EFFECTS OF DISSOLVED SUBSTANCES OK T H E SOLGTIOK TEMPERATURE OF A P H E S O L - K d T E R SYSTERI BY J. L. CULBERTSON A N D E . S. PALMER
Introduction Since the time of Hofmeister' numerous studies have been made of the so-called Hofmeister or lyotropic ion series. Various explanations of the lyotropic action have been offered, the earliest of which was the theory that the different degrees of hydration of the ions was responsible for the varying magnitude of their effects on aqueous systems. Buchner? studying gelatin gels concluded that polyhydrol molecules of water had a greater peptizing influence than simple H20 molecules. Hence the ions would appear to influence the association of water. Gortner and his co-workers3 extracting protein from wheat flour with potassium halide solutions obtained results which agree with the conclusions of Buchner. Kruyt and Robinson4 determined the solubilities of quinone, hydroquinone, and various nitroanilines in aqueous inorganic salt solutions. The distinct lyotropic series found for the salts is explained by postulating orientations of several kinds in the neighborhood of the ions and the molecules of the solute. The present investigation was made to determine the effect of dissolved substances on the solution temperature of a phenol-water mixture having a weight ratio of 36:64. Preliminary study of the system by Chlbertson and Graftonj indicated the probable trend of results of such an investigation. Taylor6 found that inorganic salt solutions in their effect on the solution temperature of phenolwater systems formed a lyotropic series. The present investigation was initiated for the purpose of studying the effects of a group of dissolved substances on this system over a considerable range of concentrations. Experimental X a l e r i a l s . llallinckrodt C. P. quality phenol was redistilled and both the first and last portions rejected. This purification was deemed sufficiently thorough to permit recovery of the used phenol from the salt containing aqueous solutions by two such fractional distillations. The salts were used as found in the original containers. The KCl, KI, KXO1, and KCKS were Rlallinckrodt's C. P. quality, the KBr was Merck's C. P. quality, and the li,SOa were Eaker's (1. P. quality. F. Hofmeister: Arch. exp. Path. Pharm., 24, 247-60 (1888). * E .H. Buchner: Rec. trav. chim., 46, 439-44 (1927). R. A. Gortner, W. F. Hoffman and K. B. Sinclair: Colloid Symposium Monograph, 5 , 179-98 (1928). H. R. Kruyt and C. Robinson: Proc. Koninklijke Akademie van Wetenschappen, Amsterdam, 29, 1244-50(1926). J. L. Culbertson and C. M . Grafton: 1927, Unpublished data. 6 FV, IF'. Taylor: Proc. Roy. SOC.,Edinburgh, 49, Pt. 3, 198-209 (1928-29).
J. L. CULBERTSOX A S D E . S . PALXER
3064
The organic acids used, malonic and succinic, were Merck's C. P. quality and were used directly from the original containers. Apparatus. h test tube large enough to admit a thermometer, the latter graduated to tenths of a degree, and a spiral glass rod for stirring purposes, was immersed 10-12 cm. in a variable temperature bath. Means of slowly heating or cooling the bath under close control were provided. Uniform agitation of the phenol-water system contained in the test tube was found necessary and was provided by imparting a reciprocating motion to the glass spiral by means of an electric motor. Procedure. In all experimental work the basic phenol-water solution consisted of a 36:64 weight ratio. A quantity of this solution was placed in the inner tube of the apparatus and the solution temperature obtained by slowly heating the bath with continuous agitation of the mixture. Since the solution temperature is determined by observing the change from an opaque to a clear system an arbitrary condition of transparency must be chosen. Such a condition represented by a solution temperature of 65.6'C. was selected as permitting greatest accuracy. Iluplicate determinations showed an agreement of 10.1'.
TABLE I KC1
KRr
Salt
Temp. Rise
Conc.
jo'c'.
0.118
0.
0.248
1.15
0.509 0.857
2,so
1.022
I .884 2.072
4.165 7.894 11.999
2 .oo
3.50 5.77 6.38 10.46 18.66 26.76
KKOa
Salt
Conc. O.II.+
Temp. Rise 0 .j o o c .
1.30 0,490 1 50 0.7jI 2.8j 3 .60 0.993 j.86 1.685 6,j3 1,975 3.973 II.4j 18.41 7.01' 0.272
'
12,070
31.0
Temp. Rise
Temp. Rise
0.131
0.50"C.
0.062
0.252
0.85
0.I2j
0.236 0.346 0,519
3.20
1.028
5 . 7 2
0.546
1.50 2.0:
0.998 1.397
2.jj
2.253
4.038 8.181 16.011
Temp. Rise
o 163
0.6j'C. 0.95
0 2j2 0 0
513 714
I 000
o.4j0C. 1.o.j 1.6j 2 . IO
3.15 4.81 7.98 13.99
2.0j4
9.72
4.008 6.002
16.63 21.18
25.0'j
8.020
29.7-b
1.45
1.90 2.55
56j
3.15
2 048
4.40
4 023 7 997 I 6 045
7.63 13.05 21.95
I
KCNS
KzS04 Conc.
Conc.
0.jjI
KI Conc.
Conc
o 260 0 5oj I 063 2 013 4 724
8 229 16 006
Temp. Rise
o 32OC. jo o 6j 0 95 0
I
15
I 45 I
8j
SOLUTION TEMPERATURE O F A PHEKOL-WATER SYSTEM
3065
After the solution temperature of the pure phenol-water system was determined a new mixture was prepared from a known weight of the basic solution and a small weighed quantity of one or more additional substances. The new solution temperature was determined and the temperature rise induced by the added substances was noted. Results. I. Effect of Dissolved Salts on the Solution Temperature of the basic
FIG.I
FIG.z
Six inorganic salts were studied by the methods outlined above. The results obtained are given in Table I. These data are represented graphically by Fig. I . Concentrations in all experimental results in this paper are expressed in milliequivalents per I O grams of phenol. I t should be noted that the lower concentrations included in the table are not plotted in the figure because of limitations imposed by the coordinate scales used. It may be mentioned that check runs over several hours time proved that errors resulting from evaporation mere negligible.
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J. L. CULBERTSON AND E. S. PALMER
11. Effect of Malonic and Succinic Acids on the Solution Temperature of a Phenol-Water System. These data were obtained by adding a definite quantity of a salt (as indicated in the table) to a 36Yc phenol-water solution and determining the solution
CONCENTRATION
IN M ~ L L ~ E ~ U I V A L E N IPSE R 1 0 C R ~ M SP H E N O L
FIG.3
TABLE I1 Malonic Acid
Succinic Acid
HOOC-CHrCOOH
IIOOC-CH2-CH2-COOH
K X 0 3 * = 0,750 milliequivalents per Conc. Acid 0.0279
0.0;96
grams of phenol throughout Temp. Rise Temp. Rise by Acid by Acid and Salt 1.96 -0.04 -0.07 1.93
KC,** per
IO
Conc. Acid
= 0.890 milliequivalents I O grams of phenol
throughout Temp. Rise Temp. Rise by Acid by Acid and Salt
o 0301
-0.02
3.30
0.0593 o.oij8
-0.06
3.26 3.25
0.2392
-0.20
1.80
0 . j009
-0.36 -0 4j
1.64 1.55
0 .IO02
-0.
IO
3.22
0.2198
-0.18
-0.8j -1.82
1.1;
0.3'ji 0.4366 o.gj30 1.3'5 1 764 2 583 3.332
-0.24 --0,34 -0.42
3,14 3.08
0.6360 I , 137 2.3jo
0.18
2,614
-2.08
-0.08
2.852
-2.25
-0.2 j
-0.07
2.98 2.90 1.92
-1.40
98
'
--I
'
-3.14 -4.17
1.34 0.18
-- 0 . 8 5
* The temperature rise of this mixtures was 2.00' before the acid was added. ** The temperature rise of this mixtures was 3.32'.
SOLUTION TEMPERATURE O F A PHENOL-WATER SYSTEM
3067
temperature. A small weighed quantity of one of the organic acids was then added to the solution and the change in the solution temperature was noted. A Beckmann thermometer was substituted for the tenth degree thermometer used in the above work thus giving an accuracy of i o . 0 jo. The results are tabulated in Table I1 and illustrated graphically in Figs. z and 3. Portions of the curves showing low concentrations of the KCl and KXOa are also included for comparative purposes and to aid in locating the origins of the acid curves.
Discussion Fig. I indicates clearly, throughout the concentration range employed, the usual lyotropic anion series, the magnitude of the effect of the separate ions being in the order of SO1 >C1 >Br >NO3 > I >CSS. Quantitatively the differences between ions are not at all uniform as the results of other investigations of lyotropic action show. Kruyt, in the investigation noted above, attributes the lyotropic action of salts to the orientation of water molecules around the ion, together with the undoubted differences in degree of hydration of the ions. I t is our desire to correlate the effects of this series of ions with an additional property of such systems and for this purpose we have determined the effects of the malonic and succinic acids on two of the pheriol-water-salt systems. As shown in Fig. z the malonic acid was added to a phenol-water-potassium nitrate mixture whose solution temperature was z.o°C. above that of the standard phenol-water system. Similarly the succinic acid was added to a phenol-wter-potassium chloride mixture whose solution temperature was 3.3z°C above that of the standard mixture. (See Fig. 3). K i t h increasing concentration of the acid in each case the solution temperature is lowered until within the concentration ranges employed it drops below the solution temperature of the standard mixture. In the interpretation of these results, attention is called to the values of the surface tensions of the aqueous solutions of the salts and acids used. These values are shown in Fig. 4. Those for the salt solutions were taken from International Critical Tables' while those for the acids are due to King and Kampler .z I t would appear that a proper interpretation of the surface tension values should also be capable of application to the solution temperature effects noted. The orientation of water molecules in itself cannot account for the increased surface tension of the salt solutions, for orientation when it occurs must of necessity tend to reduce surface tension. This does not however indicate that water molecules cannot, be oriented by the ions present for the ions due to their polar character would be expected to enhance surface energy values. The increase however would be minimized by any orientation which occurs. The organic acids being less polar in character than water itself International Crit. Tables, 4, 466.
* H. H. King and R. W. Wampler:
J. Am. Chem. SOC.,44, 1894-1902(1922). Kote: Concentrations are expressed in terms of molal values in the article to which reference is made. In Fig.4, they are plotted as molar concentrations. The resultant error does not change the general relationships.
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J. L. CULBERTSON AND E. S. PALMER
cause lowered surface tensions in their solutions. These relations are qualitatively in agreement with the effects of the dissolved substances on the solution temperatures. According to Harkins’ when two highly immiscible phases are in contact the interfacial tension is high. Lower interfacial tensions accompany greater mutual solubility. I t is no doubt permissible in this case to assume that the salts which increase the surface tension of the water phase-air interface also
FIG.4
increase the water phase-phenol phase interfacial tensions and that the organic acids decrease this interfacial tension. We would then conclude from the results of the present investigation that the solution temperatures of the aqueous solution-phenol systems are in direct dependence upon the surface tensions of the aqueous solutions involved. I t does not follow however that solubilities and therefore interfacial relationships in such cases may always be predicted from free surface tensions. Illustrating this point in the field of colloidal solutions is the fact that casein is made more soluble in water by the presence of the iodide ion. Following the ideas of Kruyt’ we would conclude 1
W. D. Harkins, F. E. Brown and E. C. B. Dnvies: J. .4m. Chem. Soc., 39, 354, 541
(1917).
* H. R. Kruyt: “Colloids,” translated by H. S.van Klooster, 2nd Ed., p. 2j8.
SOLUTION TEMPERATURE OF A PHENOL-WATER SYSTEM
3069
that in such cases the nature of the orientation of the water molecules is such that interfacial energies are lowered by the presence of the ion in spite of free surface tensions that are higher than that of water. We propose to study the interfacial tensions of the water-phenol and other systems in order to test the relationships suggested here.
Summary The effect of a number of dissolved substances upon the solution temperature of a phenol-water system has been determined. 2 . The relationship of these values to the surface tensions of the aqueous solutions is noted and an interpretation suggested. I.
The Department of Chemistry, Stale College of Washington, Pullman, Washington.
