measured viscosity from that calculated from a weighted mean of the component viscosities is remarkable large. The maximum is 2 8 2 times as great as that calculated from the additive law; it is 263 times the viscosity of the most viscous component. The maximum of the 'viscosity curve, and therefore the maxiniuni deviation of viscosity from that calculated from a weighted mean of the coniponent viscosities (since the component viscosities are negligible as compared to the solution viscosity), occurs accurately at a concentration of 0 . 2 j . The position of the maximum is probably independent of temperature. I n view of the extremely large deviation of viscosity from the additive law, the accuracy with which the peak falls a t the concentration corresponding to the compound SnCl4.3CH3COOH, and the unusually great volume contraction and heat evolution upon mixing, it seems logical to attribute the marked change in properties with concentration to the formation of a compound SnCla.3CH3COOH. rnzcerszty of Kansas. M a y 28, 1987. I Kendall, Rooge, and .indrews: J. Am. Chem. Poc., 39,2302 (1917); Iiendail and Rooge: 39, 2326 (1917).
