November 15,1933
I N DUSTR I A L A ND ENGI N EER I N G CHEM ISTR Y
can be readily mastered by any person experienced in laborstory methods. The time required for a test compares favorably with the sinking-time method. A series of five individual determinations, required for the determination of the efficiency a t a given concentration, may be made in 15 to 20 minutes, depending naturally upon the length of the actual sinking-time observed.
. LITERATURE CITED (1) Auerbach, Melliand Textilber., 7, 681, 775 (1926). (2) Draves and Clarkson, Am. Dyestuff Reptr., 20, 201 (1931).
381
(3) Goodwin, “Precision Measurements and Graphical Methods,” p. 19, McGraw-Hill, 1920.
(4) Herbig, “ d e und Fette in der Textilindustrie,” Wissensohaftliahe Verlagsgesellschaft, p. 422, Stuttgart, 1929.
(5) Herbig and Seyferth, Melliand Textilber., 8, 45, 149 (1927). (6) Ibid., 9, 921 (1928). 71 775 (7) Kind and Auerbach* zbid*v (8) Lenher, Am. Dyestuff Reptr., 22, 13 (1933). (9) Ristenpart and Petrold, 2.ges. Textil-Ind., 29, 176 (1926). (10) Seck and Lachmann, Melliand Textilber., 7, 851 (1926). (11) Stiioker, Zbid., 13, 152 (1932).
RECEIVED June 8, 1933.
Antimony as an Indicator Electrode in Potentiometric Titration of Iron and Aluminum E. W. KANNING AND F. H. KRATLI, Indiana University, Bloomington, Ind.
A
N T I M O N Y has been found by many investi-
s a t u r a t e d calomel electrode, The titration Vessel consisted Of an open 400-cc. beaker. The potential of the electrode bination was measured by means of a students’ type Leeds and Northrup potentiometer, NO. 7651,in conjunction with a LeedB and Northrup galvanometer No. 2310. I n all cases, unless otherwiseindicated, the solutions were kept continually agitated by means of a current of air bubbling through the solution in the titration vessel. All experiments were carried out a t room temperature, which varied from 24” to 28” C.
The antimony electrode is applied as indicator electrode to the direct titration of ferric chloride and aluminum chloride with sodium hydroxide solution. Data are given which show the general suitability of the antimony electrode for the titration f aluminum and iron chlorides. The method also affords an approximate analysis of of the two
be adapted as an indicatortoelectrode to the potentiometric titrations of acids and bases and to the determination of the pH of various solutions. The antimony electrode has also found application in a number of titrations involvingprecipitation reactions. In the titration of aluminum and magnesium chlorides with sodium hydroxide solution, Treadwell and Bernasconi (3) have found that in the titration of aluminum chloride two jumps in the antimony electrode potential occur, one when the duminum hydroxide has been quantitatively precipitated, and one, which is less pronounced, when the aluminate has been produced. I n the titration of mixtures of aluminum and magnesium chlorides with sodium hydroxide, jumps in the electrode potential occur a t the precipitation of aluminum and magnesium hydroxides, respectively, the second jump being too early, causing an error of from 1 to 2 per cent. The antimony electrode has been found by Malvea and Withrow (2) to be satisfactory to indicate the end points in the titration of mixtures of calcium and magnesium with sodium hydroxide solution, An abnormal titration curve occurs, according to Elder (I), for the antimony electrode in acid solutions of ferric chloride, probably because of the presence of pentavalent antimony in solution. The purpose of this investigation is to show the application of antimony as an indicator electrode in the precipitation of ferric iron and aluminum from neutral solutions of their chlorides by the addition of sodium hydroxide solutions.
PROCEDURE The titrations were carried out using antimony as the indicator electrode. The electrode was prepared from electrolytically refined antimony by casting in a carbon mold, and undoubtedly contained some oxide; however, no precaution was taken to exclude the oxide from the cast metallic rod. The electrode had a length of 4.5 inches (11.25 cm.) and a diameter of 0.25 inch (0.63 cm.). I n all the titrations the potential of the indicator electrode was measured against the
Three stock solutions of ferric and aluminum chloride were pre ared having the following normalities with respect to iron anzaluminum: ferric chloride, 0.3146 N, 0.9969 N, and 0.1000 N ; aluminum chloride, 0.2968 N , 1.0045 N , and 0.1000 N . The aluminum chloride solutions were standardized gravimetrically and the ferric chloride solutions by reduction with stannous chloride and titration with potassium bichromate solution. A determination of the chloride content of the ferric and aluminum chlorides used in preparing the stock solutions indicated that the error encountered in the calculation of the theoretical quantity of the sodium hydroxide solutions required for the samples of ferric and aluminum chlorides titrated was of little consequence, since the commercial Pparations of ferric and aluminum chlorides used containe an undeterminable amount of basic salts. Titrations of various quantities of ferric and aluminum chlorides, both separately and as mixtures, were carried out using sodium hydroxide solutions approximately 1 N , 0.5 N , and 0.1 N . These solutions were prepared from carbonate-free sodium hydroxide and carbon dioxide-free water and were standardized against pure recrystallized succinic acid, using phenolphthalein as indicator. The stren hs of the various sodium hydroxide solutions are shown in t e tables.
F
Three series of experiments were carried out, involving sodium hydroxide solution approximately 0.5 N , and 1 N , and 0.1 N,respectively. I n the first series the effect of the presence of sodium and ammonium sulfate was also determined. Because of the difference in solubilities of ferric and aluminum hydroxide, the ferric hydroxide was found to be quantitatively precipitated first, giving rise to a jump in the potential of the antimony electrode a t the iron equivalence point.
ANALYTICAL EDITION
382
I
I
I
I
Vol. 5, No. 6
Curves for the titrations in this first series of experiments, which are typical of the curves in all the titrations in this investigation, are shown in Figures 1 , 2 , 3 , and 4. The determination of the end points is shown and it is seen that the accuracy of the end point is largely dependent upon the correct interpretation of the curve. The differential curve gives a much more definite determination of the end points, since it brings out more clearly the points of maximum increase in potential of the indicator electrode.
I
TABLE11. SERIES2
OF
TITRATIONS
VOL. OF NaOKb VOL. OF NaOHb
.400
THEORETICALLYACTUALLY PRESENT^ REQUIRED USED ERROR FeCla AlCla FeCls AlCla FeCla AlCla FeCla AlCla Grams Grams Cc. Cc. Co. Cc. % % 0.5390 0,4460 11.10 11.19 11.20 11.20 +0.90 +0.08 16 1.0780 0.4460 22.20 11.19 21.60 11.40 -2.70 11.84 17 11.00 22.50 -0.90 +0.52 0.5390 0.8920 11.10 22.38 18 1.0780 0,8920 22.20 22.38 21.60 22.70 -2.70 +1.41 19C 0.2695 1,1150 4.52 22.80 4.40 22.40 -2.70 +2.23 20 4.56 5.00 -0.55 +9.67 1.3475 0.2230 22.62 22.50 21 10.30 11.30 -13.80 1-23.90 22d 0.5390 0.4460 9.05 9.12 a I n all cases volume of titration solution was 100 cc. a t the start. b 0.8972 N NaOH used. c I n experiments 19 to 21, inclusive, 1.1012 N NaOH wan used. d Hydrogen electrode used.
EXPT.
.SO0
.zoo .140
0
5 00.
10 NaOR
15
TABLE111. SERIES 3
20
FIGURE 1. E. M. F.-VOLUME CURVE FOR TITRATION OF ALUMINUM CHLORIDE WITH SODIUM HYDROXIDE SOLUTION (EXPERIMENT 3, TABLEI)
OF
TITRATIONS
VOL. O F VOL. OF NaOHa NaOHa VOL. THEORETICALLY ACTUALLY OF P R ~ S E N T REQUIRED USED ERROR EXPT.SOLN. FeCla AlCls FeCla AlCls FeCla AlCh FeCla AlCla Cc. Grams Grams Cc. Cc. Cc. Cc. % % 11.80 . +0.17 11.78 0 1 50 0 0.3297 0 11.70 . . -0.68 11.78 0 0 2 75 0 0.3297 11.80 4-0.17 11.78 0 0 0.3297 0 3 125 -0.72 .. 12.40 0 12.49 0 4 50 0,4250 0 fO.08 .. 12.60 0 0 12.49 0 5 75 0.4250 -0.72 12.40 0 0 12.49 0 6 125 0.4250 7 150 0.4250 0.3297 12.49 11.78 12.40 11.80 -0.72 40:i7 8 150 0.8500 0.3297 24.98 11.78 24.98 11.90 0.00 f l . 0 2 9 150 0.4250 0.6594 12.49 23.56 11.90 24.00 -4.72 4-1.87 10b 150 0.4250 0.6594 12.49 23.56 11.80 23.40 -5.52 -0.67 1 1 0 , d 125 0 1.8275 0 27.00 0 26.60 . . -1.48 0 1.8275 0 27.00 0 26.60 . . .. -1.48 12: 125 28.60 0 29.00 0 4-1 39 13 125 1.3519 0 i4c 125 0.6759 0.9137 14.20 13.50 13.00 16.00 -8:45 +ii:ii 15f 125 0.6759 0.9137 14.20 13.50 12.80 13.40 -9.85 -0.74 a 0.6297 N NaOH used b 25 cc. of 16 per cent NH4Cl solution added. C 2 grams of NasSOt added, d I n experiments 11 to 15, inclusive, 0 5059 N NaOH was used. e 1 gram of NazSOi added. f 2 grams of (NHa)zSOa added.
.. . .. .. . .
TITRATIONB
TRLIORETICALLY ACTUALLY PRESENT^ REQUIRED USED ERROR FeCls AlCls FeCla AlCls FeCls AlCla FeCla AlCla Gram Gram Cc. Cc. Cc. Cc. % % 0.0540 0.0444 10.00 10.00 10.10 10.10 f l . O O +1.00 23 0.0270 0.1111 6.00 25.00 4.80 25.20 -4.00 +0.80 24 5.00 26.00 5.30 $4.00 +6.00 25 0.1352 0.0222 26.00 0.1081 0.0889 20.00 20.00 19.90 20.20 -0.60 +1.00 26C 0,1081 0.0889 20.00 20.00 19.80 20.70 -1.00 27d +3.50 a Volume of solution at start of titration, 100 00. b 0.1 N NaOH used. c Agitated with a stream of hydrogen bubbling through solution. d Hydrogen electrode used in this experiment.
EXPT.
The precipitation of the aluminum hydroxide followed and the second jump in the potential appeared a t the quantitative formation of aluminum hydroxide. I n the case of the titration of aluminum chloride alone, two jumps in the potential appeared, as found by Treadwell and Bernasconi, one when aluminum hydroxide was quantitatively precipitated, and a second less pronounced jump when the aluminate was produced. The second jump appeared to be rather indistinct and unsuitable for accurate determinations. I n the case of the titration of ferric chloride alone, only one jump in the potential occurred, the one at the quantitative precipitation of ferric hydroxide. TABLEI. SERIEB 1
OF
VOL.OF NaOHb VOL.OF NaOHb
..
..
..
I n order to determine the end point of each reaction, curves were constructed with e. m. f. of the electrode combination plotted as ordinates and volume of sodium hydroxide solution as abscissas. The definite location of the point of maximum increase in potential was determined from these curves by means of the oscillatory tangent to the curve and also from differential curves in which the volume of sodium hydroxide solution was plotted against the change of potential with unit change of volume of sodium hydroxide (AEIAV).
In the second series of experiments the titrations were made with sodium hydroxide of approximately normal s t r e n g t h . More f e r r i c and alumin u m chlorides , were present t h a n i n t h e first s e r i e s of e x p e r i m e n t s . In t h i s series of titrations, various mixtures of ferric and aluminum chloride were used, a n d t h e d a t a in Table I1 show the results obtained. The third series of experiments w a s c a r r i e d o u t with 0.10 N sodium hydroxide solution and more dilute solutions of ferric and aluminum chlorides. As in t h e s e c o n d series, one titration was made using the hydrogen electrode in order to make a comparison with the 0 10 NaOH 20 30 antimony electrode. FIGURE 2. E. M. F.-VOLUME CURVE Table I11 gives the FOR TITRATION OF FERRIC CHLORIDE d a t a for the titraWITH SODIUN HYDROXIDE SOLUTION tions in series 3. (EXPERIMENT 6, TABLEI) Oc.
I N D U S T R I A L A N D E N G I N E E R I N G C H €4 M I S T R Y
November 15,1933
RESULTS The data given in the tables indicate that antimony is suitable as an indicator electrode in the potentiometric titration of either aluminum or ferric chloride with sodium hydroxide solution. The end point is clearly defined and accurately located by the jump in the electrode potential a t the quantitative precipitation of the hydroxides. The slight jump in
0
LO
20 c c . NaOH
30
383
seen from Table I. I n the case of mixtures of aluminum and ferric chlorides, the presence of sodium sulfate caused errors of from 8 to 11 per cent, making the method prohibitive in the presence of this alkali sulfate. The presence of ammonium sulfate had an effect similar to that of sodium sulfate. Normal titration curves were obtained in the experiments in which sodium and aluminum sulfate was added. The strength of the sodium hydroxide solution used for the titrations and the amounts of ferric and aluminum chlorides present in the solutions to be titrated seem to have, in general, little effect on the suitability of antimony as the indicator electrode (Table I). The hydrogen electrode was found to be inferior to the antimony electrode for the direct titration of iron and aluminum by sodium hydroxide, especially in concentrated solutions, probably because the platinized surface is poisoned by the salts in solution. I n more dilute solutions, the hydrogen electrode behaves in the Rame manner as the antimony electrode but exhibits no advantages. Stirring by means of air was found to be a suitable method of causing agitation during the titrations. There was no perceptible difference in the action of the antimony electrode where hydrogen was used in place of air.
40
FIGURE 3. E. M.F.-VOLUME CURVEFOR TITRATION OF MIXTURE OF ALUMINUM AND FERRIC CHLORIDEWITH SODIUM HYDROXIDE SOLUTION (EXPERIMENT 7, TABLEI)
potential (Figure 1)a t the equivalence point for the aluminate formation is less distinct and practically imperceptible in the case of mixtures of aluminum and ferric chlorides and is not satisfactory, under the conditions of these experiments, for the determination of the end point. Dilution seems to have little effect upon the accuracy of the method. I n general it was found that in the titrations involving mixtures of aluminum and ferric chlorides, the end point indicating the equivalence point for ferric hydroxide was too early and the end point for aluminum hydroxide too late. I n all cases the jump in the electrode potential a t the ferric hydroxide equivalence point was less pronounced. The potentiometric titration of mixtures of ferric and aluminum chlorides with sodium hydroxide, using an antiinony indicator electrode, affords a method for an approximate analysis. Titration errors occur which prohibit a more accurate analysis. The accuracy is greater when nearly equal proportions of the two salts are titrated, probably because the titration curves can be more easily interpreted. The accuracy is no doubt impaired by the formation of basic salts a t the location of the jump in potential, since no precautions were taken to prevent this difficulty a t the end point. Evil dence of the formation of basic salts is clearly indicated by the small jump in potential immediately before the aluminum end point in Figure 4. The presence of sodium sulfate in the solutions of either aluminum or ferric chloride caused an increased error, as is
0
10
20
30
40
c c . iiaOH
CURVEFOR TITRAFIGURE 4. DIFFERENTIAL TION IN FIGURE 3
The potential of the antimony electrode reached equilibrium rapidly, except at the very start of the titrations. The presence of a relatively large quantity of iron in the solution seemed to affect the electrode, causing it to be covered with a dark coating. When most of the iron had been precipitated, the dark coating disappeared and the potential of the electrode thereafter reached equilibrium almost immediately after the successive additions of sodium hydroxide solution, I n contrast to this, when the hydrogen electrode was used equilibrium mas reached only after 10 to 15 minutes throughout the entire titration. This fact, together with the other factors above mentioned, points favorably to the use of the antimony electrode for the titration of ferric and aluminum chlorides with sodium hydroxide. LITERATURE CITED (1) Elder, Trans. Am. Electrochem. SOC.,57, 383 (1930). (2) Malvea, B. B., and Withrow, James R., J. Am. Chem. Soc., 54, 2243 (1930). (3) Treadwell, W. D., and Bernasconi, E., Helv. Chim. Acta, 13, 500 (1930). RBCEIVIOD September 28. 1932.
