ELECTROMOTIVE FORCE OF AQUEOUS HYDROGEN CHLORIDE A N D GLYCEROL
April, 1953
463
served values of the advancing and receding angles becomes sufficiently pronounced to cause the liquid on smooth surfaces were used to approximate the to spread down the grooves. The curves for the observed receding angles also respective stable angles in making calculations for both systems. The calculated values for both lie between the curves for the bevel and groove systhe bevel and groove systems and the observed ap- tems. A study of these curves indicates that the parent contact angle values for rough surfaces have recession of liquids on rough paraffin surfaces is been plotted in Figs. 2-4, as abscissas while the controlled by the movement of liquid through the corresponding observed contact angles on the grooves, though, as the receding contact angle obsmooth paraffin surface have been plotted as ordi- served for a smooth surface decreases, the effect of the liquid in moving across the beveled faces benates. As predicted, the curves for the observed appar- comes more important. One then can conclude that in this research the ent contact angles lie intermediate between the curvw for the values calculated for the bevel system observed values for the apparent advancing and reand for the groove system. I n general, the ob- ceding contact angles on the roughened surfaces served advancing contact angles approach the val- differ from those obtained for smooth surfaces as a ues for the bevel system, but as the advancing con- result of the altered physical structure of the surtact angles on the smooth surfaces decrease, they face. The resultant observed contact angle is deare increasingly influenced by the effect of the liq- termined by the orientation of the liquid surface in uid in the grooves. For methanol on a groove sys- making the stable contact angle with the solid surtem, the calculated apparent contact angle a be- face along the entire periphery. When advancing, comes zero when becomes greater than 42'. For the movement of the liquid drop across the surface surfaces where = 45") therefore, the decrease in is controlled predominantly by the movement of the observed apparent methanol advancing con- liquid over the pyramid faces. When receding, tact angle below the value obtained on surfaces the movement of the liquid drop is controlled preruled a t = 30' can be accounted for by this pro- dominantly by the movement of the periphery in nounced groove effect. This also, then, accounts the grooves. The observed hysteresis on paraffin for the decrease in hysteresis for methanol as the surfaces is then the result of the effect of the physiangle 4 is increased. For paraffin surfaces where cal nature of the surface on the observed contact 4 = 60' the effect of the methanol in the grooves angle.
+
+
+
ELECTROMOTIVE FORCE STUDIES I N AQUEOUS SOLUTIONS OF HYDROCHLORIC ACID AND GLYCEROL FROM 0 TO 40' BY SAMUEL B. KNIGHT,H. D. CROCKFORD AND F. W. JAMES C d r i b u t i o n from the Venable Chemical Laboratory of the University of North Carolina, Chapel Hill,N . C. Received October 90,1962
Electromotive force measurements on cells of the type Hg I HCI ( m ) ,glycerol ( y ) I AgC1, Ag were carried out in acid concentrations up to approximately 0.12 m and in 10 and 30% by weight of glycerol. Measurements were made a t 5 " intervals from 0 to 40". Standard cell potentials have been calculated for the cells a t the various temperatures. The mean activity coefficients Gf HCl can be calculated from the Debye-Huckel expression using a value of 6.6 A. for the ion-size parameter. The calculated values agree closely with the experimental values.
The work reported on in this paper is a continuation of the studies being carried on in this Laboratoiy on the effect of mixed solvents on the thermodynamic properties of hydrochloric acid solutions. In this work electromotive force measurements were made on the cell H,/HCl ( m ) ,glycerol (x),H20 (g)IAgCI-Ag
from 0 to 40' a t 5' intervals in solutions containing 10 and 30% by weight of glycerol and with acid concentrations ranging up to approximately 0.12 m. The activity coefficients of the acid in the various solutions a t 25' and the standard cell potentials a t the various temperature have been calculated from the data obtained. A study has also been made of the ion size parameter at the various temperatures. This supplements the work of Harned and Nestler,l who studied the same cell in Soy0glycerol, (1) H. S. Harned and F. H. AI. Nestler, J . Am. Chem. Soc., 68, 665 (1946).
with acid concentrations up to approximately 0.1 m, and a t 5' intervals from 0 to 90'; and Lucasse,p who studied this cell in 3.06 and 21.2y0 glycerol, with acid concentrations up to 4 m but only at a temperature of 25'.
Experimental The method of purification of chemicals other than glycerol, the preparation of the electrodes and the experimental procedures, were essentially the same as those of Williams, et a1.3 Glycerol .-Reagent grade glycerol was used without further purification, since purification procedures did not seem to improve the quality of the material used and in some cases seemed to induce some slight decomposition. The composition of the glycerol solutions was checked by density measurements using the tables of Bosart and Sn~ddy.~ (2) W. W. Lucasse, ibid., 48, 627 (1926). (8) J. P. Williams, 8. B. Knight and H. D. Crockford. ibid., 7 2 , 1277 (1950). (4) L. W. Bosart and A. 0. Snoddy, Ind. Eng. C h e m . , 19, 50G f 1927).
SAMUEL B. KNIGHT,H. D. CROCKFORD AND F. W. JAMES
464
Vol. 57
TABLE I m
50
00
-Temperature15'
100
20
250
30 '
359
40'
0.012981 .026730 .050330 .061193 .074614 .094906 .11989
10% Glycerol 0 . 4 4 0 3 5 ~ 0 . 4 4 1 7 7 ~ 0 . 4 4 3 0 0 ~ 0 . 4 4 4 0 3 ~ 0 . 4 4 4 8 7 ~ 0 . 4 4 5 6 1 ~ 0 . 4 4 6 1 6 ~ 0.4466I v .40811 .40893 .40963 .41009 .41038 .41036 .41033 .41018 .38020 .38039 .38016 .37986 .38035 .37978 ,37928 .37868 ,37041 ,37114 .37134 .37134 ,37118 .37085 .36978 36903 .36244 ,36250 ,36235 .36202 .36149 .36090 .35921 ,36010 .35161 .35146 .35114 .35063 ,34999 ,34925 .34833 .34706 .34102 .34165 .3405I .33981 ,3390 1 .33803 .a3603 .33565
0.44694 .41000 ,37797 ,36806 ,35822 ,34601 ,33426
0.022661 .035571 .049297 .064536 .078708 .099021
0.40262 .38237 .36818 .35620 .34742 .33728
30% Glycerol 0.40464 0.40501 ,38343 .38346 .36845 ,36821 35587 .35543 .34661 .a4602 .33595 .33516
0.40500 ,38203 .36567 .35226 .34229 .33081
e
0.40343 .38388 .36843 .35626 .34731 .33700
0.40412 ,38324 .36852 .35613 .34705 .33656
I
Vapor Pressures .-Vapor pressures were obtained from large graphs plotted from the data of Carr, Townsend and Badger.6 Densities.-All densities were determined in a pycnometer of about 15-ml. capacity. Dielectric Constants.-The dielectric constants of the two solutions were calculated a t the various temperatures from the following equations of Akerlof .E log D (10% glycerol) = 1.8896 - 0.00207(1 20) log D (30% glycerol) = 1.8560 0.00211(t 20) The electromotive force measurements, corrected to 1 atm. of hydrogen, are averages of a t least three cells usually agreeing within 1 0 . 0 5 mv. The time necessary for equilibrium at 25', at which temperature the first determination was always made, was approximately four hours. Approximately one hour was required for a new equilibrium value when the cell temperature was changed. Some of the readings were made by starting the cells at 25O, dropping to 0" by 5' steps, raising the temperature back to 25O, then
-
-
i 25
05
0.40526 .38328 .36$82 .35487 .34528 .33436
0.40528 .38300 .36723 .35418 .34435 ' ,33333
0.40522 ,38260 .36652 .35334 .34345 .33214
making readings a t 30, 35 and 40°, and then dropping back to 25' for a check on the electromotive force a t this temperature. Other measurements were made by the same procedure except that the cell temperature was raised from 25 to 40' in 5' steps, then dro ped back to 25', then :hanged to 0" at 5" intervals, and [nally raised back to 25 The three readings at 25' agreed within d0.05 mv. All electromotive force measurements are expressed in International Volts.
.
Calculations and Results The standard electrode potentials were determined by use of the function E' defined by the equation E' = E
+ 2K log m - 12+K Ad Bd /dC/ c 2K log (1 + O.O02md~,,) = Emo + f(m)
(1)
in which E' is the apparent molal potential, E is the observed electromotive force corrected to 1 atm. of hydrogen, m is the molality of the acid, A and B are the Debye-Huckel constants, d is the ion size parameter in A., C is the concentration in moles per liter, M x yis the mean molecular weight of the solvent, and K equals 2.3026RT/F. Table I gives the observed electromotive force values for the various molalities a t the various temperatures. Figure 1 shows the manner in which the observed electromotive force changes with temperature for three typical concentrations for the 10% solution. The same typical curves were found for the 30% solutions. The density values were found to fit an equation of the type d=a+bm
04420 O D 0 0 I3
ea M~lalityof HCI
O M l O 03730
oa
na
\l
Curva A, 0.012981 m Curve 8, 8 , 0.050332 O0503Mm Curve C, 0.119089 m
45
0
a
ID
I I3
20
25
SU
U
40
Temperalure, .C.
Fig.
1.-Eexp.
vs. temperature, solvent: 10 weight per cent.
glycerol.
( 5 ) A. R. Carr, R. E. Townsend and W. L. Badger, Ind. Eng. Chem., 17, 643 (1925). ( 6 ) G. Akerlof, J . Am. Chem. Suc., 64, 4128 (1932).
The values of a and b for the two concentrations of glycerol a t the various temperatures, together with the values of the constants in equation (1) are given in Table 11. This table also includes the values of the standard cell potentials a t the various temperatures. The standard cell potentials in Table I1 were determined by plotting the function E' in equation (1) versus the molality of the acid. Several values of the ion size parameter were tried for the various temperatures in order to determine the best value of d . The E' values obtained in this manner are not presented here as they can all be calculated
.
ELECTROMOTIVE FORCE OF AQUEOUS HYDROGEN CHLORIDE AND GLYCEROL
April, 1953
TABLE VALUES OF
11
solutions and by Crockford and Sakhnovsky’ for
COKSTANTS A N D STANDARD CELLPOTENTIALS d-fructose solutions.
The standard cell potentials for the two glycerol concentrations were found to fit the equations
t,
A
D
OC.
B
EO
b
a
10% Glycerol 0 5 10 15 20
8 5 , 3 1 0.51294 83.29 .51738 81.34 .52185 79.42 .52708 77.55 .53225 75.74 ,53771 73.95 .54364 72.21 .55350 70.50 .44618 19.60
25
30 35 40 MI,
465
0.32945 .33040 .33134 ,33245 ,33353 .33469 .33590 ,33790 ,33847
1.0253 0.0188 0.23076 .22824 1.0250 ,0190 .22557 1.0243 ,0190 .22274 1.0234 ,0180 ,21970 1.0222 ,0180 ,21650 ,0184 1.0207 .21315 1.0192 ,0176 .20965 1.0173 .0180 ,20600 1.0151 .0194
EO, (10% glycerol) = 0.21650 - 0.000652(t EO, (30% glycerol) = 0.20221 O.O00668(t
-
- 25) - 0.0000033(t - 25)a - 25) - 0.0000034(1 - 25)*
The potentials calculated for the 10% solution agree within +0.05 mv. in all temperatures. For the 30% solutions the agreement was equally good except for one temperature with variation 0.06 mv.
30% Glycerol 79.10 77.22 75.34 73.55 71.78 70.05 68.38 66.73 65.13 23.81
0 5 10 15 20 25 30 35 40 Jfxy
0.57443 0.34211 ,57983 ,34321 ,58532 ,34426 ,59146 .34547 ,34661 ,59730 ,60431 .34793 ,61130 .34929 .61860 .35065 .I32634 ,35215
1.0786 0.0172 0.21684 ,21421 1.0773 .0170 .21141 1.0758 ,0188 .20861 1.0741 .0170 .20545 1,0722 .0172 ,20221 1.0702 .0172 ,19882 1 , 0 6 8 1 .0166 .I9521 1.0658 .0162 ,19140 1.0634 .0160
from the data given. However, the curves obtained for the various ion size parameters a t 25’ and for 10% glycerol are given in Fig. 2. The curves obtained for the other solutions were similar to those shown. It is seen that a value of 6.6 A. for the ion size parameter gives a curve that is parallel to the concentration axis up to a molality of approximately 0.07 m. The lowest value of the ion size parameter that gives a straight line ovzr the concentration range studied is about 5.5 A. No matter what ion size parameter is used the value of the standard cell potential can be considered as correct to k0.06 mv. It would appear from the curves shomn that the value of the ion size parameter is lgrger than in pure water solution. A value of 0.6 A. was found by Williams, et al.,s for glucose
Fig. 3.--Eom ws. 1/D,HCI-glycerol-water solutions, 25’.
The standard cell potentials for the two solutions a t 25’ are plotted versus 1/D in Fig. 3. This curve also includes the point for the 50% solution obTABLE I11 MEANACTIVITYCOEFFICIENTS OF HYDROCHLORIC ACIDIN GLYCEROGWATER MIXTURESAT 25” Molality
X - 0
X = 10%
X=30%
0.005 .01 * 02 .03 .04 .05
0,9285 .9048 .8755
0,928
0.912 .884 .853 .834 .820 .808 .798 .790 .783. .777 .772
.8304
.06
000
I
004
I
001
I
003
I
001
I
005
Y*I.lil”
I
006
1
OD7
I
008
I
009
I
010
I\c
OII
012
I
Of HCI,
Fig. 2.-E’ us. molality of HCI at 25’ using various values for ionic parameter (d); solvent, 10 weight per cent. glycerol.
.873 .854 ,840 ,828 .818 .809
.07 .08 -09
.IO
.903
,7964
,802 .796 .791
(7) H. D. Crockford and A. A. Sakhnovsky, J . Am. Chem. SOC., 73, 4177 (19.51).
MAXBENDER
466
tained by Harned and Nestler’ and the two points for the solutions studied by Lucasse.2 A consideration of the data of Lucasse leads us to the conclusion that the dielectric constants for the 21.2 and 3.06y0solutions should be 77.1 and 72.5 rather than 76.0 and 66.9 as used by Lucasse. The standard cell potential for the 21.2% solution has been recalculated to be 0.2084 v. The mean activity coefficients, h y , of hydrochloric acid in the two glycerol solutions a t 25’ were computed from the e.m.f. data by the equation log y* = (E”,
- E)/0.1183 - log 7n
(2)
The activity coefficients so calculated were plotted versus m on a large scale and the values a t rounded molalities determined. These are given in Table
VOl. 57
111together with the values for the acid in pure water as listed by Harned and Owen.8 The experimental activity coefficients can be reproduced almost exactly by the Debye equation log y* =
-
+ d B d / c - log (1 + 0.002nlnf,,) + C’C AdE
1
in which C’ is a constaht introduced too account for the “salting out” effect. Using 5.0 A. for the ion size parameter and C’ values of 0.137 and 0.147 for the 10 and 30% glycerol solutions the maximum variation of the activity coefficient from the esperimental value was found to be 0.003. (8) H. 9. Harned and B. B. Owen, “The Physical Chemistry of Electrolytic Solutions,” Reinhold Publ. Corp., New York, N. Y., 1943, p. 340.
THE MECHANISM BY WHICH ALUMINUM IONS ALTER THE ELECTROKINETICS OF THE ZINC SULFIDE-WATER INTERFACE’r2 B Y MAXB E N D E R 3 Department of Chemistry, New York Univereily, New York, N . Y . Received October 30. 1966
Data are presented to show the electrokinetics of sphalerite particles as a function of aluminum ion concentration in alkaline, distilled water and acidic media. The effectiveness of the aluminum in altering particle charge depends very much on the medium. At the isoelectric point, in distilled water, the system is highly sensitive to the addition of aluminum ions; whereas, in alkaline medium, the sensitivity is one thousand-fold less. Sensitivity is still less in acid medium. The magnitude of the negative to positive change in electric charge of the spha1erit)ein the presence of aluminum also depends on the medium. This is greatest in alkali and least in acid. Visible flocculation of the sphalerite at the solids concentration under consideration occurs only in alkaline medium and only a t the isoelectric aluminum chloride concentration. These results are most readily explained, not by the direct adsorption of aluminum ions, but by the consideration of aluminum in conjunction with hydroxyl ions a t the particle-aqueous medium interface.
Introduction The results to be described suggest amechanism for the adsorption and gathering of aluminum ions a t the interface between particle and suspending medium, wherein the zeta potential of the particles is determined. Normally, a suspension of zinc sulfide mineral (sphalerite) in distilled water is negative in charge. 4 ~ 5 Addition of sulfuric acid decreases this negativity so that the isoelectric point is practically reached, but the charge does not become positive even a t 0.1 M HzS04.4p6 Likewise, a high concentration of NaCl (1 N ) causes the zeta potential to be almost zero although not positive, and flocculation6 does not occur either with the acid or the salt (the particles being well under one micron in size and a t a concentration of 0.0125% by weight4). In direct contrast with the acid and common salt, aluminum chloride does reverse the sign of the (1) Presented at the National ACS Meeting, Atlantic City, September, 1952, as “The Effect of Aluminum Ions on the Electrokinetics (Flocculation) of Sphalerite Particles.“ (2) (a) The data cited in this paper are from M. Bender, Ph.D. Dissertation, New York University (1949); (b) see also ref. 4. (3) American Cyanamid Company, Calco Chemical Division, Bound Brook, N. J. (4) M. Bender and H. Mouquin, THISJOURNAL,56, 272 (1952). (5) A. M. Gaudin and S. C. Sun, A.I.M.E. Tech. Pub. No. 2005 (1946). (6) Flocculation (coagulation) is defined in all this work, as the grouping together of the majority of the “individual” particles of a suspension, which are mostly microscopic and submicroscopic in size, to become macroscopic in size.
sphalerite. Also it flocculates it under given conditions. The effectiveness of the aluminum in these actions is markedly dependent on whether the suspension is alkaline, neutral (distilled water), or acidic, extremely low concentrations being involved in the case of the distilled water. Experimental Part,icle charge measurements were made in a rectangular modified Nort,hrup-Kunitz cell. The suspensions, which contained 0.0125% by weight of sphalerite, were prepared from t8hemineral by grinding in a “Diamonite” mortar and pestle. Since most of the particles were less than 0.3 micron ( p ) in radius it was necessary t.o use dark field microscopy to follow them. The temperahre at which cataphoretic velocities (C.V.) were determined was that of the room, but the values obtained were corrected to 25” by multiplication by the ratios of the viscosities of water at t.he corresponding temperatures. Amount and sign of the particle C.V. was studied as a function of the aluminum concentrat,ion in three different media, namely, basic (0.001 N NaaCOa), distilled water and acidic (0.002N H&04)and Figs. 1; 2 and 3 are the respective plots. In the alkaline medlum the pH changes with aluminum concent,rat,ionand cataphoretic velocity as shown N AlCls X 10‘
pH
C.V.
1.00 3.00 3.60 3.75 3.99
9.5 8.5 7.9 7.9 7.8
-2.79 -1.04 -1.29 -0.30 -0.12
(7) Figure 1 published in ref. 4.
N AlCls x 104
4.00 4.25 4.80 10.00
PH
7.7 7.6 6.9 5.3
C.V.
+0.02 -0.06 4-2.31 $3.00
