1252
SISTER M. EVA HALASEY
PARTIAL MOLAL VOLUMES OF POTASSIUM HOFMEISTER SERIES'
SALTS OF THE
SISTER M. EVA HALASEY, O.S.B.1 Department of Chemistry, St. Louis University, St. Louis, Missouri
Received April 8 , 1041
Hofmeister (8) first observed that certain ions assumed a definite order in their effect upon the osmotic pressure of protein solutions and upon physiological reactions. Pauli (18) and Hofmeister (8) arranged the anion series in descending order, as follows: Sulfate, chloride, nitrate, bromide, iodide, sulfocyanate Spiro (23) showed that acids and alkalies had a more pronounced influenee than water upon the distension of gelatin and other colloids, and arranged the acids in descending order. More recent work (24) dealing with the effect of neutral salts upon the swelling, osmotic pressure, and viscosity of colloidal proteins has produced comprehensive cation and anion series, some of the anions being arranged in descending order as follows: Sulfate, tartrate, citrate, chloride, bromide, nitrate, iodide, sulfocyanate Anions of the neutral salts have power according to the lyotropic series to lower the freezing point and to change the viscosity and surface tension of water. Urban (24) investigated the action of electrolytes upon the specific heat of water a t temperatures ranging from IO0 to 4OoC. He demonstrated both a cation and an anion series in which the anions were active generally in the same order as in the Hofmeister series. The author undertook the measurement of the partial molal volumes of eight potassium salts of the Hofmeister series, hoping that the rate of change in volume with concentration might produce a well-defined series. The salts selected were the chloride, bromide, iodide, nitrate, sulfocyanate, sulfate, tartrate, and citrate. Direct volume measurements were made on solutions of ten different concentrations (0.005 to 0.5 molal) a t eleven different temperature intervals ranging from 5' to 30'C. MATERIALS
Conductivity water was prepared by redistilling ordinary distilled water in Pyrex glass from an alkaline permanganate solution. Before use in calibration of the dilatometers or in making up solutions, the water was 1 The material presented in this paper comprises a summary of the author's research a t St. Louis University. Doctor F. W. Laird suggested the problem and offered much valuable criticism. 2 Present address: Mount St. Scholastica College, Atchison, Kansas.
PARTIAL MOLAL VOLUMES OF SALTS
1253
freed from carbon dioxide by boiling. For short periods the water was stored in a large Pyrex flask lined with paraffin. The halide, nitrate, sulfate, and tartrate salts were recrystallized from the purified water. The potassium sulfocyanate was recrystallized from absolute alcohol. A citrate of analytical quality was used without further purification. The halides, nitrate, and sulfate were dried a t a temperature of 100°C. for a period of 48 hr. The remaining salts were dried for a longer period a t a temperature between 90" and 100°C. As a check upon the purity of the salts, their refractive indices were measured by a Bausch and Lomb dipping refractometer, and were compared with the values in the International Critical Tables. The refractive index of the sulfocyanate was slightly low; that of the citrate was high. As recrystallization did not improve their quality, the salts were used in the hope that the slight impurities present would not vitiate greatly their lyotropic effects. The refractive indices of the other salts checked with the values given in the tables. APPARATUS
Four dilatometers3 (figure l), each of about 60-ml. capacity, were made as follows: A capillary tube, calibrated with pure mercury under a travelling microscope, was sealed to a piece of glass tubing which in turn was sealed into a 50-ml. glass bulb. Identification marks were made with a diamond pencil a t the upper and lower ends of the capillary. One stopcock was sealed into the tubing just below the capillary and a second was sealed to the opposite end of the bulb. The stopcocks had been ground previously with fine emery in turpentine and finally with a mixture of turpentine and camphor. The dilatometers were calibrated a t each temperature with the conductivity water. Corrections in the volumes had to be made for the solutions held in the two stopcocks. The difference in the density with the correction was very little a t the higher concentrations; however, it was appreciable in the very dilute solutions. EXPERIMEXTAL PROCEDURE
All solutions were made up on the weight basis, the corresponding molal weight of salt being added to lo00 g. of water. The four dilatometers were filled with solutions just above the lower mark on the capillary, and the stopcocks were closed. Excess solution was removed from the glass tubing above the stopcocks. The glass tubing was then closed with rubber tubing containing a short piece of glass rod. The top of the capillary was covered with a short piece of rubber tubing closed with a pinch cock, which allowed adjustment of the pressure reguThe author is indebted t o Doctor F. W. Laird for the glass blowing.
1254
SISTER M. EVA HALASEY
larly, yet prevented evaporation. Each dilatometer was placed in a vertical position in a thermostat held constant to &O.O25"C. Low temperatures were attained by pumping a cold brine solution through the coils of the thermostat. The solutions were left in the bath until equilibrium was attained. The time was usually 30 to 45 min. After the meniscus remained constant for about 5 min., the height of the solution in each capillary was measured with a cathetometer capable of being read to
L
FIG.1. The dilatometer
The thermostat was then adjusted to a new temperature and the process was repeated. I n this manner readings from 5" to 30°C. were taken a t 2.5-degree intervals. Two runs had to be made to obtain the expansion over the whole temperature range,-the first from 5" to 20"C., and the second from 20" t o 30°C. At the end of each run, the dilatometers were taken from the thermostat, wiped dry, and allowed time to come to room temperature (30 to 45 min.), when they were tared and weighed on the analytical balance. Duplicate runs were made of each concentration. As a rule all the runs for one salt were made in the same dilatometer; however, 0.1 mm.
PARTIAL MOL.4L VOLUMES O F S.4LTS
1255
excellent checks were obtained 11-hen the same solutions were measured in different dilatometers. C.iLCULATI0KS
The specific volumes and the densities of the solutions were first calculated from the experimental data and subsequently the apparent molal volumes. The values of the apparent molal volume^ n-ere plotted graphically against the square roots of the molal concentrations, and the best straight line \vas drawn. I'tilizing Masson's (17) relationship
+ = a + bc"'
(1)
Tvhere 9 is the apparent molal volume and c is the concentration, the constants a and b were evaluated from the graph. From the equat,ion so obtained another simple linear equation x i s derived expressing the partial molal volume of the salts. When, in a constant weight of water (1000 g . ) , varying amounts of salts are dissolved, the number of moles of salt may be represented4 by n l and the number of moles of water by 112 or .55.51. I t follows that
nhpre V is the total volume of solution and 5 5 . 5 1 ~is~ the volume of pure water. In equation 1, c may be represented by m (molality) and vz is IiuInerically equal to nl. Substituting in equation 1 : $I = a
+ bm"'
(3)
Substituting in e'quation 2 :
Equating equations 3 and 4 and clearing fractions:
Y
=
+
5 5 . 5 1 ~ ~a m
+bd"
(5)
Differentiating equation 5 with respect to the number of moles of salt, the water being constant:
being the partial molal volume of the salt. Owing t o the length of this paper, the author has not included the denPities which might be expressed by Root's (21) equation. The density Lewis and Randall (1.5) represent moles of solvent by ni andmoles of solute by nl.
1256
SISTER SI. EVA HALASEY
of any solution may easily be determined from the apparent molal volumes as follows: Total weight of solution = density of solution Total volume of solution
TABLE 1
.
Values of constants i n equations 3 and 6 at 6' lo 30°C. TEMPERA-
P O T A M D Y BROMIDE
POTABLIIUY CELORIDZ
POTABLIIUM IODIDE
-
yam C.
5.0 7.5 10.0 12.5 15.0 17.5 20.0 22.5 25.0 27.5 30.0
5
23.45 23.70 24.10 24.38 24.71 25.05 25.42 25.82 26.25 26.65 28.98
3.040 2.920 2.800 2.70 2.612 2.544 2.500 2.465 2.432 2.200 2.064
a
b
a
b
30.40 31.00 31.65 32.17 32.65 33.00 33.37 33.65 33.89 34.10 34.30
2.500 2.375 2.263 2.165 2.070 1.55 1.863 1.800 1.746 1.697 1.663
41.75 42.35 42.97 43.52 44.00 44.40 44.80 45.15 G.48 45.78 46.08
2.573 2.18 1.875 1.40 1.650 1.30 1.70 1.414 1.369 1,332 1.260
-
POTAOBIUM NITBA'RI 5
33.50 34.50 35.03 35.50 36.00 36.46 37.07 37.42 37.77 38.16 38.45
b
3.780 3.538 3.310 3.100 2.940 2.790 2.640
2.520 2.408 2.300 2.200 -
TABLE 2 *Values of constants i n equations S and 6 at 6' to S O T . TEMPERA?RE
POTAOBDY IIULFOCYANATE
C.
b
5
5.0 7.5 10.0 12.5 15.0 17.5 20.0 22.5 25.0 27.5 30.0
39.97 40.60 41.48 42.03 42.66 43.28 43.77 44.23 44.70 45.13 45.53
POTAOBIVY CITBATE
POTAMIUY BUVATTE
a
-
b
b
4
10.45 10.098 9.857 9.715 9.574 9.476 9.376 9.304
'OTAOBIUY T A S T R A m
5
b
*
~
32.42
11.553
,
112.3
11.723
7.636
81.33
6.717
83.20
6.067
84.20
I
9.164
80.47
+
5.444
__
Total weight of solution = molal weight of salt lo00 g. (water) Total volume of solution = +m volume of lo00 g. of water
+
Then
+
Molality weight of salt lo00 g. = density ~m volume of 1000 g. of water
+
1257
PARTIAL MOLAL VOLUMES OF SALTS
TABLE 3 Apparent and partial mold volumes of potassium nitrate
0.005 0.01 0.025 0.05 0.075 0.1 0.2 0.3 0.4 0.5
'1
1 ~
1
1 ~
9
33.77 33.88 34.10 34.34 34.53 34.69 35.19 35.57 35.89 36.17
33.90 34.07 34.40 34.76 35.05 35.29 36.03 36.61 37.09 37.51
Q
51
9
36.21 36.29 36.46
36.31 36.44 36.69
36.00
34.85 35.16 35.51
34.67 34.88 35.11
=>I-
__ 35.25 35.36 35.55 35.78 35.94 36.08 36.53 36.84 37.09 37.37 ___
31 9 --
il
35.72 35.81 35.99 36.19 36.35 36.48 36.89 37.20
35.38 35.53 35.81 36.14 36.39 36.60 37.25 37.75 38.17 38.54
35.83 35.96 36.24 36.54 36.77 36.97 37.58 38.05
m .__--
0.005 0.01 0.025 0.05 0.075 0.1 0.2 0.3 0.4 0.5
37.71 38.00 38.22 38.43
I
i
~
i
51
36.76
38.33 38.77 39.13 39.42
Q
37.25 37.33 37.49 37.66 37.79 37.90 38.25 38.51 38.74 38.96 __
9
37.35 37.46 37.68 37.95 38.15 38.32 38.84 39.24 39.57 39.87
AT
0.005 0.01 0.025 0.05 0.075 0.1 0.2 0.3 0.4 0.5
9
il
#
37.94 38.01 38.15 38.31 38.43 38.53 38.85 39.09 39.30 39.47
38.02 38.13 38.34 38.58 38.76 38.91 39.39 39.75 40.06 40.33
38.32 38.39 38.52 38.67 38.79 38.89 39.19 39.42 39.61 39.79
il
37.67 37.82 37.98 38.11
m
_~
I
37.80 38.02 38.27 38.45
w'c.
4
38.40 38.51 38.71 38.93 39.10 39.25 39.70 40.05 40.34 40.60
38.61 38.67 38.80 38.94 39.05 39.15 39.43 39.65 39.84 40.01
38.68 38.78 38.97 39.19 39.35 39.49 39.93 40.27 40.54 40.78
DATA AND CALCULATIONS
The constants a and b in the general equations 3 and 6 have been evaluated and may be found in tables 1 and 2. In table 3 the apparent and partial molal volumes of potassium nitrate are expressed. Table 4 con-
1258
SISTER M. kVA HALASEY
tains a comparison of the partial molal volumes of the 1ialides.obtained by the author with the values of Gronwall and La Mer (7) a t 25°C. Table 5 furnishcs a comparison of the densities of potassium chloride obtained by the author and by other workers (4, 13). Table 6 comprises equations of partial molal volumes a t 25°C. Table 7 shows actual values TABLE 4 Partzal molal volumes of potasszum halides at 25°C. I POTABSIUM CHLORIDE
POTASSIUZ1 BRO\lIDE
m a
0 01
~
~ Author ~
27 06
26 61
~R
1
&
1
~
~
34 49
Author ~
34 15
P o m a a i L \ 1 IODIDE
~and Gronu La &ell
45 85
1
4uthor
45 69
TABLE 5 Densities of potassium chloride DEABITY OF TEMPERATURE
0.01 MOLAL KC1
Bremner,
I
Utterback
1
Thompson. and
,
1 .Author
'
1 .000488 1.0002169 0.999611 0.998714 0.997564
lo00500 1 000230 0 999623 0 998722 0 997555
I KCI
I1
"C.
5 10 15 20 25
I
1
I
,
I
Jones and Rs,
I -~ ntolairty
0 0 0 0
005 01 5 1
' 1
~
0 2
1
DENGITY AT
05
0 997306 0 997540 0.9999440 1 001787 1 @I6456 1.020275
25'C.
Author
0.997314 0.997555 0.999457 1.001810 1.006455 1.020025
of partial molal volumes at infinite dilution obtained by several investigators (5, 6, 7 , 11, 17, 19, 22, 25, 2 7 ; also this paper). DISCUSSION O F R E S U L T S
Since the partial molal volumes of all the salts are expressed by the same general linear equation, inspection of the b values a t a given temperature
1259
PhRTIAL MOLAL VOLCMES OF SALTS
will reveal for the eight salts the order of magnitude in the rate of change with concentration. In view of table G, the series may be arranged in descending order as follows: Citrate, sulfate, sulfocyanate, tartrate, chloride, nitrate, bromide, iodide The values of i'ersus ml'* for several salts are plotted graphically in figure 2 . Variations in the slope of the graphs for the halides and the nitrate are very slight. -kcording t o Redlich and Rosenftld (20), a t great dilution all should have the same qlope. All equations for potassium nitrate TABLE 6 Equatzons f o r partzal molal Lolumes of potassaum salts at 85°C. Chloride.. . Dl = 26.25 Bromide, 8, = 33.89 Iodide, . . , , D1 = 45.48 S i t r a t e . . , c1 = 37.77 ,
I
,
I
+ 3.648m'!?
(7)
+ 2.619m':2 (8) + 2.053m112 (9) + 3.612m'/* (10)
Sulfocy- i anate., . = , Sulfate . . 8 ) = Tartrate. V I = i Citrate . ,I =
41.70 32.42 83.20 112.30
.I
+ 13.875m"2 (11) + 17.329m1l2(12)
+
9.100m*/2 (13)
+ 17.584m1'2 (14)
T.ABLE 7 Values of partial molal ziolumes at infinite dilution
Chloride.. . . . . . . . . . Bromide.. . . . . . . . . I Iodide.. . . . . . . , . . . . j Sulfate.. . . . , , . . . Citrate Chloride 1 Nitrate Tartrate ,
25 25 25 25 25 20 15 20
'27.0: 6.52 26.3 16 2326.74 34.4( 3.7333.7 133.97 i45.8: 5 3635 27 , 32 28'33 70
' I
I
1
!
26.251 1 33.891 45.48 ' 32.421 1 112 301 110 00 '26.68125 42 1 36 0035 75' 81 331 79 78 ~
,
~
are presented graphically in figure 3, which is typical also of the other salts. The slopes of the sulfate and the citrate are very nearly the same, while that of the sulfocyanate is intermediate in value when compared with the citrate and tartrate. Several factors may be a t nork to cause differences in rate of change in the various volumes with concentration. namely, (a) a specific ionic effect upon the water equilibrium; ( b ) the size of the ions; (c) hydration of the ions There is little knowledge a t piesent regarding the effect of various ions upon the polymerization or depolymerization of water.
1260
SISTER Ma EVA HALASEY
Judging&from the molccular volumes of the halides and the nitrate in the solid state, the order of change in solution is reversed a t 25°C. I n other words, among these four salts the smallest ion, the chloride, shows the greatest rate of change in solution. The sulfocyanate, which in its
FIG.2. Plot of d versus m1'1 a t 25°C. Curve 1, potasaium chloride; curve 2, potassium bromide; curve 3, potassium sulfate; curve 4, potassium nitrate; curve 5 , potassium iodide; curve 6, potassium sulfocyanate.
solid state is comparable in size to the other univalent ions, is so much out of proportion in solution that its size cannot be the sole factor in the rate of change in volume with concentration. At temperatures ot,her than 25°C. the nitrate precedes the chloride in the series. Several experimenters (10, 12, 16, 17) are agreed that the nitrate is not
PARTIAL .MOLAL VOLUMES OF SALTS
1261
hydrated in solution. At low concentrations (0.1 M ) Baborovsky, Yiktorin, and Wagner (1) have calculated a high degree of hydration for the potassium halides, the iodide showing the greatest and the chloride the least hydration. At higher concentrations, 0.5 M to 1 M , the determinations of Bourion (2, 3) and of Hun (9) show a lesser degree and the reverse order of hydration. Kruyt, Robinson, and Conmar (14),in testing the “salting-out” effect among salts of the Hofmeister series, found a greal
m 1/2 FIG.3. Plot’ofd versus
ml’l
for potassium nitrate at 5-30°C.
difference between the sulfate and the sulfocyanate. This difference they attributed to considerable hydration of the sulfate ion and little or no hydration of the sulfocyanate ion. I n the present series the two ions are close together. Supposing no conflicting forces, the molecular size of the salts containing the divalent and trivalent ions would account for a greater rate in volume change with concentration. Electrostriction is a possible governing factor
1262
SISTER
M. EVA HALASEY
in placing the tartrate below the sulfate, despite the greater size of the ion. Similarly, the greater size of the ion in the case of the citrate may be so overbalanced by the hydration effect that the rate of change in volume is nearly the same as that of the sulfate. With the exception of the sulfocyanate, and in some instances the nitrate, there is a similarity between the order of the ions in the present series and in that of other experiments (18, 23, 24, 26). Rluch of the data in the literature on apparent and partial molal volumes are based on volume concentration. The author’s data are all calculated on the weight or molal basis. Still, comparisons are in fair agreement. Table 4 illustrates the differences in the partial molal volumes of the halide salts a t 25’C. as calculated for corresponding molalities from Gronwall and Laller’s ( 7 ) equations. The agreement from 0.1 nz to 0.5 m is good in each case, though greater differences are found at the loll-er concentrations. Cantelo and Phifer’s (5) straight-line equation, derived from the data of Gronwall and La Mer ( 7 ) for potassium chloride (0.2713 to 2.2926 m ) , is practically the same as that of the present work. Table 7 reveals, among investigators, close numerical values of partial molal volumes a t infinite dilution. The author’s value for the chloride is lower in general than the values found by others. The partial molal volumes of the citrate and the tartrate in this investigation are higher than those obtained by calculation from density data in the International Critica 1 Tables (11). SUMMARY
‘
1. Equations of apparent and partial molal volumes have been presented for five potassium salts a t ten concentrations (0.005-0.5 molal) and a t eleven temperature intervals (between 5” and 30°C.). Like equations have been formulated for three other potassium salts a t a few temperatures only. All the numerical values for potassium nitrate have been tabulated. 2. The eight potassium salts have been arranged in series according to the magnitude of their change in volume with change in concentration of the solution. 3. Several comparisons have been made between the values of the present work and those of other investigations. REFERENCES (1) B.ABOROVSXY, VIKTORIX, A N D WAGSER:Collection Czechoslov. Chem. Commun. 4, 200 (1932). (2) BOURIOX ASD HUN:Compt. rend. 198, 1921 (1934). (3) BOURXON . ~ F D ROUYER: Compt. rend. 196, 1111 (1933). (a) BREMNER, THOMPSOS, A N D UTTERBACK: J. .h. Chem. SOC. 60, 26115 (1938). (5) CANTELO A K D PHIFER:J. Am. Chem. Soc. 66, 1333 (1933). (6) GEFFCXEN:Z. physik. Chem. A166, 1 (1931).
SILICIC ACID GELS.
XI11
1263
(7) GROXWALL A X D L AMER: J. Phys. Cliem. 31, 393 (1027). (8) HOFMEISTER: Arch. exptl. Path. Pharmnkol. 24, 1, 248 (1889); 26, 1 (1889): 27, 395 (1800): 28, 210 (1891). (9) H r s : Compt. rend. 202, 1779 (1936j. (10) ISGHARI: J. Chem. Soc. 1930, 5-12. (11) Internntionnl Critical Tables. 1-01,111, p. 91. lIcGmw-Hill Book Company, Inc., S e w York (1928). (12) JABLCZYSSKI: Roczniki Chrm. 13, 167 (1933). (13) .JOSER ASD R.AY:J . Am. Chern. SOC. 69, I87 (1937). SD C o s v \ r r ~ I'c~rliandcl. : .4kad. Tt'ctcnscliappcn Amstcrntuiirkundt~36, 812 (10263. (15) LEWISASD I t . t s D . A L L : ThernrodyiLamics nntl f h c I,'rte E n t r g T i!f C'hcmical Sube t n n c t s , p . 3 5 . NcGraiv-Hill Book ('ompnny. I n c . , l e i v l-orl; (1023). (16) M . m r w n . r JIHRSTORFER, ASD ZEPTER: Z.anorg. allgem. Cl~cni.141, 45 (1924). (17) MASSOS:Phil. Mag. 171 8, 218 (1029). (IS) PAVLI: Beitr. Chem. Physiol. Path. 3, 225 (1902). (19) PEARCE .ASD ECKBTROM: .J. -1m. Cheni. Soc. 69,2689 (1937). (20) REDLICH ASD ROSESFELD: Z . physik. Chem. A166, 65 (1031). (21) ROOT:J. :hi. Chem. SOC.66, 850 (1933). (22) SCOTT: J. Phys. Chem. 36, 2315 (1931). (23) SPIRO:Eeitr. Chem. Physiol. Path. 6, 276 (1904). (24) URB.AX: ,J. Phys. Chem. 36, 1108 (1932). (25) \VADE: J. Chcm. Soc. 76, 254 (1809). (26) KEITZASD STOXM:Ber. 61B, 1114 (1925). (27) WIRTH: J. Am. Chem. SOC.69, 2549 (1937).
STUDIES O S SILICIC ACID GELS. XI11 SOME EXAMPLES O F RE-GELATION CHARLES B. HURD
AND
LOUIS W. THOMPSOS, JR.'
Department of Chemzstry, Cnaon College, Scheneclady, S e w York Recezved October 1 7 , lQ@ INTRODUCTIOh-
Several years ago, while studying the p H of silicic acid gels, Hurd and Griffeth (6) noted that a silicic acid gel which had been beaten into very fine particles in a n equal volume of distilled mater apparently possessed the property of re-gelation. The finely divided, milky material settled, and this settled material became mushy and finally firm. TVe thought then that the phenomenon was related to the behavior of a silicic acid gel misture, which, if stirred just bel'ore it sets, will still set to form a firm gel. Certain gels are known, consisting of fine, intermeshed crystals, which 1
Present address: E. I. du Pont de Xemours & Company, Waynesboro, Virginia.
