6%
.
M. H.
Ihereactions are summarized, for comparison, in Table VIII.
TABLE I RATE OF ADSORPTION OF COBALTBY HYDROUS FERRIC OXIDE gram atom; Constant factors: Total Co, 2.80 X gram atom; pH 8.0; ovolume, 31.4 0.1 ml.; Fe, 2 X "&I, 0.034 N ; temperature, 15 ; equilibrium quantit'y gram atom. of cobalt in solution, 2.0 X
+
Adsorption period, hr.
Cobalt adsorbed,
Cobalt adsorbed, gram atoms
0.53 1.0 2.0 5.3 7.5 10.0 14.0 25.0 35.1 40.0
69.6 70.1 77.6 81.2 83.7 84.8 89.2 92.8 93.0 92.2
1.95 1.99 2.17 2.27 2.34 2.37 2.50 2.60 2.60 2.58
%
x
109
Cobalt in solution less equilibrium quantity in solution, gram a t o m X lo9
0.65 .61 .43 .33 .26 .23 .10
TABLE I11 RATE OF ADSORPTION OF COBALTBY
690
~YDROIJS
FERRIC
OXIDE
Coiist.ant factors: Total Co, 2.80 X 10-9 gram atom; Fe, 1 X 10-5 grain atom; pH 8.0; volume, 32.5 f 0.8 ml.; N HICI, 0.034 N; temperature 31.7'; equilibrium quantity of cobalt in solution, 3.0 X 10-10 gram atom. Adsorption period, hr.
Cobalt adsorbed,
%
Cobalt adsorbed, gram atoms x 109
1.2 4.2 6.3 8.5 11.0 19.5 30.0 60.2 72 94 236
76.8 80.2 82.3 83.5 85.6 87.7 89.4 88.8 88.8 88.9 88.8
2.15 2.25 2.31 2.34 2.40 2.46 2.51 2.49 2.49 2.49 2.49
Cobalt in solution less equilibrium quantity in solution, gram atom X 109
0.35 .25 .10 .16 .10 .04
TABLE IV COBALTBY -.:DROUS FERRIC OXIDE Constant factors: Total Co, 2.80 X gram atom; Fe, 0.5 X 10-6 gram atom; pH 8.0; ovolume, 30.3 =k 0.1 ml.; YHdCI, 0.034 N ; temperature, 36.3 ; equilibrium quantity of cobalt in solution, 4.0 X gram atom. RATE OF
OF
-JSORPTION
Adsorption period, hr.,
Cobalt adsorbed,
%
Cobalt adsorbed, gram atoms x 109
1.B 5.9 10.1 12 14 25 31 37 50 60 73 78 135
60.8 62.4 68.4 69.2 72.8 78.8 79.8 81.4 83.2 83.2 82.2 82.7 81.0
1.70 1.75 1.92 1.04 2.04 2.21 2.23 2.28 2.33 2.33 2.30 2.31 2.20
Cobalt in solut,inn less equilibriuli-qua,ntity in solutlon, gram atoms X 109
0.61 .56 .30 .37 .27 .10 .08 .03
TABLE V
RATE OF ADSORPTIONOF COBALTBY HYDROUS FERRIC OXIDE TABLE I1 gram atom; Constant factors: Total Co, 2.80 X RATE OF ADSORPTIONOF COBALTBY HYDROUSFERRIC Fe, 2 X 10-5 gram atom; pH 8; .volume, 30.23 k 0.1 ml.; n",CI, 0.100 N; temperature, 36.3'; equilibrium quantity OXIDE of rohalt i n solution, 2.2 X gram atom. Constant factors: Total Co, 2.80 X 10-9 gram atom; Fe, Cobalt in solution 2 X 10-6 gram atom; pH 8.0; volume, 31.7 f 0.34 ml.; Cobalt less equilibrium NH,CI, 0.031 N; temperature 30' ; equilibrium quantity Adsorption Cobalt adsorbed, quantity in period, adsorbed, gram atoms solution, gram of cobalt in solution, 1.8 X gram atom.
1.5 6.0 7.1 10.1 13.2 20.3 35.1 37.0
76.6 84.6 85.2 88.1 90.3 93.2 93.5 02.9
2.15 2.37 2.39 2.47 2.53 2.61 2.62 2.60
0.47 .25 .23 .I5 .09
hr.
%
2 4 6 8 11 14 17 24 40 48 60
78.6 82.5 84.4 84.9 86.6 88.6 89.3 91.0 92.0 92.2 02.2
x
109
2.20 2.31 2.36 2.38 2.43 2.48 2.50 2.55 2.58 2.58 2.58
atom X 109
0.38 .27 .22 .20 .16 .10 .08 -03
M. H. I~URBATOV AND GWENDOLYN 13. WOOD
700
TABLE VI
TABLE VI1
RATE OF ADSORPTIONOF COBALTBY HYDROUS FERRIC RATE O F
ADSORPTION O F
OXIDE
Adsorption period, hr.
Cobalt adsorbed,
%
Cobalt adsorbed, giam atoms x 109
1 4 8 10 12 18 24 40 48 60
26.5 29.9 33.4 33.8 34.8 36.6 37.4 38.3 38.3 38.2
0.74 .84 .94 .05 .97 1.02 1.05 1.07 1.07 1.07
Cobalt in solution less eouilibriuin quahtity in solution. gram atom X 109
Cobalt adsorbed,
%
Cobalt adsorbed, gram atoms x 109
0.3 0.6 1.25 2 4 5 8 10 14 16 20 25 30 35 40 52 GO 80
65.0 G9.8 73.9 76.4 81.9 84.3 86.2 87.1 88.1 80.2 90.6 00.6 92.0 00.2 92.0 91.7 90.6 90.8
4.16 4.47 4.76 4.80 5.24 5.40 5.52 5.58 5.64 5.71 5.80 5.80 5.88 5.77 5.88 6.87 5.80 ,5.81
#
TIME INHOURS
,Fig. 1. I
8
RATES 5 A N D 6
32-
0
0
2
I
i
l
4
6
8
l
l
l
l
l
l
l
10 12 14 16 TIME IN HOURS
18
20
22
24
Fig. 2.
l
26
Cobalt in solution less equilibrium uantity in so?ution, gram atom X 10’
1.66 1.35 1.06 0.93 .58 .42 .30 .24 .I8 .ll
TABLE VI11 SUMMARY OF RATESTUDIES Total Table cobalt, no. or gram rate atoms no. X 109
7
m a
HYDROUS FERRIC
Adsorption peripd, hr.
1 2 3 4 5 6
5
BY
Constant factors: Total Co, 6.40 X gram atom; Fe, 2 X 10-6 gram atom; pH 8.0; volume, 31.6 f 2 ml.; NH,CI, 0.0345 N; temperature, 20’; equilibrium quantity of cobalt in solution, 5.8 X 1O-O gram a t o m
0.33 .23 .13 12 .10 .05 -02
I n order to determine the rates of adsorption, the time in hours was plotted against the log of the difference between gram atoms of cobalt in solution a t time, t , and gram atoms of cobalt in solution a t equilibrium. The amount of cobalt in solution a t equilibrium was subtracted since it represents the “zero” quantity or concentration in solution for this equilibrium reaction. The quantities of cobalt in solution are directly proportional to the concentrations since the rates were studied at constant volume. The first six rates (Fig. 1 and 2) proved t o be first order with respect to cobalt. In all of these the ratio of total cobalt to iron as hydrous oxide was not more than 2.8. X 10-o gram atom of cobalt to 5 X 10-6 gram atom of iron in about thirty milliliters of solution. That is, the conditions were in each instance, those of a part of an isotherm in which Henry’s law applies, or the quantity of cobalt adsorbed a t equilibrium is proportional to the concentration of cobalt.
5-
COBALT
OXIDE
Constant factors: Total Co, 2.80 X gram atom; Fe, 2 X 10-6grrtm atom; pH 7; volume, 29.88 =!= 0.05 ml.; “&I, 0.034 N; temperature, 36.3 ; equilibrium quantity of cobalt in solution, 1.73 X 10-0 gram atom.
2
Vol. 5G
’
2.8 2.8 2.8 2.8 2.8 2.8 64.0
Adsorbent quantity, gram atoms F e X 105
P €1
2.0 2.0 1, 0 0.5 2.0 2.0 2.0
8 8 8 8 8 7 8
.
NHiCl nor- Temp.’, V mality “ C . hr.
0.034 .034 .034 .031 .lo0 .034 .034
15 30 32 36 36 36 20
* ~ Rate
5 5 5.4 7.7 6 6 5.8
constant
0.14 -14 .13 .09
.ll .ll .12
Rates 1 and 2 obtained at 15 and 30’, respectively, show no difference in rate resulting from this temperature change. The half-life found in each rate study was five hours. Rates 2, 3 and 4 show the results of decreasing the amount of adsorbent from 2 to 1 to 0.5 X 10-6 gram atom of iron as hydrous oxide. The half’-lives obtained were 5, 5.4 and 7.7 hours. That is, less adsorbent resulted in a slower rate of adsorption. Comparison of rates 2 and 6 (half-lives 5 and 6 hours) shows the effect of change in pH. Rate 2 was obtained a t pH 8 and rate 6 a t pH 7. The rate of adsorption at higher hydroxide ion concentration was greater. Rate 5 was carried out in the presence of 0.100 A! ammonium chloride while rate 2 had only 0.034 N salt with other conditions comparable, The half lives obtained were 6 and 5 hours. That is, the higher salt concentration resulted in a lower rate. I t is of some interest that rates 5 and 6 have the same halflives, within experimental error, and that both of these are slower than rate 2 with which they are compared above. I n other words, a threefold increase in salt concentration (from 0.034 to 0.1 N ) was experimentally equivalent, in its effect on rate of adsorption, to a decrease in hydroxyl ion concentration from 10-6 to 10-7. This emphasizes the known sensitivity of this adsorption system to rather large changes in hydroxyl ion (tenfold in this case) a t low concentration levels and also points out the influence of smaller changes (three-fold in this case) of chloride concentration at much higher concentration levels ( 3 X 10-9 to 10-1).
Juiic, 1952
CRITICAL
MICELLEC O N C E N T R A T I O N S
Rate 7 was obtained with 6, X 10-8 gram atom of cobalt and 2 X 10-6 gram atom of iron as hydrous oxide. This rate was not first order but gave a curve when plotted as t,he other rates were. The experimental curve is shown in Fig. 3 along with the curve obtained by subtraction. The latter curve indicates an initial first order rate having a constant of 0.69 and a half-life of one hour. The half-life of the subtracted curve is 5.8 hours. The experimental conditions for rate 7 were thosc for a point on a n isotherm above the region of cobalt ion to adsorbent ratios in which Henry's law holds. Under thcsc conditions, the cobalt adsorbed a t equilibrium is not directly proportional to its concentration in solution: thc unreacted adsorbent is not in large excess but is significantly reduced by the cobalt adsorbed. It seems then that the initial rapid first order ratc is due to the adsorbent, the cobalt ion being in excess. After 5.4 X 10-8 gram atom of cobalt was gram atom in solution, the rate adsorbed, leaving 1 X bccamc expcrimentally first order with respect to cobalt and its half-life was 5.8 hours. Refercncc to Table VI11 shows that this half-life lics bctwcen thosc obtained for 1 and for 0.5 X 10-6 gram atom of iron as hydrous oxide when tho total cobalt uscd was 2.8 X 10-9 gram atom.
BY B U B B L E P R E S S U R E h'fETHO1)
701
m
It is a pleasure to aclinowledge the continued interest of Professor Ed. Mack, Jr., in thiswork. This research \vas supported in part from funds granted
CltI'l'ICRL MICELLE CONCENTRATIONS BY -1 BUBBLE PliESSUltE METHOD BY A . S.BROWN, R. U. ROBINSON, E. H. SIROIS,H. G. THIBAULT, FV. MCNEILLAND A. TOFIAS JIcGregory Hall of Chemislry, Colgale University, Hamilton, N . Y . Received J u l y $0, 1961
The bubblc pressure method of measuring surface tensions has been modified by using it kinetically. The air pressurc needed to maintain a stream of bubbles in a surfactant solution is a complex function of concentration and bubble rate. Plots of bubble pressure against concentration have been obtained for the commercial cationic and anionic materials laurylpyridinium chloride, Santomerse #3 and Tergitol TMN-050. The major discont#inuitieswere confirmed as critical micelle concentrations by conductancc measurements for the L.P.C. and Santomerse. This techni ue shows considerable dctail in thc pressure-concentration plots, possible rcasons for this being considered. The utility of %e method for solutions containing clectrolytes has been examined briefly for Saiitonicrse in 1.84% sulfuric acid.
This Laboratory has recently been interested in mometer tubing or 22 gagc B & D hypodcrmic needles, the tip being immersed to a known dept,h of 3 to 10 mm. in the the behavior of surfactant systems, particularly solution. The needle hub was attached horizontally to glass under non-equilibrium conditions which resemble tubing by De Khotinsky (medjiim) cement, as shown sepapractical applications of such agents. This study rately on an enlarged scale 111 Fig. l . Air pressure was was initiated in the belief that the pressure required measured on a simple manorncter such as Cenco #73840 against, atmospheric pressure, the open end being either free t o eject a stream of air bubbles through a given (for major adjustments) or restricted by a capillary to miniorifice submerged in surfactant solutions would be mize pulses during readings. Air was supplied at a rate consuch a function of both the concentration of the trolled either by a sensitive long-arm screw clamp on a supsolution and the rate of bubble formation that the ply from a Kipp generator opcratcd with water or preferably, R shown in Fig. 1, by water displacement of the air in a 1dependence of pressure upon concentration would aor 2-pintswide-mouth vacuum bottle. Tho Iat)t>crtcchniquc change markedly a t thc critical micelle coiicentra- pcrniitt,cd inscrtion of a manifold of rcstrictivc capillary tion a t some critical bubble rate. During the first tubes abovc the vacuum bottle and in tho water line from experimental work it was noted that a number of thc constant head supply permitting a rapid shift from onc water dropping rate to another wit.h a minimum of delicatc reproducible irregularities appeared i n the plots adjustment. The constant head water supply was a Matof pressure against concentration and it was be- viakl unit wit,h t,he lower end of the water leg, the dropping lieved that these might correspond to the forma- tip, adjusted vertically to compensate for changes in the tion of different micelles. To test this interpreta- manomet,ric pressure. Rate of water flow could be checked by counting drops. Glass tubing was connected with rubtion it was decided to measure electrical conduct- ber tubing, and scrcw clamps, markcd "X" in Fig. 1, served ances paralleling the bubble pressure studies since as valves. sharp discontinuities in the conductance plots Conductance measurements were made at 1000 cycles with clearly indicate the sudden formation of new student-grade boxed slide-wires opcrated near mid-point, decade resistance boxes and Wagner grounds. species. The correlation between breaks in the two adequate Calls generally comprised Pyrex flasks with small dependent types of plots is encouraging. bulbs containing the Pt hlacked electrodes connected to the
Experimental The bubble pressure apparatus i s depicted in Fig. 1. The bubblc-forming orifice comprised standard tubing, ther-
bridge circuit with mercury fillcd side arms. Water-bath t,hermostats maintained a temperature of 25.00 f 0.02'. (1)
BI. hlatviak, Chemist-Andust, 40, 24 (1951).
