Aqueous Solutions of Sodium Benzenesulfonate and Monosubstituted Derivatives SOME PHYSICOCHEMICAL PROPEWTIES PAUL W. RENICH AND ROBERT TAFT Kansas Wesleyan University, Salina,Kart., a n d University of Kansas, Lawrence, Karc.
Derivatives of sodium benzenesulfonate are commercialll- available and are used as surface active and hydrotropic agents. Data on the physical properties of aqueous solutions of all members of this group are virtually lacking in the literature. This study was undertaken to supply this lack of information regarding the parent substance and four of its simpler derivatives (the C1, OH, SH2, and CH3 substituents); the study is being continued on the common sodium xylenesulfonates. Properties measured included density, viscosity, surface tension, refractive index, solubility, and conductance over a range of concentrations which in general varied from 0.005 molal up to and including 1.0 molal at Oo, 25', 45', and 60' C. Freezing point depressions were also determined. The physical properties determined for these five salts do not in general deviate from those usually found for organic salts in water, although the solubility of sodium p-methylbenzenesulfonate differs appreciably from the remaining four salts. No evidence was found of micelle formation in solutions of any of the salts.
F
EW data are available on the physical properties of aqueous solutions of sodium benzenesulfonate solutions or of the monosubstituted derivatives of this sulfonate. Rhodes and Lewis ( 2 0 ) and Hauslich ( 6 ) have determined the solubility of sodium benzenesulfonate in water a t various temperatures; however, their figures do not agree with each other. Ostwald (17) and Jeffery and Vogel ( 1 2 ) have determined the equivalent conductance of sodium beiizenesulfonate, but again the data of these two sets of investigators do not agree. Of monosubstituted derivatives, there are only very incomplete data on physical properties of their solutions. As derivatives of sodium benzenesulfonate are used as surface active and hydrotropic agents and are available commercially, certain physical properties of a number of these compounds have been systematically studied. Included in those selected for study were not only simple derivatives of sodium benzenesulfonate, the parent substance of all aryl benzenesulfonates, but those of the common sodium xylenesulfonates. It is hoped eventually to extend the study to still higher members of the group. The present paper reports a study on sodium benzenesulfonate and some of its simpler derivatives. Compounds whose solutions were selected for study included sodium benzenesulfonate, sodium p-chlorobenzenesulfonate, sodium p-toluenesulfonate, sodium p-hydroxybenzenesulfonate, and sodium p-aminobenzenesulfonate. The properties measured were density, viscosity, surface tension, conductivity, refractive index, depression of freezing point, and solubility. These properties were determined on solutions ranging in concentration from 0.005 molal up to and including 1 molal or the limit of the solubility, whichever was smaller. ,411 measurements except the depression of the freezing point were carried out a t four different temperatures, O', 25', 45', and 60" C. The solution for each concentration was prepared directly by weighing out the salt and water used. All weighing8 were made to four significant figures, applying the usual corrections for weighing in air. A
sufficientamount of solution was prepared so that all the properties except solubility could be measured using the same solution. Frequently a duplicate solution was prepared and measurements were made to verify the accuracy of both the preparation of the solution and the individual measurements.
811 compounds except sodium p-aminobenxenesulfonate were obtained from the Eastman Kodak Co., but were found to contain varying quantities of sodium chloride and other impurities. Sodium p-aminobenzenesulfonate was prepared by adding a calculated quantity of concentrated sodium hydroxide Eolution to a concentrated solution of pure sulfanilic acid. All compounds were purified by recrystallization from absolute alcohol until there was no further change in the conductivity of 0.01 molal solutions on successive recrystallizations Several of the salts required four to five recrystallizations. The salts containing excessive amounts of foreign material and colored impurities were first extracted several times by means of absolute alcohol in a Soxhlet extraction apparatus. All the salts when purified were white crystalline solids and all were stable. After recrystallization, all salts except sodium p-aminobenzenesulfonate were dried in an oven maintained at 110' to 120" C. Sodium p-aminobenzenesulfonate was dried at 50" C. under reduced pressure because of its tendency to decompose at temperatures above 100" C. DENSITY
Densities of the various solutions were determined by the use of a Parker pycnometer (19). The volume of the pycnometer capillaries was determined by filling each capillary with mercury, weighing the mercury, noting the temperature, and calculating the volume. The pycnometers a-ere standardized at each temperature of measurement by means of distilled water. At all temperatures other than 25" C. the pycnometer was allowed to stand for 0.5 hour o r longer at room temperature before it was prepared for weighing. The exterior of the pycnometer was Rrashed with water and finally with acetone to remove any oil film from the glass surface. It was then placed inside the balance case and allowed to come to equilibrium for 0.6 hour before weighing. Each time a different solution was measured, the interior of the pycnometer was cleaned
2376
October 1951
INDUSTRIAL AND ENGINEERING CHEMISTRY
with cold chromic acid, rinsed with distilled water, and dried with absolute alcohol. The densities were calculated using the following equation:
where
n1
'
= absolute viscosity of liquid to be measured
absolute viscosity of standard (water) density of liquid density of standard at temperature of determination and t 2 = time of flow of liquid and standard, respectively
n2 = dl = d2 = tl
where D = density of liquid SI = mass of pycnometer plus liquid weighed in air S, = mass of pycnometer weighed in air S, = mass of pycnometer plus water weighed in air d, = density of water at temperature of determination u = density of air at temperature of determination and barometric pressure at time of weighing
2311
This equation is strictly true only when the time of flow is large and the differences in viscosity between the reference liquid and the unknown are small. These conditions are fulfilled
The densities of water were taken as 0.99987 a t 0" C., 0.99707 at 25" C., 0.99024 a t 45' C., and 0.98324 a t 60" C. (8). The average values of the densities of the solutions a t the various concentrations and the four temperatures are given in Table I and graphically for sodium benzenesulfonate in Figure 1.
0.25 Molnlity
00
of
050 0 75 Sodium Benzene Sulfonate
Figure 2. Absolute Viscosity of Sodium Benzenesulfonate
TABLE I. DENSITIES (Grams per ml.) Molality
of Sodium Benzene Sulfonote
Figure 1. Density of Sodium Benzenesulfonate
Concentratration, Molality
0.005
The p-chloro compound, which had the highest molecular weight, gave solutions of the greatest density. Sodium benzenesulfonate with the lowest molecular weight, however, did not give the lowest densities, for these were given by sodium ptoluenesulfonate and were only slightly less than the densities of sodium benzenesulfonate. The other two compounds, sodium p-aminobenzenesulfonate and sodium p-hydroxybenzenesulfonate, gave densities which lay between those of sodium p-chlorobenzenesulfonate and sodium benzenesulfonate. VISCOSITY
The viscosities of the various solutions were determined with a n ordinary Ostwald viscometer, selected so that it would require a t least 1 minute for distilled water to pass through the capillary a t 60" C. The viscometers were cleaned before each determination with chromic acid, washed thoroughly with distilled water, and dried with absolute alcohol. They were calibrated with distilled water a t each of the temperatures used. In order that the height of the liquid column would be the same in every case, 5 ml. of the solution were used in each determination. To make sure that the viscometer was vertical for all determinations, it was aligned with two vertical lines drawn on the glass wall of the constant temperature bath. The times of flow were determined with a stop watch which could be read to 0.1 second. The stop watch was checked with an electric clock and found to be in error by less than 1 second in 5 hours. Readings were taken until several values checked within 0.1 to 0.2 second. Relative viscosities were calculated from the following equation: nl =
&
n2
dztz
0.010 0.050 0.100 0.250 0.300 0.750 1,000
Temperature
0" c. 25' C. 430 c. SODIUMBENZENESULFOSATE
60' C.
1.0004 1.0008 1.0042 1.0081 1.0200 1.0389 1.0565 1 0733
0.9838 0.9840 0.9869 0.9905 1.0010 1.0178 1.0334 1.0483
0 9976 0.9978 0.0010 1.0047 1 0158 1.0335 1.0499 1.0656
0.9908 0.9910 0.9939 0 997i
i.008s 1 0253 1.0412 1,0564
SODIUM P-CHLOROBENZENESULFOA-ATE 0,005 0,010 0.050 0.100 0.250 0.500 0.750
1,000
1.0004 1.0010 1.0053 1.0104 1.0256 1.0494 1.0719
...
0.9976 0.9981 1.0021 1.0069 1.0212 1,0435 1.0646 . I .
0,9907 0.9912 0.9950 0.9997 1.0135 1.0350 1.0554 1.0746
0,9837 0.9843 0.9879 0.9926 1.0061 1.0272 1.0472 1.0662
SODIUM p-MIOTHYLBENZENESULFONATE 0.005 0.010 0.050
0.100 0.250 0.500 0.750 1.000
1.0005 1.0008 1.0041 1.0080 1.0197 1.0380 1.0550 1.0712 SODIUM
0.005 0,010 0.050 0.100 0.250 0.500 0,750 1.000
0.9976 0.9979 1,0009 1.0046 1.0153 1.0323 1.0481 1.0631
0,9907 0.9910 0.9939 0.9974 1.0077 1.0241 1.0393 1.0538
0.9837 0.9841 0.9869 0.9904 1.0004 1.0164 1.0313 1.0454
p-HYDROXYBENZESESULPOXATIO
1.0004 1.0009 1.0047 1,0094 1.0232 1.0446
... ...
0.9975 0.9980 1.0016 1.0059 1.0188 1.0391 1.0584 1.0765
0.9907 0.9911 0.9945 0.9988 1.0113 1.0309 1.0498 1.0673
0.9837 0.9841 0.9873 0.9917 1.0040 1 ,C234 1.0419 1.0593
SODIUM p-AMINOBENZENESULFONAT~ 0.005 0.010 0.050 0.100 0.250 0.500 0.750 1.000
1.0004 1.0008 1.0043 1,0090 1,0220 1.0424 1.0617
...
0,9976 0.9979 1.0014 1,0056 1.0178 1,0370 1.0552 1.0724
0.9906 0.9910 0.9943 0.9984 1.0103 1,0289 1.0467 1.0636
0.9837 0.9842 0.9874 0.9915 1.0031 1.0216 1.0391 1.0557
INDUSTRIAL AND ENGINEERING CHEMISTRY
2378
TABLE 11. L
r
~
~
(Millipoises)
Concentlatlon
0" c.
AIola1,tj
SODIUM
17.99 18.07 18.39 18.75 19.93 21.98 24,20 26 64
0 005
0 010 0 05U 0 100 0 250 0 500 0 750 1 000
Temperature ~
~
260 c.
450 c
~
__~
Vol. 43, No. 10
Sodium benzenesulfonate had the lowest viscosity, while ~ ~ ~ highest. ~ Of the other ~ had the sodium~ p-chlorobenzenesulfonate three with approximately the same molecular weight, sodium p-aminobenxenesulfonate solutions gave the lowest viscosities.
60" C.
BEXZESEST:LFOX.ATE 8 98 8 99 9 is
9 32
9 80 10 73 11.70 12.73
5 98 5.99 6 09 6 19 6.48
7 05 7.62 8.25
4.71 4.71 4.79 4.86 5.08 5.50 5.92 6.38
75
c 71 0 I
18.05 18.07 18.41 18.91 20.34 22 82 25.53
0 005
0 010 0o x 0 loa 0 250 0 500 0 750
...
1 000
8.99 9.00 9.16 9.39 10.00 11.03 12.19
5.98 5.99 6.08 6.23 6.59 7.23 7.93 8.69
4.71 4.72 4.78 4.88 5.15 5.63 6.12 6.68
h
67
c
-
a)
63
m 59
18.05 18.07 18.41 18.93 20.40 23.00 25.92 29,lZ
0 006
0 010 0 050
0 100 0 250 0 500 0 750 1 000
8 99 9.00 9.16
9 41 10 02 11 13 12 35 13 68
5.98 5.99 6.09 6.26 6.61 7.28 7.99 8.79
4.71 4.72 4.79 4.91 5.16 5.64 6.16 6.74
55 00
0.25 Mololity of Sodium
0.50 p-chloro
0.75
IO0
Benzene Sulforole
Figure 4. Surface Tension of Sodium p-Chlorobenzenesulfonate
8 0 D I U M p-IiSDHOSYRESasXESULFO~ATE
18.03 18.07 18.39 18.69 19,86 21.94
0 005 0 010 0 050 0 100 0 250 0 500 0 7ZO
...
...
1 000
8.99 9 00 9,l5 9 31 9.88 10 85
11.96 13 21
5,98 5.99 6.08 6.20
6.56 7.15 7.86 8 60
4.71 4.72 4.79 4.87 5.14 5.60 6.11
18.03 18.08 18.37 18.66 19.75 21.69 24.08
...
8.99 9.00 9.15 9.30 9.84 10.76 11.74 12,81
5.98 5.99 6.10 6.20 6.54 7.10 7.71 8.38
Surface tensions of the solutions were measured by means of the capillary rise method.
6.66
SODIUM ~-A~~INORE~ZEN~SUI,~OS~TE
0 005 0 010 0 050 0 100 0 250 0 500 0 750 1 000
SURFACE TENSION
4.71 4.72 4.79 4.87 5.11 5.54 5.98 6.47
sufficiently to warrant the use of the equation for these solutions, The densities for water a t the temperatures in question were thc same as for the determination of density. The absolute viscosity of water in millipoises was taken as 17.94 at 0 C., 8.949 at 25' C , 5.970 a t 45" C., and 4.70 a t 60' C. ( 8 ) . The absolute viscosities a1t given in Table I1 and graphically for sodium benzeiiesulfonatc> in Figure 2 O
The capillary tubes were examined for uniformity of bore by inserting a small quantity of mercury into the capillary and noting the length of the column at various positions along the capillary t'ube. The diameters of the capillary tubes were determined by filling the capillary tube wit'h mercury and determining the weight of the mercury. Before each measurement the capillary tube was cleaned with chromic acid, rinsed thoroughly with water, and dried with absolute alcohol. The capillary tubes were placed in a tube approximately 5 em. in diameter containing the solution, and then placed in the constant temperature bath. Readings were taken by means of a telescope mounted on an adjustable scale with a vernier and accurate to 0.1 mm. The average height of the capillary rise was in the neighborhocd of 5 to 6 cm., so that the accuracy attainable on the readings was about 1 part in 500, exeept on the more concentrated solutions where it lvas about 1 part in 300. Using the equation (2,441 y2 = hgpzr, the surface tension for water was calculated at the four temperatures employed. They T7ei-e found to agree n.ithin 1 part in 300 wit'h Internat,ional Critical Tables values (9). The International Critical Tables values mere used in the equation:
79
ahere yz = surface tension of water at temperature of determirlntion hl = height of capillaiy rise of solution measured p1 = density of solution measured hz = height of capillary rise cf water y1 = surface tension of unknon n solution p L = density of water (as given in section on density)
75
-
71
3 0" 67 I
63
.. Lo
59
55 Molality of S o d i u m
Figure 3.
Benzene Sulfonate
Surface Tension Values of Sodium Benzenesulfonate
As hi and hZ as well as PI and p2 are of the same order of magnitude, the well-known correction terms, such as those mentioned by Harkins (24), would cancel out, because the same capillary was used for both water and the solutions. The International Critical Tables (9) values used for the surface tension of water in dynes per em. are 75.64 at 0" C., 71.97 a t 25" C., 68.74 at 45" C., and 66.18 a t 60" C. The calculated values obtained for the solutions studied are found in Table 111 and graphically in Figures 3 through 7. All the salts Ion-ered the surface tension markedly in dilute solutions, but at concentrations between 0 05 and 0.10 molal,
~
INDUSTRIAL AND ENGINEERING CHEMISTRY
October 1951
2319
TABLE 111. SURFACE TENSION (Dynes per om.) Concentration Molalit;
00
c.
250
Temperature 450
c.
c.
60’ C.
SODIUM BENZENESULFONATE
0,005 0.010 0.050 0.100 0.250 0.500 0.750 LOO0
75.2 75.1 75.1 75.0 74.0 72.3 71.1 69.8
71.6 71.5 71.4 71.3 70.2 68.9 67 8 66.5
68.5 68.4 68.3 68.2 67.2 66.1 64.9 63.9
66.1 66.0 66.0 65.8 64.8 63.9 62.8 61.6
SODIUM p-CHLOROBENZENESULFONATE 0.005 0.010 0,050
0,100 0.250 0,500
0,750
Sodium P - m e t h y l b e n ~ e n e i u l f o n o t e
Mololtfy Of
CONDUCTIVITY
The point of balance was determined by earphones tuned to 1000 cycles per second. The slide-wire contact was set in the middle of the bridge for all final readings, to eliminate an error due to the difference in capacity of the two parts of the s l i d k n e . The resistance of the cell was then given directly by the adjustable resistance. The adjustable resistance was calibrated against a variable standard resistance which had been calibrated by the Kational Bureau of Standards. This calibration was done by placing the standard resistance in the circuit in place of the conductivity cell. A variable condenser was placed across the adjustable resistance to balance the capacity of the conductivity cell in order to obtain a sharp minimum. At higher concentrations and higher temperatures this capacity was appreciable,
I MOlOll1y
I
1
0.50 0.75 Of Sodium p - hydroty Banran0 Sulfonota
IO0
I
I
0.005 0.010 0.050 0.100 0,250 0.500 0.750 1.000
I
I
Figure 6. Surface Tension of Sodium p-Hydroxybenzenesulfonate
65.6 65.5 65.2 64.6 63.0 60.9 58.9 57.2
74.8 74.7 74.6 73.5 71.6 68.5 65.8 63.7
71.5 71.3 70.4 69.7 67.9 64.8 62.5 60.4
68.3 68.2 67.4 66.7 64.9 61.9 60.0 58.0
66.1 66.0 65.2 64.5 62.9 60.2 57.9 56.0
SODIUM ~-HYDROXYBENZENESULFONATE 0,005
0,010 0.050 0,100 0.250 0,500 0.750
1,000
74.9 74.9 75.0 74.9 74.8 75.3
71.4 71.3 71.4 71.4 71.4 71.6 71.5 71.7
... ...
68.3 68.2 68.3 68.5 68.8 68.8 69.0 69.2
66.1 66.0 66.1 66.0 66.5 66.6 66.9 67.0
SODIUM p-AMINOBENZENEBULFONATE 0.005 0.010 0.050 0.100 0.250 0.500 0.750
1,000
Conductivity measurements were made by a Kohlrausch bridge with an electrically driven tuning fork of 1000 cycles per second as the source of alternating current.
0.25
67.9 68.0 67.6 67.1 65.3 62.8 60.4 58.8
8 0 D I U M P-METHYLBENZENESULFONATE
especially a t lower temperatures, the surface tension rises and then falls. This curious effect, which is seen most clearly in Figures 4 and 5, is too great to be explained by experimental error. At still higher concentrations sodium benzenesulfonate, sodium p-chlorobenzenesulfonate,and sodium p-methylbenzenesulfonate all lowered the surface tension, while sodium p-hydroxybenzenesulfonate and sodium p-aminobenzenesulfonate actually increased the values above that of water as the concentration of the solute increased. Of all properties measured, the effect of substituted groups on the ring is greatest in the case of surface tension, taking sodium benzenesulfonate as the standard (for a 1 molal Rolution a lowering of about 5 dynes per em.). The authors find that p-chloro and p-toluene salts lower the surface tension about twice as much, while p-amino and p-hydroxy compounds increase it about 5 dynes per em.
I
71.0 70.9 70.7 70.1 68.1 65.6 63.0
1.000
Figure 5. Surface Tension of Sodium p-Methylbenzenesulfonate
0.0
74.9 74.7 74.8 73.8 71.5 68.9
74.9 74.7 74.9 75.0 75.5 76.0 76.4
...
’
71.4 70.9 71.3 71.3 71.7 72.2 72.5 72 8
67.8 67.6 67.8 68.2 68.8 69.3 69.6 70 0
65.6 65.2 65.4 65.8 66.4 67.0 67.3 67.7
and as there are ver few data on the capacity necessary in a conductivity bridge t i e values of the capacity necessary in the measurements of sodium paminobenzenesulfonate are given in Table V. The cells used were of the Henry type four different cells with different cell constants being used. The two with the lowest cell constants were purchased from Leeds & h’orthrup. The other two were designed and built in this laboratory and were similar to the purchased ones, except that they had two tubes for filling them. All cells were closed with glass stoppers and were immersed as completely as possible in the constant temperature bath to eliminate evaporation effects within the cell. Dip cells were tried originally, but it was found that many factors affected the resistance readings: the depth of the solution in the
I
63
Figure 7. Surface Tension of Sodium p-Aminobenzenesulfonate
2380
INDUSTRIAL AND ENGINEERING CHEMISTRY TABLE
Sodium Bensenesulfonate ConeenEquivalent conductance, dnormalitya mhos
-
Sodium p-Chlorobenzenesulfonate ConcenEquivalent tration, conductance, dnormalitv mhos
Vol, 43, No. 10
Iv. CONDUCTASCE
Sodium p-Methylbenzenesulfonate ConeenEquivalent tration, conductance, dnormality mhos cm.2 TEXPERATURE. , Oo C ~.
Sodium p-Hydroxybeneenesulfonate ConeenEquivalent Conductance, dnormality mhos cni.2 ,
.
Sodium p-Aminobenscncsulfonate ConomEquivalent $ration, , conductance dnormality mhos om.2
~
0.07069 0,9995 0.2231 0.3147 0.4940 0.6903 0.8355 0,9537
40.72 39.72 36.70 34,88 31.59 28.15 25.61 23.57
0.07069 0.09994 0,2230 0.3145 0,4933 0.6884 0.8322
39.70 38.51 35.55 33.72 30.40 26.86 24.28
0.07059 0,09980 0.2227 0.3142 0.4930 0.8329 0,9502
79.99 78,lO 71.79 68.36 61.70 55.18 50,48 46.76
0.07089 0.09980 0,2227 0,3140 0.4922 0.6864 0.8293
78.27 73.79 69,86 66.48 60.02 53.32 48.61
0.07035 0.09946 0.2219 0.3130 0.4911 0.6858 0.8294 0.9461
117.9 114.4 106.0 100.2 90.64 80.66 73.96 68.64
0.07034 0.09945 0.2219 0.3128 0.4904 0.6836 0.8257 0.9406
115.0 111.3 102.5 97.59 88.21 z8.35 41.55 66,43
0,07069 0.09995 0.2230 0,3145 0.4931 0.6878 0.8311 0.9471
38.98 38.18 35.22 33.38 30,03 26.53
0.07069 O,OYYY5
0.2230 0.3147 0.4938 0.6897
38.04 37.26 34.29 32.57 29.38 26.03
0.07069 0.09996 0.2230 0.3146 0,4936 0.6891 0.8334
38,74 87.82 3&15 33.44 30.30 27.08 24.41
74.44 72.84 66.75 63.42 57.12 50.68 46.31 42.49
0.07069 0.09980 0,2227 0.3141 0,4926 0.6873 0.8309 0.9472
75,72 73.71 68 25 64.99 58.78 52.50 48.10 44.46
109.3 107.0 99 .os 92.73 83.47 74.04 67.79 62.49
0.07035 0,09945 0.2219 0.3129 0.4907 0.6846 0.8275 0.9433
110.5 107,7 99.62 94.95 8," 72 16.65 70.32
2 3 . RR
Zi. 64
TEMPERATURE, 25' C.
0,6885
0.07069 0.09980 0.2226 0.3139 0.4920 0.6859 0,8283 0.9435
76.88 75,14 69.16 66.69 59.31 52.74 48.16 44,43 TEMPERATURE, 4 5 O C. 0 07035 113.1 0 09945 110.4 0 2218 101.6 0 3128 96,47 0,4902 87.13 0 6832 77.57 0 8248 71.15 0.9393 65.93
0,07069 0 I09980
0.2227 0,3141 0,4928 0,6879 0.8319 0.9487
0.07036 0.09946 0,2219 0.3130 0.4909 0.6851 0,8285 0,9446
65.15
TEMPERATURE. 60° C ~
0.07010 0.09911 0.2211 0.3119 0.4894 0.6833 0.8263 0.9425 a
149.5 145.0 132.8 126.8 114.5 101.7 93.35 86.57
0.07010 0.09910 0,2211 0.3117 0.4886 0.6811 0.8225 0.9369
146,2 142.4 130.4 123.9 111.7 98.99 90.67 84.15
0.07010 0.09910 0.2211 0.3117 0,4884 0,6806
0.8217 0.9355
Normality of all solutions used was calculated from equation: Sormality =
dip cell, evaporation of solution, and the distance between the electrodes and the bottom of the tube containing the solution. Cell constants were determined using Baker's analyzed potassium chloride, the two grades "low in SO4 and Pol' and "for calomel electrodes" giving identical results. The potassium chloride was fused in a platinum crucible and poured into a platinum dish to cool. It was then ground in an agate mortar and stored in a desiccator until ready to use. The 0.1 and 0.01 demal solutions recommended by Jones and Bradshaw (13) were used in determining the cell constants. The cell constants were measured at 0" and 25' C. and then calculated at 45' and 60" C. by means of the equation given by Washburn (as). All solutions were prepared from distilled water which was redistilled using ground-glass borosilicate glass equipment. Corrections were made for the specific conductivity of water on all calculations and solutions used. The specific conductivities for the water used were (mho per cm.) : 0" C. 1.4 X 25' C. 2 . 5 X 4 5 O C. 4 . 0 X 60" C. 5.0 X
10-6
10-8 10-0 10-0
These values did not change appreciably on standing for several days in a steamed and stoppered borosilicate glass flask. The cells were selected to give a measured resistance of not less than 100 ohms on any solution at any temperature. The equivalent conductances were calculated in the usual manner. Table V I gives the limiting equivalent conductances for the five salts at the four temperatures. Gunning and Gordon ( 5 ) give data from n-hich it is possible to establish the limiting equivalent conductances of sodium ion a t several temperatures. From these data the values are 39.76 mhos cm.2at 15" C., 50.11 at 25" C., 61.57 a t 35' C., and 73.79 at 45" C. Plotting these values and extrapolating give the limiting equivalent conductance a t 0" C. and 93.8 a t 60" C. of sodium ion as 26.5 mhos From these values for sodium ion, the limiting equivalent conductances of the anions studied can be calculated by difference from Table VI. Table I V lists the square root of normality and the equivalent conductance and the data for sodium benzenesulfonate are shown graphically in Figure 8. (The authors have
143,8 140.4 129.0 122.4 110.5 98.67 90.30 84.65
0.07010 139,l 0.07010 0,09911 135.9 0.09911 0,2211 125.6 0.2211 0.3119 117.4 0.3118 0.4891 105.6 0.4890 0.6826 93.58 0.6822 0,8264 85.87 0.8245 0.9410 79.43 0.9398 molality of salt X 1000 X density of solution/1000 weight
+
140,2 136.5 125.8 119.9 108I2 96.92 88.85 82.37 of salt.
also calculated a "corrected" equivalent conductance by multiplying the equivalent conductance values tabulated by the relative viscosity of each solution in question. The corrected equivalent conductance actually passes through a minimum when plotted against the square root of the normality for sodium benzenesulfonate at a given temperature.) As all these salts were purified to constant conductivitjrthat is, the measured resistance of a 0.01 molal solution did not change more than 2 parts in 1000 on successive recrystalliaationr of the salt-and as it was easily possible to duplicate this accuracy on any given solution, it is felt that the specific conductivities are accurate to about 0.27,. The present work on sodium benzenesulfonate is compared with that of Ostwald (17) and Jeffery and Vogel ( 1 % )in Figure 9. The actual values obtained for the equivalent conductance lie between the other two sets of data. However, the limiting
2381
INDUSTRIAL AND ENGINEERING CHEMISTRY
October 1951
TABLE VII. REFRACTIVE INDEX, nD Concentration, Molality
00
c.
250
Temperature 450
c.
c.
60' C.
SODIUM BENZENESULFONATE 0.005 0.010 0.050 0.100 0,250 0,500
0.750 1.000
1.3342 1.3345 1.3354 1.3369 1.3415 1.3489 1.3556 1.3615
1.3327 1,3329 1.3339 1.3354 1.3398 1.3467 1.3530 1.3591
1,3299 1,3301 1.3311 1.3326 1.3368 1.3437 1.3500 1.3560
1.3273 1.3275 1,3285 1,3301 1,3343 1.3410 1.3471 1.3332
S O D I U h l p-CHLOROBENZENESULFONhTE
o f Sodium
0.005 0.010 0.050 0.100 0.250 0.500 0.750 1.000
Benzene Sulfonafe
(3) Data of Jeffery and Vogel (4) Data of Ostwald
equivalent conductance as determined by extrapolation of the authors' curve is somewhat lower. The value determined by the present work is 84.8. Jeffery and Vogel give their value as 86.33. Ostwald does not list his, but from Figure 9 it appears to be almost exactly 86.0.
0.005 0.010 0.050 0.100 0,250 0.500 0.750 1,000
c.
0.00 0.04 0.42 0.33 1.85 1.40 2.40
.~.
Temperature 250 c. 450 c. 0.00 0.04 0.12 0.24 0.85 2.00 1.95 1.15 7.50 4.70 3.90 3,l5 4.60 5.65 5.86 7.10
Sodium Benzenesulfonate 43.4 84.8 127.1 162.0
Sodium p-Chlorobenzenesulfonate 43.0 84.2 125.0 156.8
1,3299 1,3302 1,3317 1,3332 1.3379 1.3452 1.3521 1.3588
1,3274 1,3278 1.3292 1.3308 1.3354 1.3424 1,3492 1,3559
0.005
1.3342 1.3345 1.3358 1.3375 1.3422 1.3501 1,3570a
1.3327 1.3330 1.3342 1.3358 1.3408 1,3480 1.3550 1,3620
1,3300 1,3303 1,3317 1,3332 1,3379 1.3453 1.3522 1.3589
1.3274 1.3278 1.3291 1.3307 1.3354 1,3424 1.3493 1.3558
Sodium Sodium Sodium Aminop-Methyl- p-Hydroxyt-enzenebenzenebenzenesulfonate sulfonate sulfonate 41.2 40.8 40.2 78.9 81.3 80.5 116.7 118.8 120.5 147.2 150.3 152.1
REFRACTIVE INDEX
The refractive indexes were determined by the use of an Abbe refractometer. Water u'as circulated through the refractometer by means of an electric circulating pump from a constant temperature bath. The refractometer was calibrated by means of distilled water at each of the four temperatures. The values used for this calibration, taken from the International Critical Tables (II), were 1.3340 for 0" C., 1.3325 for 25" C., 1.3298 for 45' C., and 1.3272 for 60' C. for nD. The values found are recorded in Table VI1 and are presented graphically for sodium benzenesulfonate in Figure 10. FREEZING POINT DEPRESSION AND SOLUBILITY
The freezing point depressions were determined by means of a freezing point thermometer which could be read to the third decimal place.
...
SODIUM p-.4MINOBEXZENEsULFOXATE
1.3342 1.3344 1,3360 1.3378 0.100 0,250 1,3432 1.3518 0.500 1 , 3600a 0.760 1,3670 1,000 Supersaturated. 0,005 0,010
60' C.
TABLE VI, LIMITINGEQUIVALENT CONDUCTANCES Temp., C. 0 25 45 60
1.3326 1.3329 1,3342 1.3359 1.3409 1,3482 1.3554 1.3620
0.050
0.12 0.28 2.80 2.50 9.50 3.85 5.75 7.40
1.3275 1,3278 1.3290 1.3308 1,3356 1,3432 1.3507 1.3573
1.3341 1.3344 1.3359 1,3376 1,3428 1.3508 1,3578 1.3647
0.050 0.100 0,250 0.500 0.750 1.000
CAPACITIES USED TO BALANCE BRIDGEON SODIUM p-AMINOBENZENESULFONATE
00
1,3301 1.3303 1.3316 1,3333 1 ,3384 1,3462 1.3534 1.3600
0.005 0.010 0.050 0.100 0,250 0.500 0.750 1 ,000
0.010
(Readings i n microfarads X 109 Concentration, Molality
1,3327 1,3330 1,3342 1.3360 1.3411 1.3490 1,3568 1 ,3630a
SODIUM p-METHYLBENZENESULFONATE
Figure 9. Equivalent Conductance of Sodium Benzenesulfonate at 25 a. c.
TABLEV.
1.3342 1.3345 1.3357 1.3374 1.3429 1.3512 1. 3 5 m 4
a
1.3327 1,3329 1.3344 1,3361 1,3414 1.3500 1,3580 1.3653
1,3300 1.3302 1.3318 1.3335 1,3387 1.3469 1.3549 1,3621
1.3273 1.3276 1.3291 1.3308 1,3360 1.3441 1.3520 1.3591
The solution whose freezing point was to be determined was placed in a large test tube which contained about 25 ml. of the solution. A freezing point thermometer and a glass stirrer were placed in the test tube. The tube containing the solution, thermometer, and stirrer was then placed in a larger glass tube allowing about 0.5 inch of air space between the two tubes, The large glass tube was then placed in the freezing bath, which was held a t a temperature 0.1' C. lower than the freezing point of the solution to be determined. The stirrer was moved slowly up and down at a constant rate of 30 short strokes per minute. The freezing point was taken when there was only a very small amount of solid separated out; this value could most easily be obtained by separating out a larger amount of solid and then lifting the tube to warm it slightly, after which it was allowed to come to equilibrium. This same procedure was used to determine the zero point of the thermometer with distilled water, By following the above procedure closely, the readings could be duplicated within 0.002' or 0.003" C. Values found are given in Table VIII. On all the compounds except sodium benzenesulfonate readings were obtained on the eutectic temperature, using the 1 molal or less concentrated solutions. The solubilities were determined by extrapolation of the refractive indexes obtained as described above to the refractive index of the saturated solution. The refractive index of the saturated solution was found in the following way: A 250-ml. flask fitted with a mechanical stirrer and an opening for the introduction of salt and the removal of solution was immersed in the constant temperature bath. The apparatus for removal of solution was a small tube with a filter in the bottom and fitted with an eye dropper so that the solution could be sucked back into the tube or by means of pressing on the
INDUSTRIAL AND ENGINEERING CHEMISTRY
2382
dropper could be forced out through the filter. The mixture of salt and water was stirred at the constant temperature for approximately 4 hours before the first reading was taken. Successive readings were taken every 2 hours until there was no change in the refractive index obtained for three successive readings. The refractive index obtained for the saturated solutions is found in Table IX and the solubility as determined by estrapolation is found in Table X
I36
