tion 1, AECD-3647, U. 5. At. Energy
(17) Lai\p
R. W., “Reference Electrodes, ,D.J. G. Ives, G. J. Janz, eds., Academic Press, New York, 1961. (18) Liu, C. H., Johnson, K. E:, Laitinen, H. A., “Molten Salt Chemistry,” M. Blander, ed., Interscience, New York,
1964. (19) Long, G., U. S. At. Energy Comm. RezL ORNG3789. 72 (1965). (20) ‘Maddox, W. L:, Fisher, D. J., Ibid., ORNL-3060, 4 (1960). (21) Manning, D. L., J. Electroanal. Chem. 6, 227 (1963). (22) Ibid., 7, 302 (1964). (23) Manning, D. L., Dale,. J. M.,
Mamantov, G., “Voltammetry inMolten Fluorides,” Proceedings of the Third International Congress of Polarography, Southampton, 1964 (in press).
&;’R. S., Shain, I., ANAL. CHEM.36, 706 (1964). (29) Palei, P. N., ed., “Anal tical Chemistry of Uranium,” Danier Davey and Co., New York, 1963. (30) Pisaini, S., Agace, L., Con. Science 5 . 193 (1965). (31 j Pizsini, S.; Morlotti, R., Electrochim. Acta 10, 1033 (1965). (32) Pizsini, S., Sternheim, G., Barbi, G. B., Ibid., 8 , 227 (1963). (33) “Reactor Handbook,” Vol. 3, Sec-
Comm. (1955). (34) Reinmuth, W. H., ANAL.CHEM.32, 1514 (1960). (35) Saller, H. A., Rough, F. A., U. S. At. Energy Comm. Rept. BMI-1000 I,1-(15.5 - - - ,).. (36) Senderoff, S., Mellors, G. W., Reinhart, W. J., J. Electrochem. SOC.112, ,w (1965). (37) SeInderoff, S.,Mellors, G. W., Zbid.. 113, 66 (1966). (38) Shaffer, J. H., et. al., U. S. At. Energy Comm. Rept. ORNL-3789, 99 (1965). (39) Stromatt, R. W., J. Electrochem. SOC.110, 1277 (1963).
---
~
RECEIVED for review May 16, 1966. Accepted August 8, 1966.
PotentiaI-Time Cu rves of T ha I I ium, Lead, Cadmium, and Bismuth at Thin Mercury Film Electrodes FREDERICK L. MARSH’ and STANLEY BRUCKENSTEIN University of Minnesota, School o f Chemistry, Minneapolis, Minn.
55455
Concentrated metal amalgams may be deposited as a 4000-A. layer upon a rotating platinum electrode by simultaneously depositing mercury and metal from a nitric acid solution of mercurous (or mercuric) and metal ion. The potential-time curve obtained by chemical stripping with mercurous (or mercuric) nitrate can be predicted within experimental error. A potential-time expression is given, allowing for the changes in activity coefficients of mercury and the metal in amalgams, the latter being the most important correction.
that M is oxidized from the amalgam into a solution a t a constant rate according to
R
where C o A and Co, are the surface concentrations of metal in the amalgam, M A m . i , and Mn+, respectively, at the amalgam-solution interface; and f ’ ~ and fo. are the corresponding activity coefficients. aoas is the activity of the mercury at the interface. The a p proximations which are ordinarily made in polarography-Le., that a’sp is constant and independent of C’A, and f o A and j o A = 1-cannot be made for all amalgams deposited at the MCRPE. Such amalgams may be quite concentrated. They reached 7 mole % in the work reported below for thallium, and it wm necessary to use experimentally determined values of ~ O and A
current-voltage curves have been derived (5, 23) and supporting data presented (25) for a linear voltage scan oxidation at a thin film mercury electrode. Cadmium ion was deposited into the mercury film on a nickel electrode and anodically stripped. However, no quantitative treatment has yet been given for the oxidation of a metal from a thin film amalgam under conditions of constant flux. This work is a continuation of the study of the preparation, properties, and applications of the continuously deposited, mercurycoated, rotating platinum electrode (MCRPE) (1). Relations are derived which describe the experimental potential-time curves obtained during the chemical stripping of metal amalgam films 4000 A. thick by mercurous and mercuric ions. ECENTLY,
THEORETICAL
Consider a MCRPE which contains a metal, AT, uniformly distributed through the amalgam phase. Assume 1498
ANALYTICAL CHEMISTRY
MA^^^ -* Hg
+ M n ++
E
=
EO.hin+/.+iAmoi
and
(1)
under such conditions that a steady state surface concentration of M n + is established at the amalgam-solution interface. The reduction potential of the amalgam electrode under these conditions is given by
-
Jf“’ -I- ne -* M A m a l
Hg
[Hg(I)lz
+ 2e
Hg(I1)
+ 2e
+
2 Hg
or +
Hg
are mass transfer controlled. On cessation of electrolysis, the chemical reaction 2M~m.i
+
[Hg(I)I*
+
2Mn+
+ 2n Hg
(3a)
+ n Hg
(3b)
or
aoaa.
The conditions assumed for the model described correspond to the physical situation during the chemical stripping process which occurs at a MCRPE. The amalgam is formed by electrolyzing for T, seconds a solution of [Hg(I)]z or Hg(I1) containing a trace of Mn+ at a potential sufficiently negative that the reactions
2 M ~ m . i
f
HgW
+
2 M n f
occurs at the amalgam-solution interface, and the concentration of M A m o l decreases until it becomes zero. The potential of the MCRPE varies as a func5on of time as shown in Figure 1. In Figure 1, E , is the potential during the plating period, E, is the initial potential of the MCRPE a t the start of the chemical stripping process and t.hi is the time in seconds required to completely oxidize the metal from the amalgam. Under our experimental conditions T, = 300 seconds and t M , 2 2 seconds. The time required for diffusion of the metal from the platinum surface to the solution interface o 1 2 / 3 D ~(2) where D A is 8he diffusion coefficient of M A m o l and 1 = amalgam layer thickness. Typically, D A = 1.5 1 Present address, Gould-National Bat. teries, Inc., Research and Development Laboratory, 2630 University Avenue, S.E., Minneapolis, Minn.
becomes limited by the rate of transport of [Hg(I)]2 to the electrode surface. This rate is obtained from the limiting current, (il)1Bg(I,,,, for the reduction of [ H d I ) 12-
(7) Combining Equations 4, 5, 6, and 7 we obtain
C"
C [ 2T,R x + ' ]
=
(8)
by assuming, as before, that the instantaneow rate equals the average rate. Defining
e
=
co,/co
we have
c.0 = ec [2 T p R + 11 e Figure 1.
Plating and stripping potential-time curve of metal, M
X 10-5 crn.t/sec. and 1 = 4 x 10-6 cm., therefore this diffusion time is about 0.05 millisecond. This time is so short on the time scale of our experiment that the amount of metal remaining in the mercury after the stripping transition time would be negligibly small. Christensen and Anson (2) have obtained an expression for the concentration distribution across a thin layer electrode during a chronopotentiometric experiment. Under our experimental conditions their result predicts that we may consider the amalgam to have a uniform concentration across the thickness of the film. To evaluate the potential-time curve it is necessary to express the amalgam and solution surface concentrations in terms of T,, t M , the bulk concentration of M n + and [Hg(I)]z or Hg(I1). Given these surface concentrations, the necessary activity coefficients can be obtained from previously published thermodynamic data. (3, IS) Evaluation of C",. Let us assume that Mn+ may be in rapid reversible equilibrium with other soluble complexes containing M in the f n oxidation state, that the total bulk analytical concentration of M ( n ) species is C, and that the surface analytical concentration is C". Assuming a Nernst diffusion layer, the rate of reaction of M ( n ) species at the interface during the plating period, dNM(,)/dt, is proportional to the concentration difference between the bulk and the surface-Le.,
Steady state concentrations are established very rapidly a t a rotating
platinum electrode, therefore the instantaneous rate may be replaced by N M c n ) / Twhere p NM(,)is the number of moles of M ( n ) reduced during the plating period. If no plated M is lost by mechanical or chemical processes the amount of M found by oxidation from the amalgam, NM, is equal to -NM(,). When the reaction of metal ion is mass transfer controlled -N = M --=
TP
NM(n)
TP
kAw~
(5)
and k M can be evaluated if N M is known. The conventional evaluation of kM using a limiting current measurement was not possible in many of the cases we studied in the absence of [Hg(I)]z of Hg(I1). In their presence, the large current resulting from the [Hg(I)]t or Hg(I1) completely obscures the small limiting current of the metal ion. Also it is not generally possible to use comparable concentrations of M(n) and mercury ions, since hydrogen evolution occurs a t regions where M has precipitated from a saturated amalgam. Hence NM was calculated using Equation 19 of Reference ( I ) , and kM evaluated from Equation 5 using the calculated value of NM. According to Equation 3a, the rate of oxidation of M by [Hg(I)]z on cessation of plating is
Since steady state is rapidly attained, constant surface concentrations result. If Reaction 3a is rapid, C o ~ E ( r )bely comes zero, and the rate of Reaction 3s
(9)
If no equilibria involving Mn+ exist, = 1 . Otherwise 6 must be evaluated
from a knowledge of the various equilibria in solution (3). Evaluation of Surface Concentration in Amalgam. Mole fraction units are the most convenient concentration units to use in the mercury phase. The total number of moles of M deposited is obtained using Equation 19 in Reference (1). N H ~the , number of moles of mercury present on the MCRPE after all the M has been chemically oxidized was determined by electrochemically oxidizing the mercury a t constant current. If the chemical stripping process (Reaction 3s) has been occurring for t seconds, the mole fraction of M in the amalgam, X A , is
The numerator in Equation 10 corresponds t o the number of moles uf M unoxidized at time t , while the middle term in the denominator takes into account the changing number of moles of mercury in the film as a result of Reaction 3a. The mole fraction of mercury, XHg is given by Equation 1 I. XHp
=
1-
X A
(11)
Evaluation of Potential-Time Equation. I n terms of the mole fraction standard states in the mercury phase, and the molar concentration scale in the aqueous phase, the Nernst equntion analogous t o Equation 2 is
E
= Constant
- 0.0592 X n
VOL 38, NO. 1 1 , OCTOBER 1966
1499
where -y represents the activity coefficient on the mole fraction scale in the mercury phase. The constant in Equation 12 can be evaluated from E,, the potential of the cell (22).
M (solid)/Mn+/MA,,t (sat'd). I n terms of the standard potential of the metal ion/metal couple we have Constant =
E'U*+IM
+ E. +
YA*XA* log n YHg*XHg*
0.0592
~
X'A -= C'A
(13)
where the superscript, *, refers to saturated solutions. Combining Equations 9 through 13 we obtain
E = H + - 0*0592log n
where
H
=
because the conventional polarographic half wave potential uses a molar concentration scale in the mercury phase and we have converted to a mole fraction scale. Under normal polarographic conditions Y'A 1, boxg s 1. Also using 13.6 gram/cma as the density of mercury, da., and 200.6 as the atomic weight of mercury, in dilute solutions
J
+ +
(148)
E'M"+IM E, 0.0592 -log- ~ A * X A* e* j o a (14b) n YH~*XH~
at. wt. Hg.
x
= 1/67.8
(16)
dag
Hence, substituting Equations 16 and 14a into Equation 15, we have
H
=
Eiiz
- 0'0592 -log 67.8 + n
(:)"*
E 2 log n
(17)
and it is possible to compare the experimental values of H with reported experimental values of Ella using Equation 17. EXPERIMENTAL
Apparatus. The instrumentation and electrode construction have been previously described (2). The electrolysis cell was an all-glass unit with the main compartment separated from two side arms by fine fritted disks. A salt bridge to the reference saturated calomel electrode was introduced into one of the arms and an auxiliary platTerm H conBains standard potentials, inum electrode was placed in the thermodynamic quantities obtained other. The main compartment confrom a saturated amalgam and the structed from 50-mm. borosilicate tubing had two 15-mm. tubular openings terms e and f o e . Term I contains a t the top to accommodate the RPE quantities relative to the time of plating, and a coarse sintered glass dispersion solution concentration, and mass transtube for nitrogen bubbling. fer conditions. Term J contains all the Nitrogen. Linde prepurified nitroquantities dependent on the time of gen was further purified and then used stripping. Hence a plot of E us. log I / J to deoxygenate all solutions. The should be a straight line with a slope of nitrogen was passed from an active 0.0592/n and intercept H . copper column, through a gas washing An analogous result is obtained if bottle of distilled water for presaturation, and then through the fritted Hg(I1) is used instead of [Hg(I)]S. I n this case we define R = - d N ~ ~ , ~ n , / d t glass dispersion tube of the electrolysis cell. The active copper column was and terms H and I are unchanged m constructed and operated according to Equation 14a but term J is now J'. Meyer and Ronge (92). Water. Triply distilled water was used in the preparation of all solutions. The water was deionized by ion exchange resins before being disComparison with Polarographic tilled. The second distillation was Data. The expression for the polaromade from alkaline permanganate. Mercury. Berk and Co. triple graphic half wave potential is given distilled mercury was further treated by Kolthoff and Lingane (11). In to reduce the lead content to a terms of our notation, and taking into negligible level. Filtered air was account the use of a mole fraction conbubbled through a container of mercentration scale in the amalgam cury and 1.5M nitric acid solution for 24 hours. Afterward the mercury E1/z = E'M"+/M Ea was rinsed for several hours with several portions of distilled water and dried. Supporting Electrolytes. Concentrated Mallinckrodt AR nitric acid was mixed with an equal volume of water and was distilled. The second quarter fraction was collected. The conwhere D is the diffusion coefficient of the centration of this stock nitric acid quantity which appears as the subsolution was about 5 molar and it was script. The ratio X'A/C'A appears used to prepare the 0.1 molar supporting
+ +
1500
ANALYTICAL CHEMISTRY
electrolyte solutions. The third quarter fraction of the distillate was collected and was used to dissolve the purified mercury and other metals. The concentration of this fraction was about 12 molar. Standard Solutions. H g (NO&. A mercuric nitrate solution in 0.1M "01 was prepared by dissolving purified mercury in a three-fold excess of the purified, concentrated nitric acid, evaporating off the excess acid, and dissolving in nitric acid t o make a 0.0500M stock solution of mercury (11) in 0.1M nitric acid. Hgz(N03)Z. Mercurous nitrate stock solutions were prepared by mixing equal volumes of 0.1M nitric acid and a 0.0500M solution of mercury(I1) in 0.1M nitric acid over excess purified mercury, deaerating with the purified nitrogen, and shaking the mixture for 48 hours. This 0.025M mercurous solution in 0.1M nitric acid was removed from contact with the Hg metal and was stable. This solution contained an equilibrium concentration of Hg(I1) of 3.1 X lO-'M as determined by analysis. The analysis consisted of precipitation and filtration of Hg2C12 from excess KCl solution; measuring the limiting current of the remaining HgCI2, and comparing this limiting current with that of an HgClz standard solution when the potential of the MCRPE is -0.45 volt vs. SCE. TINOI. A standard solution of 0.0100M thallium(1) was prepared by dissolving weighed, dried Fisher c.P., thallium nitrate in 0.1M nitric acid. Pb(NO&. A standard solution of 0.100M lead(I1) was prepared by dissolving weighed Mallinckrodt AR lead pellets in an excess of purified, concentrated nitric acid; evaporating off the excess acid; and dissolving the residue in 0.1M nitric acid. Bi(NO&. A standard solution of 0.0100 molar bismuth(II1) was prepared by dissolving weighed Baker and Adamson granular bismuth metal in an excess of purified concentrated nitric acid; evaporating off the excess acid and dissolving the residue in 1.0 molar nitric acid. Cd(NO&. A stock solution of 0.05 molar cadmium(I1) was prepared by dissolving weighed Baker and Adamson cadmium nitrate tetrahydrate in 0.1M nitric acid. An aliquot of the stock solution was used to quantitatively determine cadmium according to the controlled potential electrolysis method of Lingane (15). The concentration of cadmium(I1) was 0.0496 molar. Pretreatment and Storage of RPE. I n all experiments the following pretreatment of the rotating platinum electrode (RPE) was performed immediately before the deposition of mercury. The electrode was introduced in a duplicate of the electrolysis cell filled with 50 ml. of deaerated 0.1 molar nitric acid. An anodic current of 1.00 ma. was passed through the electrode for 3 minutes, and then a cathodic current of 1.00 ma. was passed
0
1
-0.40
-0.50
E
Figure 2. Test of reversibility of TI(I)/TI (amalgam) according to Equation 14a 1
Curve A. 0 4.00 X 10-%4 TI(I), 2.50 X 10d4MHgn(NO&, least rquares slope = 0.060 volt, intercept = 0.527 volt Curve B. A 1 .OO X 1 O - W TI(I), 2.50 X 10 -'M Hgz(NO&, least squares rlope = 0.065 volt, intercept = 0.535 volt Curve C. 0 4.00 X 1 O%i TI(I), 5.00 X 1 O-'M Hg(NOJ2, least squares slope = 0.062 volt, Intercept = 0.533 volt Curve D. H 1 .OO X 10-'M TI(\), 5.00 X 1O-4M Hg(NO&., least squarer $\Ope = 0.064 volt, lntercepf = 0.537 volt Curve E. Curve A, assuming Y T I / Y H ~ = 1. Data points omitted for clarity. Slope = 0.0785
40
-
LOG l/J
0.0
Figure 3. Test of reversibility of Pb(ll)/Pb (amalgam) and Cd(ll)/Cd (amalgam) according to Equation 14a
-
-
for 3 minutes. Afterwards the electrode was moved to the plating cell and was ready for use after at least 5 minutes of additional deaeration. The RPE was stored in 0.1 molar nitric acid, and was carried through a pretreatment electrolysis cycle after the last run of the day. Precoating of RPE. T o obtain the most reliable stripping data it was necessary t o precoat the electrode with mercury before simultaneously depositing the metal and the mercury. This preplating step was done in solutions which contained both the mercury ion and the trace metal ion M ( n ) in 0.1M "01 by shorting the external leads of the R P E and the SCE together. The actual potential of RPE during mercury preplating differed a little from 0 volt us. SCE because of the cell resistance. For example, using an electrode with area = 0.14 em.* in a solution containing 2.50 X 10-4X Hg~(N03)gand 0.1M HNOa, E = +0.08 volt taking into account the total I R drop. In the experiments reported the electrode was precoated with mercury for 300 seconds, producing a mercury film of approximately 2000-A. thickness. Experimental Technique of Plating and Stripping. The chemical and electrochemical experiments were carried out using the apparatus as previously described (1). All solutions were prepared prior to use by diluting standard stock solutions with the 0.1M HN03. Fifty milliliters of plating solution were introduced into the main compartr ment of the electrolysis cell. The cell was thermostated at 25 f 0.1' C. for 10 minutes and the solution was bubbled with purified, water saturated,
1-0.70
I
-0.5
Curve A.
5.00 X 10% Pb(ll) and least squares slope = 0.032 volt, 1.00 X 10-M Cd(ll) and least squares slope = 0.033 volt
2.50 X 1 O-4M Hgz(NOa)r, volt, intercept = -0.431
A
2.50 X I O - % Hgz(NOa12, volt, intercept = 0.624
nitrogen. A freshly pretreated electrode was introduced in the main compartment and a plating and s t r i p ping experiment was carried out while nitrogen passed above the solution. The plating time, T,, used for the experiments reported below was 300 seconds. The mercury film thickness was 4000 A. at the start of the chemical stripping. Only one experiment (plating and stripping cycle) was performed
in a fifty-milliliter portion of solution. Under our experimental conditions C M ( ~ >,) 5 X lO-'M; t~ could be
Curve B.
-
reproduced to *0.5% provided the electrode was precoated. RESULTS AND DISCUSSION
Solution Medium. 2.50 X lO-'M Hgz(N03)z 0.1M " 0 3 . A num-
+
ber of ions were studied in a supporting electrolyte consisting of 2.50 X
-I-0.c
6 I
I
-1.0
-0.5
I 0.0
LOG 1/J Figure 4. Test of reversibility of Bi(lll)/Bi (amalgam) according to Equation 14a 0 5.00 X 10% Bi(111) and 2.50 X 10-'M Hgz(NOa)z, least squares slope = 0.040 volt, intercept = +0.036 volt VOL 38, NO. 1 1 , OCTOBER 1966
1501
Table 1.
Data Required to Calculate H from Equations 14b and 17
Thallium (Ref.) E’MI(+.)/MUS. SCE, volt Ea, volt XA* YA* YE.*
K (complex constant) 8
icr D,,cm.a/sec.
~ P D Acm.l/sec. , Em US. SCE, volt medium yB,, y A
us. mole fraction
-0.578 (16) $0.003 (22) 0.433 (14) 8 . 3 (14) 0.725 (14) 0 . 4 7 (3) 0.89” 2 . 0 0 (18, 19) 1.60 (24) -0.459 (17) ( 0 . 1 M KNOa)
Lead (Ref.) -0.367
(6) (6) 0.0165 ( 6 ) 0.64 (6) 0.996 (8) 0.066 (3) 0.54* 0 . 9 1 (19) 1.39 (24) -0.383 (7) 0 . 1 M NaNOl lO-sM HClO, +0.006
+
variable, concentration dependence given in (14)
variable, concentration dependence given in (6)
Cadmium (Ref.)
Bismuth (Ref. )
-0.645 ( 1 6 ) +0.051 ( 9 ) 0.098 (10) 1.15 (26) 1 (266) 0.394 (3) 0.BC
0.85 (19) 2.07 (24) -0.578 ( 4 ) 0 . 1 M HNOa
0 . 6 4 (20) 1.62(24) -0.01 (18) 1M HNO,
variable, concentration dependence given in
variable, concentration dependence given in
(26)
(26)
+ NO*-. Cd+* + NOS-
0
Reference (S),assuming TlNOs F! Tl+
c
Reference (3) assuming Cd(NOg)+ $
* Reference (3) assuming Pb(NOs)+ e Pb+2 + NOS-
10-4M Hg,(NO& and 0.1M ” 0 8 . Amalgams were formed by continuous deposition of Tl(T), Pb(II), Cd(II), and Bi(II1). Plots of the terms of Equation 14a (E us. log I / J ) are shown in Figures 2 , 3 , and 4. Two concentrations of thallium ion were studied, 4.00 X 10-6M and 1.00 X 10-5M. The chemical stripping process is reversible (least squares slope of curves gave slopes of 0.060 volt and 0.065 volt, respectively, for curves A and B shown in Figure 2. The intercept, H, is - 0.531 f 0.004 volt us. S.C.E. The calculated value of the intercept using the data listed in Table I, and Equation 14b is -0.529 volt. This agreement is excellent. Calculation of H from Equation 17 using the polarographic data given in Table I yields -0.563 volt, rather poor agreement. Lingane (17) also found poor agreement between experimental El,z data for Tl(1) and calculated values. Line E of Figure 2 corresponds to line A with the assumption that y a / y H B = 1 in Equation 14d. The slope is 0.0785 and demonstrates the need for the inclusion of the activity correction in this case. In this experiment, at t = 0, the mole fraction of thallium in the amalgam was 6.83 X loT2,and YT1 = 2.17 and TH. = 0.973.
The chemical stripping of lead (5.00 10-eM) proceeds reversibly. The least squares experimentd slope of Curve A in Figure 3 is 0.032 volt, and the intercept is -0.431 volt. The theoretical value of the intercept is -0.436 volt according to Equation 14b and -0.440 volt according to Equation 17. The agreement is satisfactory. In the lead experiment, a t t = 0, X p b = 5.15 X YPb = 0.863 and Y H ~ = 0.999. Assumkg T p b / y H g = 1 throughout the stripping process, the observed slope decreases by
x
10%.
1502
ANALYTICAL CHEMISTRY
The chemical stripping of cadmium (1.00 X 10-5M) is reversible. The lesst squares slope of Curve B in Figure 3 is 0.033 volt. The calculated value of the intercept according to Equation 14b is -0.630 volt and is -0.636 volt according to Equation 17, which are in satisfactory agreement with the experimentally obtained intercept of -0.624 volt. At t = 0, Xcd = 6.37 X and yCd/7HB: did not differ appreciably from unity. Bismuth is not stripped reversibly. As seen in Figure 4, the least squares slope of the curve is 0.040 volt, us. the expected value of 0.020 volt. Bi (111) is not reduced reversibly at the dropping mercury electrode. Solution Medium 5.00 X 10-4M Hg(N03), 0,IM “0,. TlGI) was studied in a supporting electrolyte of 5.00 x 10-4x mercuric nitrate and 0.1M nitric acid. Experimental results are shown in Figure 2. Curves C and D indicate that the chemical stripping of thallium amalgams with Hg(I1) is reversible. The average slope equals 0.063 + 0.001 volt when the thallium concentrations were 1.00 x 10-5.1f and 4.00 x 10-5X. The observed average intercept is -0.535 f 0.002 volt, is in good agreement with the results obtained in mercurous nitrate solution and calculatcd according to Equation 14b (-0.529 volt).
+
LITERATURE CITED
(1) Bruckenstein, S., Nagai, T., ANAL. CHEM.33, 1201 (1961). ( 2 ) Christensen, C. R., Anson, F. C., ANAL.CHEM.35, 205 (1963). ( 3 ) Davis, C. W., “Ion Association,” pp. 40, 42, Butterworths, Washington, D. C., 1962. ( 4 ) DeFord, D. D., Anderson, D., J . Am. Chem. SOC.72, 3918 (1950). (5) DeVries, W. T., Van Dalen, E., J . Electroanal. Chem. 8 , 366 (1964).
(6) Hsring, M. M., Hatfield, M. R. Zapponi, P. P., Trans. Electrochem. SOC 75, 12 (1939). ( 7 ) Hershenson, H. M., Smith, M. E., Hume, D. N., J. Am. Chem. SOC.75, 507 f 1953). \ - - - - ,
(8jHoyt, C. S., Stegeman, G., J . Phys.
Chem. 38, 753 (1934). ( 9 ) Hulett, G. A., Trans. Am. Electrochem. SOC. 7, 333 (1905). (10) Hulett, G. A., Delu R. E., J . Am. Chem. SOC.30, 18053905). (11) Kolthoff, I. M., Lingane, J. J., “Polarography,” 2nd ed., Vol. 1, p. 199, Interscience, New York, 1958. (12) Kolthoff, I. M., Lingane, J. J., Ibid., 1st ed., p. 84, 1941. (13) Lewis, G. N., Randall, M.; revised
by Pitzer, Brewer, “Thermodynamics,” 2nd ed., p. 356, McGraw Hill, New York, 1961. (14) Lewis, G. N., Randall, M.,“Thermodynamics,” 1st ed., pp. 267, 270, McGraw Hill, New York, 1923. (15) Lingane:, J. J., “Electroanalytical Chemistry, 2nd ed., p. 410, Interscience, New York, 1958. (16) Lingane, J. J., Ibid., p. 639. (17) Lingane, J. J., J . Am. Chem. SOC.
61, 2099 (1939). (18) Lingane, J. J., IND. ENG. CHEM., ANAL. CHEM.ED. 15, 583 (1943). (19) Meites, L., “Polarographic Techniques,” Appendix B, p. 270, Interscience, New York, 1955. (20) Meites, L., Xeites, T., J . Am. Chem. SOC.72, 3686 (1950). (21) Meyer, F. R., Ronge, G., 2. Angewandte Chem. 52, 637 (1939). (22) Richards, T. W., Daniels, F., J . Am. Chem. SOC.41, 1732 (1919). (23) Roe. D. K., Toni, J. E. A,, ANAL. ‘ CHEM. ’37, 1503 (1965). (24) Stromberg, A. G., Doklady Akad. Nauk SSSR. 85, 831 (1952). (25) Teetes. C . E., J . Am. Chem. SOC. ‘ 53, 3917,‘3927 (1931). (26) Yoshimura, I. C., N i p p o n Kagaku Zasshi 77, 1672 (1956).
RECEIVEDfor review July 11, 1966. Accepted August 8, 1966. Support from the National Science Foundation, E. I. du Pont de Nemours & Co., Inc., and the Procter and Gamble Co. is gratefully acknowledged. Taken in part from a thesis submitted by F. L. Marsh in partial fulfillment of the requirements for the Ph.D.
