722
EUGENE L. COLICHMAN
Vol. 74
claudetite, or other common ABXa structures the stable phase. We were unable to prepare or which were examined for analogies. The symmetry prove the existence of Ga203.3H20,but in other reof e-Gaz03is apparently lower than hexagonal or spects our data agree with those of Laubengayer tetragonal. That e-GaZO3 is not merely a chance and Engle. Only one monohydrate, Ga02H comintermediate structure obtained under very specific pletely analogous to A102H,diaspore, was obtained ; conditions, but is a definite structure is borne out under no conditions could we obtain a boehmite by the fact that when GaA103, or its solid solutions structure. Data obtained from some 200 runs have with Ga203and Alz03,is heated in air 100’ above extended the work to pressures from 50 to 26,000 the equilibrium transformation temperature, a ser- p s i . up to 800’. Starting from a-Gaz03,6-Ga203, ies of €-phase solid solutions form,‘ showing a regu- Ga02Hand gels, with time of reaction varying from lar displacement of lines in the X-ray pattern with half an hour to over two weeks, GaOzH was obtained below and P-GazO3 above 300 f 6’. Presincreasing aluminum content. Using a furnace adapted for use with the X-ray sure had very little effect on the decomposition spectrometer, the pattern of 6-Ga203was found to temperature of Ga02H. The possible existence of a disappear and that of s-Ga203appear a t 525’ within low-pressure stability field for cr-GazO3 was investi30 minutes. This inversion was effected a t 500’ but gated. At pressures as low as 50 p s i . the convernot a t 475’ when held a t temperature for one week. sion of cu-GazO3and GaOsH to p-Ga203was realized. The inversion of e-GazOsto P-Ga203occurs readily Failure to obtain the conversion a t 15 p.s.i. pressure is ascribed to sluggishness of the reaction. The a t 870 f 15’ with a marked heat effect. Equilibrium Relations in the System Gaz03- equilibrium diagram has only two fields, those for HzO.-Laubengayer and EngleI4investigated phase /3-Ga203 and Ga02H, separated by a univariant relations in the system Ga203--H20 using closed line a t 300 f 5’. Acknowledgment.-This investigation is part bombs and under limited pressure conditions. They reported the Occurrence of a metastable trihydrate of a research program on the stability relations of obtained a t 170’, and a monohydrate stable from minerals a t high pressure and temperature, sponroom temperature to 300°, above which P-GaZO3is sored by the Geophysics Branch of the Office of Naval Research. (14) A. W.Laubengayer and H. R. Engle, TEISJOURNAL, 61, 1210 STATE COLLEGE, PENNSYLVANIA RECEIVED JULY 26, 1951
(1939).
[CONTRIBUTION FROM THE CHEMISTRY
DEPARTXENT OF THE UNIVERSITY OF
PORTLAND]
Polarographic Maxima Suppression in Alcohol-Water Mixtures BY EUGENEL. COLICHMAN The various factors involved and their influences on polarographic maxima are studied here. The concentrations of colloidal agents necessary t o suppress maxima, the M.S.P. values, are seen t o increase with increasing alcohol content of the solvent. A linear relationship is noted. An empirical maxima suppression equation is deduced and discussed. The results are interpreted in terms of previously reported micelle phenomena.
The relationship between maxima suppression and micelle formation (for colloidal type suppressors) was examined and reported’ earlier. The suppressor concentration, precisely sufficient to eliminate the maximum under consideration, has been termed the maximum suppression point (M.S.P.). It has been shown that in order to avoid possible. misinterpretation of polarographic results, particular attention should be given to the quantity of suppressor used. For each given suppressor, the role played by: (a) the reducible species, (b) the supporting electrolyte, and (c) the solvent, in relation to the maximum suppression point (M.S.P.), bears investigation. The present report deals with this problem in alcohol-water mixtures. As in previous work, highly surface-active (nonreducible) colloidal agents are used so that both “positive” and “negative” maxima will be reduced by all the suppressors; and, therefore, Heyrovsky’s sign rule2 need not be considered. Neutral supporting electrolytes are employed throughout to (1) E. L. Colichman, THISJOURNAL, 72, 4036 (1950). (2) (a) J. Heyrovsky, “Actualites scientifiques e t induotrielles,” NO.90, Paris 1934, (b) J. Heyrovsky and M. Dillinger, Collcdion Csechoslov. Chcm. Commuws., 2, 626 (1930).
eliminate the effect of acidity. The three colloidal agents investigated here are: gelatin, lauryltrimethylammonium bromide and methyl cellulose (not previously studied). These represent3 typical cationic and non-ionic colloidal agents. Where possible, a study of the systems dealt with earlier has been extended into the alcohol region. Additional systems have also received attention so that the effect of valence, both in the ions of the reducible species and in the supporting electrolyte, might be observed. Experimental A Sargent-HeyrovsH Polaxograph, Model XII, equipped with a Sargent Circulator and Thermostat, S-181835 and S-84805, was used a t 25.00 rt 0.05’. The capillary passed 2.867 mg./sec. (open circuit), for an average drop time of 2.50 sec. in 0.50 A4 aqueous sodium nitrate, when under a pressure of 78.5 cm. of mercury. A drop time of 3.0 sec. was employed in all the maxima suppression experiments. The nitrogen gas was freed of oxygen by means of several vanadium-zinc amalgam wash bottles placed in series.* The oxygen free nitrogen was then passed through a sodium hydroxide solution and finally water and/or the concentration of alcohol under investigation before introducing the (3) The gelatin used here will act a s cationic material, see exptl. section of ref. 1 for justification. (4) L. Meites and T.Meites, Anal. Chem., 80, Q84 (1948).
Feb. 5, 1952
POLAROGRAPHIC MAXIMASUPPRESSION IN ALCOHOL-WATER MIXTURE
723
purified nitrogen into the cell. A mercury pool type electrolysis cell, Sargent S-29305, was used in all determinations. Baker C.P. and reagent grade chemicals were used without further purification. The commercial 95% ethanol was distilled once before use.
regard, it should be mentioned that all supporting electrolytes were maintained at 0.1 M to eliminate the influenceb of large ionic strength differences in comparing the results. Maxima due to organic species do not seem to show the orderly behavior Results and Discussion noted here with inorganic ions. Instead, for each The mercury pool cell used here can be and was given colloidal type maximum suppressor, the thoroughly cleaned between each determination. quantity necessary to suppress the maximum This type cell is superior to the H-cell used pre- varies considerably with each organic compound viouslyl for these investigations. Since i t is not investigated, even a t a fixed concentration of practical to change the agar plug between each reducible species. The M.S.P. of a given colloidal suppressor has determination, adsorption errors can influence the M.S.P. results when an H-cell is used even been found to vary directly in accordance with the though the cell is thoroughly rinsed with Blcohol concentration of the species being reduced. This and water between runs. Furthermore, the rela- direct concentration dependency (usually a t around tive El/, values obtained with the mercury pool 0.005 M and lower) has been noted for all the cell offer no disadvantage since these voltages are reducible species investigated here, with all the not pertinent to the maxima suppression investiga- colloidal maxima suppressors, and in all the solvent compositions. For example, the results in Fig. 2 tion, and thus are not cited. As discussed previously, the maximum sup- show that the M.S.P. of gelatin changes from 0.66 M to pression point (M.S.P.) of a given suppressor is X lO-*Y0 when cupric ion is 1.33 X when copper is changed to 4.00 X obtained by plotting values of '&/id (ratio of diffu- 2.00 X 10-zyO gion current a t maximum and when suppressed) 10-3 M. vs. log C. An extrapolation from the straight line relationship obtained, to where &,/id is unity, corresponds to complete suppression. The M.S.P.'s so obtained for the various neutral electrolyte systems in alcohol-water solutions are given in Table I. The variation of maximum suppression point with solvent composition is apparent. For a given dilute concentration of reducible ion, each solvent composition yields a definite M.S.P. seemingly irrespective of the nature of the ion being reduced or the supporting electrolyte. In this Fig. la
i'
Fig. l b
-0.2
-0.6 &.e. W. S.C.E., volt. Fig. 2a.-Effect of gelatin on 0.004 M CuCll in 0.1 M MgSO, in 25% alcohol, % X lo2: (a) 0; (b) 0.3; (c)O.6; (d) 1.0; (e) 1.5; (f) 2.0; (g) 3.0; (h) 4.0. f '/ita.
-0.2
-0.6 &.e VS. S.C.E., volt. Fig. 2b.-Effect of gelatin on 0.00133 MCuCll in 0.1 M MgSOd in 25% alcohol, % X lo*: (a) 0; (b) 0.30; (c) 0.66. f l / ~ m
.
It should not be inferred that all colloidal type suppressors will infallibly suppress all inorganic maxima according to the regularity noted in the results cited here. The surface process involved in -0.2 -0.6 -0.2 -0.6 suppressing maxima is undoubtedly much too Ed.0. VS. S.C.E., Volt. complex to allow such an all-inclusive generalization Fig. la.-Effect of lauryltrimethylammoniumbromide on to apply. Specific influences such as substantivitp 0.004 M CuClz in 0.1 M KCl in 25% alcohol, M X lo4: might well make a particular result anomalous. ( a ) 0; (b) 0.3; (c) 1.2; (d) 3.0;.(e) 6.0; (f) 10; ( g ) 20; For example, the results given in Fig. 1 show that a
f 1/100.
(5) The effect of ionic strength on polarographic properties has been
Fig. 1b.-Effect of lauryltrirnethylammonium bromide on studied recently by D. D. DeFord and D. L. Andersen, THISJOURNAL, 0.004 M CuClz in 0.1 M MgSO, in 25% alcohol, M X 104: 73, 3918 (1950). and shown to be an important consideration. (6) Recent results, E. L. Colichman, ibid., 78, 1795 (1951); ibid., (a) 0; (b) 0.3; (c) 0.6; (d) 1.2; (e) 2.0; ( f ) 4.0; (g) 10; 73,3385(1951),show the pronounced influence of substantivity on sur(h) 15; f %oo. face tension, interfacial tension and spectra,
EUGENE L. COLICHMAN
72.2
ir01*74
change in supporting electrolyte from magnesium sulfate to potassium chloride results in a system that is still suppressible a t the same M.S.P., but susceptible to reappearance of the maximum a t concentrations somewhat above the M.S.P. The
and gelatin increase linearly with increasing concentration of alcohol over the entire range investigated, 0 to 90%. On the other hand, lauryltrimethylammonium bromide’s M.S.P. values increase linearly up to about 30% alcohol and then suddenly increase markedly. This behavior is qualitatively analogous to the 4 variation found by Ralston and Hoerr.12 1,; 0 lYith increasing alcohol content of solvent, the critical micelle concentration of a related cationic-active salt, laurylammonium g. 9,0 j e thloride, was seen to undergo an abrupt w 3 change. In general, the increased solvent 3 power of alcohol for the hydrocarbon pori * i’ tion of any of the surface-active suppres3.0 sor molecules is antagonistic toward micelle formation. In the case of the quaternary ? ammonium salt, this antagonism results in a break in the linear M.S.P. relationship 25 0 50.0 75 0 above about 30% alcohol presumably due to a marked repression of ionic micelle yo Alcohol. Ionic formation in Fig. 3.-Effect of alcohol concentration on maxima suppression Of gelatin is points (M .S.P.): (a) methyl cellulose; (b) gelatin; (c) lauryltrimethyl- the and riot possible a t all in the case of ammonium bromide methyl cellulose. Possibly this is the fact that copper exists in the form of a negative reason why discontinuities in the M.S.P. values “chloro cupric ion” might well make its behavior are not found in these cases. in the presence of the strongly cationic-active TABLE I suppressor unique. The states of aggregation of the proteins in MAXIMASUPPRESSION POINTS(M.S.P.)” OF COLLOIDAL gelatin are undoubtedly altered by alcohol addiAGENTSIN ALCOHOL-WATER SOLUTION^ tions. These alterations are due to protein ioniza-Ah, %Reducible salt 0 25 50 90 tion differences as well as denaturation effects, Methyl cellulose (k X los) in The combining power of the protein fractions is thereby changed, and it is reasonable to expect MnC12 0.76 1.1 1.7 2.5 that the ability of gelatin to suppress polarographic cuc12 .70 1 . 2 1.8 2.6 maxima should be greatly influenced by the con2.8 CrdSOda .80 1 . 3 1.8 centration of alcohol present. Cr(N0& 1 . 3 1.9 2.9 On the basis of previous evidence cited,‘ it was Gelatin (% X lo2) in shown that the R1.S.P. values for a given colloidal 0.50 1 . 9 4 . 3 7.2 type maximum suppressor are comparable to their 0.53 2.0 4 . 5 7.0 “classical” critical micelle concentrations. It is, 2 . 3 5 . 1 7.8 however, erroneous to assume that all maxima sup8.0 4.8 pression involves micelle formation. For example, phenols which behave according to Hey- Lauryltrimethylammonium bromide ( MX lo3) in rovsky’s sign rule2 suppress maxima and are nonMnCL 0.21 2 . 0 15 colloidal. Even for strictly colloidal type supCUClZ 0.09 .20 n.s.’ 15 pressors, specific interaction abilities (e.g., the CrdSOh .09 .25 2 . 4 16 known7i8,9binding ability of proteins for both .20 2 . 5 16 Cr(NOda inorganic and organic ions) can complicate the a The M.S.P. value reported for each colloidal agent in micelle phenomenon. Thus for materials such as each alcohol-water mixture is an average value obtained by gelatin, maxima suppression may in part be due to investigating the following supporting electrolytes in each case. The 0.1 ,I1 supporting electrolytes were: KC1, reaction with the reducible species a t the mercury LiCl, &so4 and MgS04. Due t o solubility limitations drop surface or other adsorption phenomena. KCl and K~SOImere used only a t 0 and 25% alcohol, and The very small quantities of gelatin a t the M.S.P. MgSOa at 0, 25 and 50%. * The reducible ions responsible values preclude any possibility of interaction in the for the maxima are present a t 0.004 M. S o t suppressible “bulk” of the solutions as an explanation for the by cven extremely large concentrations. results. The linear relationships found between the maxIt is significant to note (Fig. 3) that the maxima suppression points (M.S.P.) of methyl cellulose ima suppression points (h5.S.P.) and increasing
-
‘ 2
2
.
.
(7) G Scatchard and b S Black, J . Phys. Collod Chem , 69, 88 (1949)
(8) I. M Klotz, c l a2 , THISJOURNAL, 68, 1488, 2299 (1946) (9) 1, 0 Longsworth and C F J a c o h e n , J Phy& Collord Chcm , 63, 128 (1940) (10) K Wiesner ColkcL~ouCzcchoslov Chon Comnruns , 12, 594
(1947) (11) R Kellin,
T H I 5 JOlfRVAL,
70, 1984 (1948)
s
3
(12) .4.W.Ralston and C. W. Hoerr, i b i d . , 68, 2460 (1946). (13) J. W. McBain and W. J. Jenkins, J . Chcm. Soc., 121, 232.5 !1922) (14) J. W. McBain and & E. I. McBain, Puoc. Roy. Soc. ( L o n d o i i ) , 1398, 26 (1933). (15) K.Hess and J. Gunderrnann, Bcv., ?OB,1800 (1937). (16) K . Hens, W. Philippoff and I T . Kiessig, Kolloid Z.,88, 10 (1939).
Feb. 5, 1952
REACTION OF DILUTEIODINE AND AMMONIA SOLUTIONS
alcohol concentration follow a general empirical equation, S = KIC K2AC,where
+
S = concentration of suppressor needed (M.S.P. value) A = concentration of ethanol in volrtme percentage
725
agents should prove helpful in choosing proper maxima suppressor concentrations, understanding their function, and ensuring their proper use in polarography.
C = concentration of reducible ionic species in molarity (must be dilute solutions, below about 5 X 10-8 M ) K , and Kz = constants characteristic of particular suppressor
TABLE I1 MAXIMASUPPRESSION CONSTANTS OF COLLOIDAL AGENTS IN ALCOHOL-WATER SOLUTIONS
A small value of K1 indicates that the suppressor functions a t low concentrations. The magnitude of K2 is indicative of the susceptibility to change of the M.S.P. values by increasing alcohol concentration. These values are given in Table I1 for the colloidal suppressors investigated here. Similar determinations for other useful colloidal
Methyl cellulose" 0.19 0 0054 Gelatin" 1.3 .19 Lauryltrimethylammonium bromideb 0.023' .0013c Based on concn. in percentage in empirical equation. Based on concn. in molarity in empirical equation. Value satisfactory up to about 30% alcohol. RECEIVED PORTLAND, OREGON JUNE 29, 1951
Colloidal agent
KI
Kz
[CONTRIBUTION FROM THE DEPARTMENT OF CHEMISTRY, UNIVERSITY OF MICHIGAN]
The Reaction of Dilute Iodine and Ammonia Solutions The decolorization of an iodine solution by ammonia a t relatively low pH cannot be accounted for in terms of hydrolysis to form H I 0 or the production of P\izH&. The reaction involved is readily reversible as shown by the ease with which the color decreases with increasing amounts of NH3 and increases on the addition of K I or NHdC1. Assuming that "21 is formed the net reaction would be 2"s 11Ft NHJ NH(+ I-. A series of 24 decolorization experiments involving varying amounts of 3 different NH&l-NHdOH solutions and five 0.01N KI3 solutions with differing amounts of K I were carried out. The data gave values for the equilibrium constant of this reaction ringing from 1.2 to 2.6, the average being 1.8. The precipitation of NzH& and the dissolving of this compound in excess of ammonia solution may be represented by the f 212 3NH8 = ?JT?H313 2NH4+ f 21- and K2H313 S H , = 3NH21. equations "21
+
+
+
+
At present, chemists generally regard this reaction as involving, first, the hydrolysis of the iodine in the somewhat alkaline solution to form HIO, and, second, the reaction of NH3 with the H I 0 to form nitrogen iodide, NzH313; followed later by slow conversion in part to iodate and iodide, and in part by decomposition. This idea of the primary reaction was expressed clearly by Seliwanovl confirmed by Chattaway, and retained by PartingThere have been occasional suggestions that and "12 might be intermediates in the formation of nitrogen iodide. Thus Cremer and Duncan4 wrote equations for the action of H I 0 on "1, giving "21 and NIBas successive products, and R ~ e d e r e rhaving ,~ obtained some evidence for the formation of NHzI in the reaction of dry NHa on I2 dissolved in cc&, noted the possibility that even in aqueous solutions "21 may be formed and then rearranged to give the nitrogen iodide. However, these suggestions appear to be simple speculations without experimental support. It is now possible to report direct experimental studies which make it appear very probable that the initial reaction between iodine and ammonia does involve the formation of iodamine, "21. These experiments are concerned mainly with the loss in color which occurs when standard amounts of iodine solutions are added to buffered solutions "21
(1) Th. Seliwanov, Bet., P7, 1012 (1894). (2) F. D. Chattaway and K. J. P. Orton. A m . Chem. J . , 24, 342 ( 1900). (3) J. R. Partington, "Textbook of Inorganic Chemistry," 6th ed., The Macmillan CO.,New York, N. Y., p. 627. (4) H. W. Cremer and D. R.Duncan, J . Chcm. Soc.. 2750 (1930). ( 5 ) E.Roederer, 2. a w p . &em. Chcm., Ye, 144 (1936).
+
+
containing varying amounts of NH&!l and of "*OH. This loss of color cannot be accounted for in terms of simple hydrolysis of the iodine in the somewhat alkaline solution to form HIO, nor can it be due to the formation of nitrogen iodide in solution. Two simple experiments are sufficient to justify this statement. First: when 50 ml. of 0.01 N KI3 solution is added to 200 ml. of 0.2 M Na2HP04no recognizable decolorization takes place, yet with 25 ml. of 5 N NH4OH present and sufficient NH4Cl to give the same PH as before, over 90% of the color is lost. Second: when 50 ml. of the 0.01 N K13 solution is added to 200 ml. of water containing only 1 ml. of 5 N NHIOH a moderate black precipitate forms within a few minutes, proving that nitrogen iodide is sufficiently insoluble to precipitate if it were being formed as a main product in this reaction. From the consideration of such experiments it was concluded that the soluble, colorless form of iodine is probably iodamine, "$1. The only alternative explanation would be to assume that ammonium hypoiodite is being formed as a very slightly ionized compound such that the hydrolysis of the iodine and the dissociation of the HLO, which normally take place very slightly under the conditions given, are actually being carried nearly to completion by the removal of the hypoiodite ion as the ammonium salt. Such an assumption is too highly improbable to warrant serious consideration. As additional support for the belief that NHzI is formed as the primary product in the reaction of dilute iodine and ammonia solutions the attempt was made to use the decolorization experiments as a basis for calculating an equilibrium constant for
