CHEMISTRY O F I S D I C M .
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1235
COSTRIBUTIONS TO THE CHENISTRT OF I S D I U M . IV
THEEFFECTS O F C E R T A I X POLYHYDROXY ?;OS-ELECTROLYTES UPON PRECIPITATIOS OF HYDROUS TNDIVN HYDROXIDE
THE
THEItALD MOELLER .Voyes Chemical Laboratory, Unwerszty of Illanozs, Urbana, Illznoas Recezved M a y $4, 1941 IKTRODCCTIOS
The inhibitory effects exerted by polyhydroxy non-electrolytes such as the sugars and polyhydric alcohols upon the precipitation of metallic hydroxides have been the subjects of numerous investigations (1-5, 7-10, 13-23), and it has been shown that, if a sufficient quantity of the appropriate non-electrolyte be added to the metal salt solution prior to the addition of the base, the formation of any visible precipitate can in general be completely prevented. Such effects were originally ascribed t o the formation of complexes between the metal ion and the added non-electrolyte ( 5 , 7, 13), although Graham ( 5 ) also recognized the presence of colloidal oxide particlee. It is now believed, however, that in most instances the hydrous oxide or hydroxide is peptized by the excess hydroxyl ion fiom the added base in the presence of the polyhydroxy compounds (3, 9, 10, 14, 15, 17-21), for such solutions contain negatively charged colloidal particles (17, 21) and have the same conductivities as suspensions formed in the absence of the nonelectrolytes (2). On the other hand, evidence ha? been presented for complex formation in the cases of copper (22, 23), bismuth (8), and zirconium (1). S o detailed investigation of these effects as applied to indium has as yet appeared, although Gray (6) found his indium-cyanide plating bath to be stabilized by the addition of glucose, the effect of the sugar being to prevent the precipitation of indium hydroxide. Khilr Gray considered this inhibition to be due to the weakly acidic nature of glucose and the possible formation of a complex, others have felt that such is not the case (6, discussion a t end of paper). a further addition to the chemistry of indium, it wab decided to investigate the effects of bases upon indium sulfate solutions containing glucose, sucrose, levulose, or glycerol, both by the method of electionietric titration, a method which is often capable of demonstrating the exiitence or absence of complexes in solution, and by a conventional precipitation procedure. EXPERIM EYT 4 L
The source of indium ion in the experiments which follow was a solution 0.0501 M in indium sulfate, prepared from the pure anhydrous sulfate (11)
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THERALD MOELLER
and standardized by gravimetric determination of indium as the oxide. Tenth-normal solutions of sodium, potassium, and ammonium hydroxides were obtained by diluting strong carbonate-free solutions with carbon dioxide-free water. The sodium and potassium hydroxide solutions were standardized against the primary standard potassium acid phthalate and the ammonium hydroxide against standard N/10 hydrochloric acid. All bases were protected from carbon dioxide with soda lime. The organic chemicals,-levulose, d-glucose, sucrose, and glycero1,were of the best quality obtainable and were used without further purification. 14
I2 0 I LEVULOSE: I INw
IO 0 I O LEVULOX: I
IN**
0 I 0.
6
4
2
0
0
1.0
2.0 MOLS OH-
3.0
4.0
PER MOL IN+*+
Fro. 1. Titrations with eodium hydroxide in the presence of levulose
A . Electrometric titratwna, using the glass electrode For a given titration, 10 ml. of indium sulfate solution was pipetted into a beaker, the desired amount of a concentrated solution of the non-electrolyte added, and the whole diluted to 40 ml. The solution was then themostated to 25OC. f 0.5", stirred vigorously, and titrated at that temperature with one of the bases mentioned, the changes in pH during the addition of the base being followed with a Lee& and Northrup NO. 7661 Universal pH Indicator, the glass electrode of which had been calibrated against a M/20 potassium acid phthalate buffer. Results typical of those obtained are plotted in figures 1 to 4 for various mole ratios of non-electrolyte to indium ion as pH agrtinet the ratio of hy-
CHEMISTRY OF INDIUM.
1237
IV
14
12 e
I GLUCOSE : I
IN+++
10 9 10 GLUCOSE: I IN'".
8 I
a 6
4
2
0
0
1.0
2.0 MOLS OH-
3.0 PER
4.0
MOL IN+++
FIG. 2. Titrations with sodium hydroxide i n the preserxe of d-glucose 14
12 0
10
0 SUCROSE : I I
4
I SUCROSE: I IN"*
o
I O S U C R O S E : I IN*-
a I
a
6
4
2
0 0
I.o
2.0 MOLS
OH- P E R
3.0 MOL
4.0
INtt+
FIG.3. Titrations with sodium hydroxide i n the presence of sucrose
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THERALD YvIOELLER
droxyl ion added to indium ion initially present (12). Since the curves obtained for a given non-electrolyte were exactly similar regardless of the base added, only one plot is included for each of the non-electrolytes. Included in each figure is the curve for the titration of indium sulfate in the absence of the polyhydroxy compound (12). In each case the incidence of precipitation is designated by a dotted line. 14
I2
IO
8 I
n 6
4
2
0
0
1.0
20 MOLS OH-
30 PER
40
MOL IN+++
Fro.4. Titrations with potassium hydroxide in the presence of glycerol
MOLE BATIO OF XON-ELECTFCOLTTE TO INDIUY ION
Levulose
99.78 51.76 9.91
1
10 50
100
PER CENT INDIUM PBECIPITATED
-
d-Glumse
100.00 100.00 74.64
Sucrose
Glyoerol
100.00 99.78 92.17
100.00 100.00 100.00
I
B . Egects of polyhydroxy compounds u p o n the formation of filterable quantities of hydrous i n d i u m hydroxide The filterable indium hydroxide produced by the addition of ammonium hydroxide to indium sulfate solutions in the presence of varying amounts of each of these non-electrolytes was determined as follows: To duplicate
CHEJIISTRT O F Ih-DIUM.
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1239
10-ml. portions of the indium sulfate solution were added 30-ml. po~tions of solutions of the non-electrolytes of appropriate concentrations. -1bout 2.5 ml. of 6 S ammonium hydroxide was added to each, and, after standing 24 hr., the suspensions were decanted through filters. After being washed with cold water until sulfate-free, the residues nere converted to indium oxide and weighed. Typical results are given in table 1, where the per cent of indium has been determined by comparison of the amount of oxide obtained in the presence of the non-electrolyte with that produced in the absence of organic materials. In all instances except with glycerol and with very low concentrations of the others, extremely gelatinous, slocr 1y settling precipitates and opalescent filtrates were obtained, the degree of opalescence increasing with the amount of non-electrolyte used. Crlycerol had no apparent effect. Electrophoretic studies on these opalescent filtrates showed mass migration toward the anode, where flocculent indium hydroxide precipitated. Saturation of these sols with hydrogen sulfide converted them into yellow sols of indium sulfide, and boiling caused flocculation. DISCUSS105
The possibility of complex formation as an explanation for the hindering effect exerted upon the precipitation of hydrous indium hydroxide by the hydroxy compounds studied appears to be ruled out by the curves in figures 1 to 4. In all instances, regardless of the mole ratio of added non-electrolyte to indium ion initially present, precipitation began a t the same point (pH, 3.41; OH-/In++' = 0.85), and the curves coincide over the entire range except where the OH- to In+++ ratio exceeds 2.5 to 1, and particularly where this ratio becomes greater than 3 to 1. Such coincidence can only indicate that the same quantities of indium ion were present in the solutions after the addition of the polyhydroxy compounds as were present in the pure indium sulfate solution, and therefore that none of the indium ion is used in the formation of a complex with the non-electrolyte. In all cases, hydrous indium hydroxide was first precipitated. At ratios of hydroxyl ion to indium ion above 2.5, the curves show a greater or lesser divergence depending upon the nature and quantity of the non-electrolyte used and the amount of excess base added. In these regions, the flocculent precipitates first formed were in part peptized to negatively charged sols, except in the presence of glycerol where no peptization was noted. Inasmuch as peptization became more pronounced the greater the yuantity of non-electrolyte used, the decrease in p H a t a given OH-/In+-" ratio with increase in amount of polyhydroxy compound present can be
1240
TRERALD MOELLER
attributed to the removal of hydroxyl ions from the solution through peptization of the precipitates to negative sols. Some reduction in p H can also be ascribed to the weakly acidic natures of levulose and glucose, but the production of similar curves in the presence of sucrose seems to eliminate this factor in favor of the peptization hypothesis. Furthermore, all the data in the presence of glycerol (a weakly acidic material) fall along a common curve (figure 4) even a t a glycerol to indium ratio of 100 moles to 1, and it thus appears that hydroxyl-ion adsorption is not appreciable in the presence of this polyhydric alcohol (see also table 1). Since indium hydroxide shows no tendency to be peptized by hydroxyl ion in the region mentioned above in the absence of such polyhydroxy compounds (12), it appears that these data support the contentions of Sen (17,19) that such compounds by their own adsorption on the hydrous oxide particles prevent agglomeration and thereby permit enhanced hydroxyl-ion adsorption with resultant formation of a negative sol. Although the author feels that the possibility of any complex formation is precluded, it should be pointed out that Britton (I), from exactly similar curves for the titration of zirconium ion in the presence of glucose, accounted for the reduction in pH in the presence of the sugar through the production of some complex of unknown composition. The data in table 1 must be considered to be of only qualitative significance, because filtration may have caused some flocculation and because such gelatinous precipitates are hard to wash without further peptization occurring. However, the order of decreasing effectiveness in preventing the precipitation of indium hydroxide is levulose > d-glucose > sucrose > glycerol, the last having no effect. Although precipitates always formed under the conditions of concentration employed, the formation of any visible precipitate of hydrous indium hydroxide can be completely prevented by levulose, d-glucose, or sucrose if the amount added is sufficiently large. Glycerol is without effect, regardless of the quantity used. Sols produced in the presence of sugar concentrations far above those employed in this investigation are absolutely clear and contain negatively charged particles. Furthermore, they can be boiled without flocculating. Although it is obvious that the systems here investigated differ from Gray’s plating bath (6) and that the precipitation of the hydrous indium hydroxide occurs in a different fashion, it is to be noted that even a ratio of 50 moles of glucose to 1 mole of indium failed to prevent precipitation completely, whereas in the plating bath about 0.32 mole of glucose per mole of indium sufficed. In any case, however, complex formation appears extremely unlikely.
CHEMISTRY OF INDIUM.
IV
1241
SUMMARY
1. Indium sulfate solutions treated with extremely large amounts of levulose, d-glucose, or sucrose yield no precipitate when made alkaline but contain negatively charged particles of colloidal indium hydroxide. With lesser concentrations of these sugars, precipitates are produced which are in part peptized by the excess hydroxyl ion to negatively charged opalescent sols. Glycerol exerts no observable effect upon the precipitation of hydrous indium hydroxide. 2. Electrometric titrations in the presence of these polyhydroxy nonelectrolytes give no evidence of complex formation and point only to adsorption of hydroxyl ion by the precipitated indium hydroxide with consequent formation of a negative sol. 3. Determination of the filterable indium hydroxide produced in the presence of these compounds shows the order of decreasing effectiveneas in inhibition of precipitation to be levulose > d-glucose > sucrose > glycerol, glycerol having no effect. REFERENCES (1) BRITTON:J. Chem. Soc. 1926, 269. (2) CHATTERJIAND DEAR:Chem. News 12l, 253 (1920); Trans. Faraday SOC. 16, 122 (1921) (Supplement); Kolloid-Z. 18, 235 (1921). (3) DWMANSKII et al.: J. Rum. Phys. Chem. SOC.62, 729,747,1313, 1665, 1713,1879, 2249 (1930); J. Gen. Chem. (U.S.S.R.) 1, 209, 325 (1931). Biochem. Z. '27, 223 (1910). (4) FISCHER: (cr) GRAHAM: Phil. Trans. ill, 183 (1861); Ann. 121, 51 (1882); J. Chem. SOC. 16, 263 (1882). (6) GRAY:Trans. Electrochem. Soc. 66, 377 (1934). (7) GRIMAWX: Compt. rend. 08, 1485 (1884). (8)KUENAND PIRSCE:Kolloid-Z. 38 (Zsigmondy Festschrift), 310 (1925). (9) MEEIROTA AND SEN:J. Indian Chem. SOC. 4, 117 (1927). (10)MEEROTA AND SEN:Kolloid-Z. U , 35 (1927). (11) MOELLER: J. Am. Chem. SOC. 62, 2444 (1940). (12) MOELLER: J. Am. Chem. SOC.,89, 2625 (1941). (13) MULLER:Z. anorg. Chem. 43, 320 (1906). (14) NABAR, PATEL, AND DESAI:Kolloid-Z. 67, 173 (1931). (15) OSTWALD AND R~DIQER: Kolloid-Z. 49, 412 (1929). (16) PATEL AND DESAI:J. Indian Chem. SOC.7, 161 (1930). (17) SEN:J. Phys. Chem. 29, 1533 (1925). (18) SEN:J. Indian Chem. Soc. 4, 131 (1927). (19) SEN:Kolloid-Z. 43, 17 (1927). (20) SEN: Z. anorg. allgem. Chem. 174, 61 (1928). (21) SENAND DEAR:Kolloid-Z. 33, 193 (1923). (22) TRAUBE:Ber. MB, 3220 (1921); I B , 1899 (1922); MB, 1653 (1923), (23) TRAUBEAND GLAUBITT: Ber. 63B, 2094 (1930).
