May, 1961
ELECTRON EXCHANGE OF ANTIMONY (111)-(V)
The calculated mean activity coefficients and the smoothed osmotic coefficients are given in Table 11. The y* are somewhat higher than were obtained for the other 3-1 salts (e.g., ref. 3 and ref. 4 ch. 13). These slightly higher values are also obtained if the data are fitted to d = 4.0, B = 0.9 and the lny*
I N A C I D SOLUTION
867
are determined by calculation to m = 0.1879 and by graphical integration on to saturation. Comparison of the observed osmotic coefficients with those of other 3-1 electrolytes, reveals differences (as much as 4.7% a t 0.05 m, less a t higher concentrations) which indicate the individuality of this salt. --
THE ELECTRON EXCH911’GE REACTIOK BETWEEK AKTIMOSY (111)AXD ,4STIMONY (V) IS SULFURIC-HYDROCHLORIC ,1CID MIXTURES BY C. H. BRUBAKEIL JR., ASD J. A. SIXCICS Kedzie Chemical Laboratory, Michigan State Unzversity, East Lanszny, Mzchzgan Receized December 17, 1960
No antimony exchange is observed in sulfuric acid solutions between 3 and 12 JI. When chloride is added to the solutions, (H’) = 9.75 M, exchange occurs and the rate increases as (Cl-) increases. In the intermediate range, 0 4 < (Cl-) < 6 M, the graphs of the McKay equation are not linear and suggest compleu, competing reactions. The exchange is first order in Sb(II1) and, a t (Cl-) > 6.00 M , also in Sb(V). B t lower (Cl-), the order in Sb(V) falls to 3/4. Dependence of rate of exchange on (SO,=) and (H+) is complex and exhibits a maximum in each case. There is second-order dependence on (Cl-) below 0.200 31 C1- and the order in (Cl-) gradually falls off above 0.200 M . Spectrophotometric studies indicate that solutions of Sb(V) in H2S04and H2SOrHCl mixtures are complex. Beer’s law is obeyed by Sb(II1) solutions. Sb(1II)Sb(V) mixtures have spectra which are the sums of individual spectra; %.e.,in these solutions, no interaction spectra are observed. Semimicro separations of Sb(II1)-Sb(V) mixtures have been developed and are discussed.
In this Laboratory we have been studying elect’roii exchange reactions (in two electron systems) in the presence and absence of complexing anions, which might also serve as bridges between the species in two different oxidation st’ates. For example, recent experiments have concerned the Sn(I1)-Sn(1V) exchange in sulfuric acid1 and the effects of organic oxyacids2 on the Tl(1)-Tl(II1) exchange in perchloric acid solutions. Previously the Sb(II1)-Sb(T’) exchange in hydrochloric acid solutions had been examined by Bonner and co-workers,3 Seunianii and Brown4 and by Cheek5 Exchange in HC1 solutions is complex and is made so by competing hydrolysis reactions, which are slow. The present work was undertaken to determine whet’her or not the Sb(II1)-Sb(T’) exchange occurs without the presence of complexiiig agents and whether or not it might be suitable for work paralleling the studies of anion effects on the tin and t’halliumsystems. Experimental Materials .-Antimony and antimony trioside were Baker and A4damsonreagent grades, sulfuric and hydrochloric acids were reagent grades from E. I. du Pont de Semours and Co., perchloric acid was from Mallinckrodt. Lithium perchlorate was prepared as before’ from Mallinckrodt, A . R., lithium carbonate and perchloric acid. Lithium sulfate was Fisher “certified” analytical grade material. “Thionalidr,” a-mercapto-N-2-naphthalerie, was Eastm i n Kodak #5828 and 8-hydroxyquinoline was Eastmari .._____~..
+7W. “Cupferron,” ammonium nitrosophenylhydroxylamine was J. T. Baker “Analyzed.” All other chemicals (which were not used in actual kinetics experiments) were reagent grade materials, used without further treatment, other than drying when required, or xere prepared as described below. The Sblzj tracer was obtained from Oak Ridge in lots of 0.4 mc. of Sb12j in 6.2 g. of t,in metal. Separation of the antimony tracer from the large amounts of tin was effected by fractional sulfide precipitation of antimony tracer plus 22 mg. of antimony carrier from a solution in which the tin was present as the tin (IV) oxalate complex.6 Each unit of Sb125and tin metal was dissolved in 25 ml. of concd. HC1, 5 ml. of 12 &If ELSO, containing 22 mg. of Sb(II1) carrier was added and the tin was oxidized to the tin(IV) state with excess, elemental bromine. h hot solution containing 120 g. of H2C204,2H20 and 20 g. of KOH in 100 ml. of water was added and the antimony mas precipitated by an H2S pressure t e ~ h n i q u c . ~The Sb& was separated and washed by centrifugation. Another addition of antimony carrier was made to the filtrate and a second sulfide precipitate 15-as collected. The combined sulfides were dissolved in 5 ml. of concd. H2S0, and w r e reprecipitated from a medium containing 10 g. of H2C’?O4.2H?O in 100 nil. of solution. These second sulfide precipitates from three 0.4 nic. units were combined and dkolved in 30 ml. of hot, concd. H2SO4, yielding a stock solution containing approximately 0.15 g. of Sb(II1) in 25 ml. of concd. H2S04. Radiochemical purity of the second sulfide precipitate was determined by an aluminum absorption curve: range 220 mg./cm.2 corresponding to a maximum energy of 0.61 l l e v . (c!., 0.616 M e V . literatnre vnlue8). d half-life determination carried out over an eight month period yielded 2.6 i 0.2 y. compared to 2 . 7 J - . ~ Preparation of Solutions.--.1Iitimon!.(III) stocks wereprrpared from Sbe(S04),j. A4ntimonymetal was dissolved i n hot, concd. TI,SOI. The white crystalline Sb2(S04), precipitated on cooling, :parated by filtration through fritted glass and W ~ re F zed twice from mnc-d. Ff,S0, . g
11) G. Gordon and (’. 1 1 . Hriibakvr, J r . , .J. AWL.Chem. SOC., 89, 4148 11960). ( 2 ) C’. t1. Hruhnker. .Ir.. and C. :indrade, ibid., 81, 5282 11!459). 71, 3909 (1919): N. A. Bonner and N-. . _. ion of Inorganir Chemistry, 136th National 16) TV. W. Scott, “Standard Methods of Cheinical Ana Meeting, Anierican Chemical Society, Atlantic C i t i , Sept. 13 to 18 I X . , D. Van Kobtrand Co. Inc., S e n T o r k , X. Y., 1 9 3 9 pi) (1959); N. .4. Bonrier a n d K. Goishi. J . .4m. Chem. Soc., 83, 8.5 ( 7 ) A. I. Vogel, “ N a r r o and Semi-Jlicro Qualitative (1961). 4 t h Ed., Longnians, Green and Co., New l o r k , N. Y . , 1953. t &) H. AI. Neuniann a n d H. Brown, ibid.. 78. 1843 (1956). ( 5 ) C. H. Cheek, P1i.D. dissertation, TVashington Univerbity, S t . (8) G. Friedlander and J. W . Kennedy, ”Nuclear and Radiocliernistry,” .John Wiley and Sons, Inc., New P o r k , N. Y., 1955. Louis. X o . , 1953.
C.H. BRUBAKER, JR.,AND J. A. SINCIUS
T‘ol. 65
Antimony( 111) sulfate stocks were repared by treating a t 0’ to minimize decomposition and no solution was kept excess Sb2(S04)3with hot, 12 M HzS& and filtering off the for more than 8 hours. h 5-ni1. aliquot of exchanging soluexcess on a fritted glass filter. A small amount of 12 M tion was pipetted into a 125-ml. separatory funnel which H&04 then m-as added t o the filtrates t o reduce the concen- contained 70 ml. of ice-cold water and 5 ml. of cupferron tration below saturation. Two such stock solutions were solution. The mixture was shaken and the Sb(II1) was prepared and contained 0.0368 and 0.0595 M Sb(II1) in thus precipitated aa the cupferrate. The mixture then was 12.76 and 12.74 M H2S04,respectively. These solutions shaken for 30 sec. with 5 ml. of reagent grade HCCl, and were stable, with respect t o hydrolysis, for more than a the HCCla layer was separated and filtered through a glassyear; solutions prepared from Sb20a or from hydrolyzed wool plug into a IO-ml. volumetric flask. Another 5-ml. Sb,(S04)3 are not, even after treatment of the oxide with portion of cupferron was added and the mixture was exhot, concd. H2S3,. Presumably the hydrolysis is only tracted with 4 ml. of CHC1, and the CHC13layer was sepaslowly reversed. rated and added to the first extract. A third, 1.5 ml. of More than a little difficulty was encountered in arriving CHCla, extraction was made. The glass wool plug was a t a method of preparing Sb(V) sulfate solutions, but a washed with ml. of CHC13 and the combined extracts method of using “peroxysulfuric acid,” which was finally were made up to 10 ml. A 4.00-ml. sample of this was devised, proved satisfactory. placed in a one dram, screw-cap vial. The vial then was Peroxydisulfuric acid solutions n-ere produced by a high stoppered with a cork, which was coated y i t h Goodyear current-density, anodic oxidation of sulfuric acid .lo The “Pliobond” adhesive and covered with aluminum foll before anode was a 1 cm. length of heavy platinum wire; the cath- the screw-cap was put in place. Without such precautions ode, a spiral of 15 cm. of finer wire. A 6 v. storage battery considerable evaporation of the C€ICl3occurred and changed was used, a t full capacity, to provide the electricity. 9 M sample geometry. IM04was cooled in an ice-bath and was electrolyzed at 1.5 It was found that it was absolutely necessary to maintain smp. for 8 hours. Current efficiencies of about 33% were solutions near 0’ until after the counting aliquot sample was obtained, based on total oxidizing power of the solutions. taken. If the solutions were allowed to grow warm, deImmediately after the electrolysis, the “peroxy-acid” composition of the antimony( 111) cupferrate occurred and solution was added in two or threefold excess to Sb(II1) in various errors were ~ b s e r v e d . ’ ~ 12 M H2S04and the mixture was allowed to stand for about I n mounting samples of the 4.00-nil. aliquots for Y 12 hours. Then, gentle heat was applied until oxygen evolu- counting the samples were always placed in new vials. tion ceased, after which heating was increased to concen- An NaI (TU)well-type scintillation counter was used and at trate the Sb(V). Except when the solutions were very least l o 4counts mere recorded for each sample. All samples dilute, this heating resulted in the appearance of a fine were counted within two hours of separation, so no corwhite solid which slowly dissolved. Stock solutions, pre- rection for Sb125decay was made. pared in this way, contained 0.05-0.08 M Sb(V) although Because of long half-lives for the exchange, equilibrium, higher concentrations could be obtained. These stocks or infinite-time, activities, A,, were calculated from the were stable, with time, toward hydrolysis. initial radioactivity A0 and the concentrations (Sb”1) and Because of the complexity of this system, Sb(V) solutions (Sbv); A , = Ao(SblII)/[(Sb[I1) (SbV)]. Eight to fourwere prepared with Sb125 initially present. An appropriate teen samples were taken within two to three half-lives and quantity of Sblz solution was added to Sb(V) in H2S04 standard McKay graphs were used to determine the rate of and the “peroxy-acid” oxidation was repeated, thus giving exchange .I4 reasonable assurance of chemical identity of the Sb(V) Spectrophotometric Studies.-For qualitative studies a species. This product was diluted to give a solution 12 Beckman model DK-2 instrument was used, for quantiA/ in H2S04. tative work the model DU, with matched, ground-glassPreparation of Solutions for Exchange .-For each ex- stoppered, 1 cm., quartz cells was employed. change experiment, two individual Sb(II1) and Sb(V) soluAcidity Functions.-Ho’s, Hammett’s acidity functions, tions were prepared in 50-ml. volumetric flasks. Each for a number of the acid-salt mixtures, used as media for the pair was identical except for antimony content. Solutions exchange studies, were determined by the methods of Hamn-ere mired with salts, acids and antimony and were brought mett and co-w0rkers.1~ The indicator was 2,4-dinitroto the appropriate temperature and then were diluted t o aniline, whichserved in the range 8 < (H’) < 11. Measurevolume with water. These solutions were allowed to stand ments were made with a Duboscq colorimeter. for 12 hours and then equal portions of these Sb(II1) and Analytical Methods.-Acids were standardized, after Sb(V) stocks were mixed a t “zero time.” being diluted volumetrically, against 0.5 S potaseium acid Separation of Sb(II1) and Sb(V).-The solutions in this phthalate. Antimony(II1) was determined bp titration study were 1/10 to 1/100 the concentration used by pre- with 0.1 N KBr03 (primary standard grade) in 2-3 N HC1 vious workers, so special separation techniques had to be and with use of naphthol blue-black as an indicator. Antideveloped or adapted. Three distinct methods were em- mony(V) was reduced with hTaHSO3, the excess so?was ployed. In the first method, thiondide (@-aminonaphthalide boiled off and then the Sb(II1) was determined as above. of thioglycolic acid) was employed to precipitate the Sb- When determinations of very dilute solutions were needed, (111) as Sb(C12HloONS)3.1‘The precipitation of Sb(V) was a colorimetric method for Sb14-was applied.16 prevented by adding K F in order to form SbFe’. This Chloride was determined by a modified I’olhard method1? iiiethod was satisfactory in the absence of chloride, but in with the Sb, when present, complexed with tartrate. the presence of chloride considerable “induced exchange” Sulfate was determined as 13aS04; Sh was rc3moved m i rendered the method less ideal. A second method made use fin(, iron wire, when this was necessary. of 8-hydroxyquinoline to precipitate Sb(III),ll but Sb(II1) carrier had to be added for precipitation and “induced Results exchange’’ became appreciable when chloride was added. Seven experiments were carried out in suli’uric: The above methods were used, but the third method was rmployed to obtain all rate data reported below. The suc- acid solutions ranging in concentration froin 2.97 ressful separation method involved precipitation of Sb(II1) to 12.0 M ; [Sb(III)] was between 2.00 and 10.0 X with cupferron (ammonium nitrosophenylhydroxylamine) . [Sb(V)] in the same range. No eschangc The Sb(II1) cupferrate mas evtracted with HCCl, and an aliquot of the extract was taken for ?-scintillation counting.12 was observed in any of these solutions, two of Cupferron was prepared in a 170 solution which was stored which (6.00 and 12.0 dB H,S04) mere follonwl
+
(0) W. E. Thorneycroft, “Textbook of Inorgariic Chemistry,” J. N. lriend. ed., Vol. VI, part V, p. 111, J. 13. Lippincott Co., Philadelphia. 1936. (IO) W. C. Schunib, C. N. Sittterfield and R. L. Wentworth, “Hydrogen Peroxide,” 2nd edition, Reinhold Publ. Carp., New York, N. Y . , 1955. (11) J. F. Flagg, “Organic Reagents,” Interscience Publishers, New York, N. Y . , 1948. (12) N. H. Furman. W. B. Mason and J. S. Pekola, A n d . Chem., 31, 1325 (1949).
for over 1500 hours and others were observed f o r (13) J. 8. Frits, h1. J. Richard and A. S. Iiystrofl, i h d . , 29, 677 (1957). (14) Ref. 8, pp. 315-317. (15) L. P. Hammett and A. J . Deyrup, J . Am. Chem. Sac., 64, 2721 (1932); L. P. Ilammett and hl. -4. Paul, ibid., 66, 827 (1831). (16) E. 1%‘. IZIcChesney, I n d . 8 n g . Chem., Anal. Ed., 18,116 (1946); A. Elkind, K. H. Gayer and D. F. Boltz, A n d . Cham., 26, 1746 (1953). (17) J. R. Caldwell and H. V. Moyer, Ind. Eng. Chem., Anal. Ed.. 7 , 38 (1935).
ELECTRON EXCHANGE OF ANTIMONY(III)-(V) IN ACIDSOLUTION
May, 1061
variously 73, 82, 133, 787, 813 hours. I n several cases cloudiness began to appear a t long times (after samplings were terminated). Since there was no detectable exchange in sulfuric acid alone, the effect of chloride ion on the system was evaluated. As chloride ion was introduced, exchange was detected with the halflife falling from 7522 hours with 0.025 M C1- to 7.62 hours with 6.00 M C1-. These results for 25' are given in Table I.
0.9 0.8
TABLEI I VARIATIONOF EXCHANGE RATEWITH CHLORIDECONCEN-
d0.3
TRATION
- .
io-3'M; 24.80 & 0:020 [a-1, M None" 0.025" .05" .IO=
. lja .20b .30" .40"
.40 .50" .60" .60 .70 .80 1.00 1.50 2.00 2.00 2.00 2.00 3.00" 4.00" 5,OO" 6.00 6.00 [Sb(V)]
tl/
-
M
P,
(hr.)
869
t
1
.. R
(moles/l.-hr.)
No exchange obsd. in 1700 hr. 7522 5.99 x 10-8 2048 2.20 x 10-7 463 9.72 x 10-7 173 2.60 X lo4 118 3.82 X IO4 66.3 6.79 x 1 0 4 39.9 1.13 X IO-& 40.1 1 . 1 3 X lo-' 31.7 1.42 X 23.3 1.92 X 35.0 1.74 X 26.7 1.69 X 21.2 2.13 X 10-6 20.6 2.20 x 10-5 12.0 3.77 x 10-6 11.2 4.02 x 10.8 4.19 X 10.G 4.27 x 10-6 10.2 4.43 x 10-6 10.2 4.42 X 10-6 9.33 4.83 x 10-6 8.75 5.15 X 6.10 7.41 x 7.62 5.93 x 10-6 = 1.29 X 10-3 M. * Bverage of 11 runs.
Initially the exchange appears to be second order in (Cl-); Le., a graph of log R us. log (Cl-) has a slope of 2.05 up to (C1-) = 0.200 M . The slope then falls steadily until i t reaches a value of 0.28 in the range 1.50 to 6.00 M . Some experiments were also run at 42.0 f 0.1'. For two solutions with 0.200 M C1- (as in Table I) the average exchange half-life was 55.8 hr. ( R = 8.15 X 111 hr.-*) and for 2.00 d l C1-, 2.11 hr. ( R = 2.15 X 10-4M hr.-l). Graphs of the McKay equation to give the data a t 25 and 42' were not always linear to long times, e.g., see Fig. 1. Data for the solut,ions with (Cl-) less than 0.400 X or more than 6.00 M gave linear McKay plots to two or more half-lives, but when 0.400
