794
THERALD MOELLER
CONTRIBUTIONS TO T H E CHEMISTRY OF INDIUM. VI'
THEEFFECTSOF CERTAINHYDROXY ANIONSUPON THE PRECIPITATION OF HYDROUS INDIUM HYDROXIDE THERALD MOELLER
Noyes Chemical Laboratory, University of Illinois, Urbana, Illinois Received May 80, 1048 INTRODUCTION
That the precipitation of many hydrous metallic oxides and hydroxides from corresponding salt solutions can be effectively inhibited by the addition of citrate, tartrate, malate, or other related hydroxy anions is well known, since the literature contains numerous accounts of studies undertaken in attempts to explain such phenomena. To account for these effects, it is generally conceded that complex formation takes place between the metallic cation and the hydroxy anion (probably in a manner involving the hydroxy group or groups) with a resultant reduction of cation concentration below the liminal level necessary to effect precipitation, although in certain instances peptization apparently occurs as a result of the presence of the organic anion and leads to the production of negative sols (3, 5, 12). Although the failure of hydrous indium hydroxide to precipitate in the presence of tartrate was noted shortly after the discovery of the element (6,19, 20), neither the nature of the solutions thus produced nor the cause of the effect has received attention. The only related literature reference appears to be one indicating that indium chloride solutions in the presence of citrate can be adjusted to pH 7.2-7.4 without precipitation (22). Inasmuch as the electrometric titration technique which has recently been employed in studies upon some of the characteristics of hydrous indium hydroxide (8,9) has in the past yielded information relative to the behaviors of a number of metallic salt solutions when'treated with alkali in the presence of hydroxy anions (1,2,10 to 14), it was deemed worthy of application to similar systems containing an indium salt. EXPERIMENTAL
The source of hydrated indium ion was a solution 0.0500 M in indium sulfate (8, 9). Tenth-normal sodium and potassium hydroxides and sulfuric acid, prepared and standardized by the usual methods, were the titrating agents. Sodium and potassium citrates and tartrates were of analytical reagent quality and were used without further purification. Sodium and potassium malates were prepared by neutralization of C.P. dl-malic acid with the corresponding alkalis, evaporation, and recrystallization. The M / 5 solution of sodium lactate was obtained by neutralization of the C.P. acid and dilution. 1
For the fifth paper in this series see Moeller: J. Am. Chem. SOC. 64, 953 (1942).
14
12
IO
8
r
a 6
4
2
0
FIG.
14
12 0 0
R X O
0
‘1.0
=a
IO
8
I 0.
6
4
2
0
1.0 2.0 3.0 4D MOLES OH- PER MOLE IN+++ FIG.4. Titrations with aodium hydroxide in the pnrsenca of sodium lwtate 786
0
CHEMISTRY O F INDIUIM. V I
797
A . A l k a l i titration procedure Titrations were made a t 25OC. =t0.5"on solutions containing 10 ml. of indium sulfate solution and varying quantities of the hydroxy salts in total volumes of 40 ml. according to the method previously described (9), except that changes in pH ivere followed xith the glass electrode of a Beckman Laboratory Model pH Plleter.
FIG.5 . Titrations with potassium hydroside and sulfuric acid
Results typical of those obtained are plotted in figures 1 to 4 as pH against the mole ratio of added hydroxyl ion to indium ion initially present a t varying mole ratios ( R ) of added hydroxy salt to indium ion taken. Because of the exact parallel betMeen results for sodium and potassium compounds, data for but a single alkali are given in each plot. Included in each figure, for purposes of comparison, is the titration curve for indium sulfate alone (Le., R = 0); where precipitates formed, the incidence of precipitation is indicated by vertical arrows.
798
THERALD hlOELLER
R . Alkali-acid tztrations Titration with alkali was in some instances followed by immediate back titration with sulfuric acid. Results obtained in this fashion in the presence of potassium citrate, tartrate, and malate a t R = 1.0 are given in figure 5. DISCUSSION
Of the hydroxy anions investigated, only the lactate proved to be incapable of preventing the precipitation of hydrous indium hydroxide upou the addition of alkali. With citrate, tartrate, and malate, however, hydroxide formation was completely inhibited at R d u e s equal to or exceeding 1.0, although alkali tartrate alone often yielded alkali-soluble precipitates. Differencesbetween the behaviours of lactate and the other anions are apparent from a comparison of figure 4 with figures 1 to 3,the lack of influence of the Iactate being indicated by the similarities of the titration curves in its presence and absence. The other anions, however, profoundly affect the course of the titrations. As is shown in figure 1, the presence of 1 or more moles of citrate per mole oi indium ion gives a marked break in the titration curve a t an OH- to In+++ratio of 1.25. This may be taken as indicating that the interaction of citiate and hydrated indium ions releases titratable hydronium ion to the extent of 1.25 moles per mole of indium, the break in the titration curve then correqponding to the neutralization of this acid. The abruptness of the break when R = 1.0, as compared vith the less pronounced inflections at higher R values, is undoubtedly due to the indium and citrate ions being present in the exact stoichiometric quantities necessary for interaction, the effects of any liberated hydronium ion then being unmasked by the hydrolytic reactions of excess citrate. At larger R values, R leveling effect due to the buffer action of the citrate is apparent. In the plateau regions following neutralization of the liberated acid, hydroxylion absorption again occurs, and this may be regarded as a reaction of hydroxyl ion with those valences of indium not firmly bound into the initial complex with the resultant formation in solution of increasingly basic citrate-indium complexes (see references 10 to 14 for similar considerations). Coincidence of the curves at an OH- to In+++ ratio of approximately 2.5 marks the completion of these reactions, and the remainder of each titration proceeds, except in a lesser pH interval, as with indium sulfate alone (8). The results with tartrate and malate are indicated by figures 2 and 3 to be exactly similar, although the initial inflection with tartrate is less abrupt and with malate scarcely apparent. Although difficult of exact determination nith the malate, these breaks correspond to the liberation of 1.5 moles of hydronium ion per mole of hydrated indium ion and are again most noticeable v hen R = 1.0. Complex formation thus involves but a *ingle mole of the hydrosy anion per mole of indium, biit the malate complex is much leFs well defined and htable. Addition of more alkali again results in soluble basic complexes.
799
CHEMISTRY OF INDIUM. V I
Further evidence for the liberation of hydronium ion as a result of the interaction of indium and hydroxy ions is presented in table 1, where the pH values of indium sulfate solutions treated with varying quantities of 0.1083 A; tartaric acid are compared with those of solutions containing the same quant,ities of tartaric acid alone in the same total volumes. The mixed solutions yield markedly higher hydronium-ion concentrations. Citric acid gave similar results. hlthougli the formation of hydronium ion has been reported in a number of other metallic cation-hydroxy anion systems (1, 10 to 14, 18, 23), proposed attempts at explanation differ. Thus, while Brit,ton ( 1 ) and later Morton (13) have believed that salt formation between the cation and the hydroxy anion is followed by hydrolytic reactions releasing the free hydroxy acid, other investigators (4,15, 16, 17,21) indicate that the hydroxy groups are involved. The nonprecipitation of hydrous oxides and hydroxides from such solutions lends support to the latter view. Even though the indium ion is effectively converted into a complex, equilibria must exist between traces of hydrated indium ion and the basic complexes formed TABLE 1 h'flect o,f indium sulfate upon the p H of tartaric acid solutions I A R I A K I C ACID IN 40 IUL.
I
PH Tartaric acid alone
I
Indium sulfate plus tartaric acid
ml.
0 5
10 15
20
2.67 2.55 2.45 2.40
2.65 2.40 2.30 2.20 2.10
800
THERALD MOELLER SUMMARY
1. Indium sulfate solutions treated with equimolar (or greater) quantities of alkali citrate, tartrate, or malate yield no precipitate when titrated with alkali hydroxide, although excessive quantities of t,he latter may effrct prcripitation. Alkali lactate does not inhibit hydroxide formation. 2. Electrometric titration data indicate the release of hydronium ion to the extent of 1.25, 1.50, and 1.50moles per mole of indium ion for citrate, tartrate, and malate solutions, respectively. 3. Reaction of indium-hydroxy anion solutions with alkali involves, in order, neutralization of liberated hydronium ion and basic complex formation. 4. The reaction of indium and hydroxy ions is considered to occur at equimolecular ratios and to involve the hydroxy groups of the organic radicals. REFEREKCES (1) BRITTON:J. Chem. SOC. 1986, 269. (2) BRITTONAND BATTRICK: J. Chem. Soc. 1934, 196.
el al.: J. Russ. Phys. Chem. SOC.61,747,1313,1665(1930);Hull. sac. chim. (3) DUYANSKII 41, 1211 (1930);49, 132 (1931);J. Gen. Chem. (U. S. S. R.) 1, 325 (1931). (4) GOVELA N D VAISHYA:J. Indian Chem. SOC.12, 193 (1935). Science Repts. T6hoku Imp. Univ. 16, 825, 841 (1927). (5) HAKOMORI: (6) MEYER:Ann. 160, 137 (1869). (7) MOELLER:J. Am. Chem. Sac. 64,2444 (1940). (8) MOELLER:J. Am. Chem. SOC.69,2625 (1941). (9) MOELLER:J. Phys. Chem. 46,1235 (1941). (10) MORTON: Quart. J. Pharm. Pharmacol. 5, 561 (1930). (11)MORTON:Quart, J. Pharm. Pharmacal, 4, 1 (1931). (12)MORTON:Quart. J. Pharm. Pharmacal. 4, 161 (1931). (13)MORTON:Quart. J. Pharm. Pharmacal. 4,451 (1931). (14)?vfoRToN: Trans. Faraday sac. 48, 84 (1932). (15)PARISELLE:Compt. rend. 166, 130 (1927). A N D DELSAL:Compt. rend. 198, 83 (1934). (16)PARISELLE (17)PARISELLE: Compt. rend. 202, 1173 (1936). (18) PAVLINOVA: J. Applied Chem. (U.S.S.R.) 9, 1682 (1936);10, 732 (1937);Acta Univ. Voronegiensis (U.S.S.R.) 11 121, 7, 15 (1939). (19)REICHAND RICHTER:J. prakt. Chem. 90, 172 (1863). (20) REICHAND RICHTER:J. prakt. Chem. 98, 480 (1864). (21) REIHLENA N D HEZEL:Ann. 487,213 (1931). (n) VOX OETTINGEN: Proc. Sac. Exptl. Biol. hled. 29, 1188 (1932). (23) ZOLOLUKHIN: Acta Univ. Voronegiensis (U.S.S.R.) 11 [2],19,27 (1939).
