02
E. D. FISHER AND C. H . SORUM
time is shown to be the sum of two intervals, each dependent on the concentration of silica and of hydrogen ion. The bearing of this experiment upon the fibrillar condensation theory of silicic acid gel structure has been discussed. REFERENCES (1) HURD,C. B.: Chem. Rev. 22, 403 (1938). (2) HURD,C. B., FREDERICK, K. J., AND HAYNES,C. R . : J. Phys. Chem. 42,s(1938). R. L.: J. Phys. Chem. 39, 1155 (1935). (3) HURD,C. B.,AND GRIFFETR, (4) HURD,C. B., AND LETTERON, H . A.: J. Phys. Chem. 38, 604 (1932). C. L., AND MILLER, P. S.:J. Phys. Chem. 38,663 (1934). (5) HURD,C. B.,RAYMOND, (6) JORDIS,E . : Z. anorg. Chem. 44, 200 (1905). (7) TREADWELL, W.D., AND K ~ N I CW.: , Helv. Chim. Acta 16, 54 (1933).
T H E INFLUENCE OF SOL CONCENTRATION ON FLOCCULATION VALUES E. D. FISHER
AND
c . H. SORUM
Department of Chemistry, University of Wisconsin, Madison, Wisconsin Received March 24, lgS9 INTRODUCTION
The influence of sol concentration on the flocculation values of pure ferric oxide and chromium hydroxide hydrosols has been previously reported (3, 5 ) . With these pure sols the flocculation values decreased for monovalent ions, remained constant for divalent ions, and decreased for trivalent and tetravalent ions as the sols were diluted. This behavior conformed to the flocculation rule formulated by Burton and Bishop (1). When these pure sols were made impure by adding small amounts of stabilizing electrolytes, the flocculation values for all ions decreased as the sols were diluted. In this paper a more detailed study of the behavior of chromium hydroxide sols will be presented, as well as observations on other typical systems. Changes in flocculation values when the sols were dilited with alcohol are also included. CHROMIUM HYDROXIDE
Table 1 shows the effect of the addition of chromium chloride on the flocculation values of a pure chromium hydroxide sol a t various dilutions. The monovalent coagulating ions chosen are widely separated in the Hofmeister series; two polyvalent ions are also included. The sol was prepared by precipitating the hydroxide from a chromium chloride solution
63
FLOCCULATION VALUES FOR SOLS
TABLE 1 Effect of the addition of chromium chloride on the flocculation values o f a chromium hydrozide sol SOL CONCENTRATION
I
100%
80%
40%
1.3 3.4
2.0 3.8 7.0 9.5 14.0 16.0
2.4 4.1 7.0 9.0 13.5 14.5
NaCl
0.0 0.1 0.2 0.3 0.4 0.5
11 .o 16.0 20.0
1.7 3.7 7.0 10.0 15.0 18.0
NaCsH801
0.0 0.1 0.2 0.3 0.4 0.5
1.1 2.0 3.7 4.9 5.5 6.0
1.3 2.2 3.8 5.0 4.5 5.5
1.5 2.0 3.6 4.6 4.0 5.0
1.6 1.5 3.3 4.2 3.5 4.0
NaI
0.0 0.1 0.2 0.3 0.4 0.5
1.2 3.6 10.0 15.0 23.0 27.0
1.6 3.9 10.0 14.0 22.0 26.0
2.2 4.1 10.0 13.8 21.0 22.0
3.0 4.3 10.0 13.5 19.0 20.0
NaSCN
0.0 0.1 0.2 0.3 0.4 0.5
1.0 1.9 4.0 5.5 8.0 10.0
1.4 2.1 4.2 5.0 7.5 9.5
1.6 2.2 4.0 5.0 7.0 9.0
1.8 2.3 3.8 4.5 6.0 8.0
NaL301
0.0 0.1 0.2 0.3 0.4 0.5
0.06 0.08 0.14 0.18 0.19 0.23
0.06 0.07 0.12 0.16 0.16 0.20
0.06 0.07 0.10 0.13 0.14 0.15
0.06 0.06 0.09 0.11 0.12 0.12
0.040
0.030 0.045 0.065 0.085 0.085 0.110
0.025 0.035
0.0 0.1 0.2 0.3 0.4 0.5
8.0
0.050 0.080
0.110 0.125 0.140
0.055
0.070 0.075 0.090
0.020
0.025 0.045 0.050 0.060 0.060
by means of ammonia in a manner previously described (3). In the final purified state it contained 0.940 g. of chromium per liter. The original
64
E. D. FISHER AND
C. H. SORVM
sol is referred to as 100 per cent, and the lower percentages are in terms of the original concentration. Unless otherwise stated, all dilutions were obtained by adding water. The flocculation values of the pure so1 for the various coagulating ions again have shown that a pure chromium hydroxide sol follows the rule of Burton and Bishop when coagulated by ions of varying valences. When a sufficient amount of chromium chloride was added the flocculation values of all ions were higher, and those of the monovalent coagulating ions decreased as the sol was diluted. This behavior of the impure sol is contrary to that predicted by the Burton-Bishop rule. As the sols were made more impure by the addition of chromium chloride, the flocculation values for all ions showed a more distinct decrease with sol dilution. TABLE 2 Changes i n the flocculation values of sodium chloride when a chromium hydroxide sol is diluted with liquids DILUTINO AGENT
90% __
Water. . . . . . . . . . . . . . . . . . . . . .
SOL CONCEWPRATION
0.4
80Yo _ .
0.5 0.35 0.35 0.40 0.40 0.40 0.30 0.40 0.40
70%
__ 0.6 0.40 0.35 0.35 0.35 0.10 0.10 0.50 0.45
eo% 0.7 0.40 0.30 0.25 0.30 0.10 0.05 0.45
50% ~
0.8 0.40 0.25 0.15 0.30 0.08 0.001 0.30 0.20 0.15
__ 40%
30%
_ .
~
0.9 0.40 0.20 0.15 0.20 0.06
1.4 0.40 0.20 0.15 0.15 0.05
20% 1.8 0.45 0.20 0.10 0.05 0.05
0.10 0.05 0.01 0.20 0.20 0.20 __ __ __
The changes in the flocculation values of sodium chloride when A pure chromium hydroxide sol was diluted with absolute ethyl alcohol and similar liquids are shown in table 2. The original sol contained 0.825 g. of chromium per liter and had a flocculation value of 0.25 millimole of sodium chloride per liter. The sol showed a distinct increase in flocculation values when dilutions were made with water. As the dilutions were made with an increasing amount of alcohol the extent of increase diminished, and finally the flocculation values showed a decrease when a sufficient amount of alcohol was added. The results with methyl alcohol and acetone were similar to those exhibited with ethyl alcohol. In all instances the first diluting portions seemed to increase the sol stability toward sodium chloride, but as the amount of alcohol increased the flocculation values passed through a maximum and then decreased. Table 3 shows the effect of the addition of stabilizing electrolyte on this maximum flocculation value. The sol
65
FLOCCULATION VALUES FOR SOLS
used contained 0.631 g. of chromium per liter. A 60 per cent solution of ethyl alcohol in xater was used as the diluting agent. With the addition of chromium chloride the observed maximum decreased and soon disappeared, as shown by table 3. The changes observed when a pure chromium hydroxide sol is diluted with methyl and ethyl alcohols and acetone may be attributed to the dehydrating nature of the diluting liquids, since a pure sol quite definitely owes a major portion of its stability to hydration. The first dilution with these liquids is similar to dilution with water, since the flocculation values for monovalent ions increased. But with increasing dilution sensitization and dehydration became more acute and the flocculation values showed a decrease. When chromium chloride was added to a hydrated sol a large part of the sol stability was due to ion adsorption. When this is the case, dilution nitli nlcohol and other liqiiids becomes more similar to dilutions with water. TABLE 3 .
Efecl of the a d d i f i o n of stabilizing electrolyte on the maximum jocculalion value SOL CONCENTRATION
MILLIMOLES OF CrClr PER LITER
0.0 0.1 0.2 0.3
0.50 1.8 3.9 5.6
805
7OcO
0.65 1.8 2.9 4.6
0.60 1.7 2.6 4.3
50%
0.40 l.G 2.3 4.0
0.30 1.4 2.1 3.7
1
405
0.15 1.3 1 .n 3.3
ARSENIC TRISULFIDE
That the flocculation values for monovalent ions for an arscnic trisulfidc increase as the sol is diluted has long been known. This work shows how the addition of stabilizing electrolyte impurity changes the ordinary behavior with dilution. The sol was prepared by bubbling hydrogen sulfide through a saturated solution of arsenious oxide (4). The resultant sol was dialyzed in collodion bags for 24 hr. a t 50°C. In the final purified state it contained 1.18 g. of arsenic per liter. Table 4 shows the flocculation values with water and 95 per cent ethyl alcohol as the diluting agents. When the dilutions were made with alcohol the flocculation values for potassium chloride increased more than when the dilutions were made with water. A possible reason for this can be found in an ordinary rule of adsorption, which states that adsorption in solution is largely dependent upon the surface tension of the solvent. The addition of alcohol lowered the surface tension of the liquid phase; consequently adsorption was lessened and the presence of a larger amount of coagulating electrolyte was necessary for flocculation. 501
66
E. D. FISHER AND C. H. SORUM
Table 5 shows the flocculation values for potassium chloride when stabilizing electrolyte was added. It is evident that as the sol was made impure with stabilizing electrolyte the flocculation values became higher and the increase with dilution was much less. Larger amounts of sodium sulfide were not added, as its solvent action tended to destroy the colloidal nature of the sol. TABLE 4 Flocculation tlalzke for arsenic trisulfide sol with water and alcohol as diluents
Dilutions with water KCI . . . . . . . . . . . . . . . 78. BaClr. . . . . . . . . . . . . 1 0 . 6 CrCla... . . . . . . . . . . . 0.025
~
84. 0.6
90.
1 0 . 6
0.023
0.020
1
~
78. 0.6 0.025
1
II
90. 0.8 0.023
95. 0.8
~
0.020
98.
1
0.6 0,015
105. 0.8 0.018
1
130. 0.7 0.015
Dilutions with alcohol (95 per cent) KCl . . . . . . . . . . . . . . . BaCll . . . . . . . . . . . . . CrC1,. . . . . . . . . . . . . .
I
94. 0.6 0.017
TABLE 5 Flocculation values for potassium chloride i n presence of stabilizing PlectroEyte
____
SOL CONCENTRATION BTABILIZINO ELECTROLYTE
100%
1
80%
1
1
40%
1
~
1 millimole of NaSS per liter 2.5 millimoles of NalS per liter.. Sol saturated with HB
148
150
MANGANESE DIOXIDE
The sol was prepared by the reduction of permanganate by ammonia (2). In the final purified state it contained 0.320 g. of manganese dioxide pcr liter. Flocculation values are shown in table 6. Table 6 readily shows that the Burton-Bishop rule applies to the flocculation of manganese dioxide if the sols are made sufficiently pure by dialysis. When dilutions were made with alcohol some flocculation values first increased, then decreased with dilution,-behavior characteristic of a highly hydrated sol. This sol exhibited an “irregular series” with the polyvalent coagulating ions. Between the ranges of concentration shown for the flocculation values the sol was completely coagulated; at either
FLOCdULATION
67
VALUES FOR SOLS
end it was stable. The lower limit represents the flocculation values for a negative sol, and thc upper limit was the point a t which the sol had adsorbed a sufficient amount of positive ions to become a positivc sol. TABLE 6 Flocculation values for manganese dioxide sol
1
Sol dialyzed for 24 hr. at 90°C. Dilutions with water
NaC1. . . . . . . . 10.0 LiCl . . . . . . . . . 12.0 BaC12.. . . . . . 0.15 CrCla. . . . . . . . 0.12-0.06 .41Cla. . . . . . . .i 0.13-0.07 Th(NOa),. 0.05-0.03
,i
...I
10.0 11.0 0.15 0.09 -0.05 0.10 -0.06 0.045-0.025
,
9.0 10.5 0.15 0.08 -0.04 0.08 -0.05 0.03M.020
8.5 9.0 0.15 0.05 -0.03 0.06 -0.04 0.020-0.015
8.0
7.0 0.15 0.03 -0.02 0.03 -0.02 0.015-0.010
Sol dialyzed for 72 hr. at 90°C. Dilutions with water NaCl. . . . . . . . LiCl.. . . . . . . . KCl.. ....... BaC11. . . . . . . . CrC18. . . . . . . . Th(N0a)r. . . .
.I.I
1.0
1.1
1.9 0.06
NaC1.. . . . . . . 1.0 LiCl . . . . . . . . 1.6 KCI.. ...... 0.8 BaCIz. . . . . . . . 0.06 CrCla . . . . . . . . 0.065-0.015 Th(N0j)c.. . . 0.018-0.008
1.25 1.65 0.6 0.04 0.040-0.015 0.014-0.008
1.3 2.2 0.65 0.06
1.1 1.5 0.45 0.03 0.025-O.013 0.009-0.005
2.4
0.1 0.008
FERRIC OXIDE
‘l’hc fcrric oxide sol has been previously shown to follow the BurtonBishop rulc (5). This work was for the purpose of following changes in flocculation values when dilutions were made with ethyl alcohol. The sol was prepared and purified according to the method described by Sorum (6). In the final purified state it contained 1.708 g. of iron per liter. Table 7 shows flocculation values when dilutions were made with 95 per cent ethyl alcohol. Here again it seems probable that the decreasing stability with dilution is caused by the dehydrating action of the diluting alcohol. A stannic oxide sol was prepared by peptizing the precipitated hydroxide with ammonia, and was dialyzed for 2 days a t room temperature. In the
68
E. D. FISHER AND C. H. SORUM
final purified state it contained 2.88 g. of stannic oxide per liter. Table 8 shows flocculation values. Table 9 shows the results obtained with an aluminum hydroxide sol prepared by washing the precipitated hydroxide until it was peptized.
BOL CONCENTBATION BALTB
NaCl . . . . . . . . . . . . . KaCrHsO,. . . . . . . . . KaSCN. . . . . . . . . . . KCl. . . . . . . . . . . . . . LiCl . . . . . . . . . . . . . .
100%
80%
60%
10.5 4 .O 6.5 10.0 10.5
8.5 3.7 5.0 8.5 8.5
7.8 3.3
;:: ~
I ~
8.0
'
20%
6.5 2.8 3.7 6.5 7.5
1
5.5 2.0 3.0 5.5 7.0
4%
I
2%
40%
TABLE 8
I
SALT8
Flocculation values for stannic oxide sol a o L CONOENTUTION
100%
I
80%
1
60%
I
Dilutions with water NaC1. . . . . . . . . . . . . LiCl, . . . . . . . . . . . . . KC1. . . . . . . . . . . . . . BaC12. . . . . . . . . . . . . AlCls. . . . . . . . . . . .
.I
1
NaCl. . . . . . . . . . . . . LiCl.,. . . . . . . . . . . . KCl. . . . . . . . . . . . . .
1.0 1.o 0.75 0.04 0.009
0.7 0.7
0.6
::::
0.65 0.04 0.015
~
0.012
1
0.70 0.04 0.010
Dilutions with alcohol 0.70
0.60 0.65
0.60
0.60 0.60
1
0.55 0.55 0.50
~
0.M) 0.45 0.40
1
1.0 1.2 0.80 0.04 0.007
0.50 0.40 0.30
0.01 g. of NHa per liter; dilutions with water
XaC1.. . . . . . . . . . . . LiCl . . . . . . . . . . . . . .
!
5.0 5.5
~
4.0 5.0
~
3.2 4.5
I
2.5 4.0
1
2.0 3.8
Sols of titanium oxide and thorium hydroxide were prepared and purified fiy dialysis. Attempts to purify the sols to a high degree failed, as they coagulated in the dialyzer. With these sols the flocculation values for all ions decreased as the sol was diluted. However, the extent of decrease for the monovalent ions was noticeably diminished as the sols were dialyzed to higher degrees of purity.
60
FLOCCULATION VALUES FOR SOLS DIBCU8BION
The results have shown that with pure sols flocculation values increased for monovalent ions, remained about the same for divalent ions, and decreased with polyvalent ions as the sols were diluted. When the sols were made impure with stabilizing electrolyte, flocculation values for all electrolytes decreased. These results indicate that the applicability of the Burton-Bishop rule is determined by the purity of the sol. One of the possible factors contributing to the increased stability of diluted systems is the increased adsorption of the stabilizing ion of thc coagulating electrolyte with dilution ( 7 ) . When relatively large amounts of stabilizing electrolyte are already present it may prevent any great T.\RT,E 9 Floccitlalion iialues Jor an al~uninunih ~ d r o x i d esol
_.
. .
~
. . . . .
_
_
~
_
_
_
.
-
-
......
SOL CONCENTRATION BALTB
la070
1
SO:%
Dilutions with water NaCl.. . . . . . . . . , , . . , . , . . NaC2HaOz... . , , . . , . , . . NaSSO,. . . , , . , . . . . . . . . . KsFe(CN)o. , , , . . . . , . . , .
I
.I
32.0 8.0
29.0 7.0
,
I
' ~
. .
W0',
34.0 8.5 0.m 0.01
I
4OCb
.-
'
38.0 9.0 0.09 0.003
~
____________.
Dilutions with alcohol _____--____ vaC1.. . . . . . , . . . . . . . . . . . . B.O 21.0
.I
I
12.0
4.0
~
Undialyzed sol; dilutions with water NaCl
l
175
1
170
160
1
~
155
adsorption of ions of adde'd electrolyte. Hence the above-mentioned factor in increasing sol stability with dilution may not function. When hydration was a factor in sol stability, dilution with dehydrating agents naturally resulted in a decrease in flocculation values. This dehydrating effect more than balanced any stabilizing effects of dilution, as shown in tables 2, 3, and 6, where the flocculation values first increased but then decreased as further amounts of alcohol were added. SUMMARY
The applicability of the Burton-Bishop rule to hydrosols of chromium hydroxide, ferric oxide, arsenic trisulfide, manganese dioxide, stannic oxide, aluminum hydroxide, titanium oxide, and thorium hydroxide seems to be a function of the purity of the sol. Highly purified sols followed the
70
ELMER C. LARSEN AND JAMES H. W?LLTON
rule; sols containing relatively large amounts of stabilizing electrolyte did not. REFERENCES ( 1 ) BURTON AND BISHOP: J. Phys. Chem. 24, 701 (1920). (2) CUY,E. J.: J . Phys. Chem. 26,415 (1921). J. Phys. Chem. 39, 283 (1935). (3) FISHERAND SORUW: (1) FREUNDLICH AND SATHANSON: Kolloid-Z. 28, 258 (1921). (5) JUDDAND SORUM: J. Am. Chem. Soc. 62,2598 (1930). J. Am. Chem. See. 60, 1263 (1928). (6) SORUM: (7) WEISER:Hydrous O d e s . The McCraw-Hill Rook Company, Inc., Piew York
(1926).
ACTIVATED CARBON AS A CATALYST I N CERTAIX OXIDATION-REDUCTION REACTIONS' ELMER C. LARSEN
AND
JAMES H . WALTON
Department o j Chemistru, Universzty o/ Wisconsin, Madison, Wisconsin Received June 90, 1959
I. THEDECOMPOSITION OF HYDROGEN PEROXIDE Lemoine (17) in 1907 first reported that carbon is an effective catalyst for the decomposition of hydrogen peroxide solutions. I n 1923 Firth and Watson (5)found that heating ordinary sugar carbon in uucuo increases its activity greatly, but that after the reaction has proceeded for about 10 hr. the catalyst becomes ineffective. They also found (6) that the rate of decomposition is proportional to the quantity of catalyst used. It has since been observed (15) that heating in. an atmosphere of moist oxygen results in a still more active carbon. King (11) obtained a carbon of maximum activity on activating sugar carbon at OOOOC. and a product of minimum activity a t 45OoC. Hc found thc catalyst to bccomc incffcctive after the reaction had continued for about 90 min. Hc attributed thc dccay in activity to a chemical reaction bctwwn the pcroxidc and the surface oxide of the carbon. It is the purpose of this investigation to develop a technique for obtaining samples of activated carbon whose catalytic properties can be reproduced, and to use this carbon to obtain more accurate data on the factors affecting the rate of decomposition of hydrogen peroxide. Special emphasis is given to the decay of catalytic activity. In part I1 of this paper 1 This investigation was financed by a grant from the Research Committee of thr University of Wisconsin, Dean E . B. Fred, Chairman.
