769
V O L U M E 2 6 , NO. 4, A P R I L 1 9 5 4 strontium. In samples containing large amounts of barium, thp strontium sulfate contains a considerable concentration of liarium. A comparison of gravimetric and material balance values (Table V) shows that the latter are for the most part in better agreement with the theoretical and differ from it by no more than 0.4%, except in the strontium determination by the regular procedure. The error here is probably due to the inaccuracy of the spectrochemical determination of strontium when present in high concentration in the filtrate solids. Analyses of known mixtures in the matrix of chromic oxide gave low and erratic values for high concentrations of the alkaline earths. The material balance values themselves are slightly low. This is due in part to the uncertainty of the anion content of the precipitates which, for purposes of calculation, xere assumed to contain one anion only. I t will be seen that the material balance procedure gives satisfactory results even for the high gravimetric values obtained by single precipitations. These studies show that gravimetric results may be corrected spectrochemically to give close to theoretical percentages. This holds particularly for elements present in low concentrations
which as a rule coprecipitate wholly or in part with the major elements. The method has not been widely applied to work of this type but appears to have possibilities for further extension not only to studies of chemical procedures but to the complete analyses of minerals. Wider use of analyses of this type would lead to standardization of methods among laboratories and to the preparation of more reliable standards for spectrochemical work. LITERATURE CITED
(1) Hildebrand, 32. M , , and Lundell, G. E. F., “Applied Inorganic Analysis,” pp. 491-2, Xew York, John Wiley &- Sons, 1929. (2) Ibid., pp. 492-3. (3) Ibid., pp. 493, 503. (4) Hunter, R. G., and Headlee, A. J. W.,ANAL. CHEM.,22, 441-5 (1950). (5) Kallmann, S., Ibid., 20,449-51 (1948). (6) Rawson, S. G., J . SOC.Chem. Znd. (London),16, 113 (1897). (7) Skrabal, A., and Neustadtl, L., 2. anal. Chem., 44, 742 (1905). (8) Willard, H. H., and Goodspeed, E. W., IND.ENG.CHEY.,AKAL. ED.,8,414-18 (1936). RECEIVED for review June 15,1953. Accepted January 28, 1954. Presented before the Division of Analytical Chemistry at the 124th Meeting of the AMERICAN CF~EXICAL SOCIBTY, Chicago, Ill.
Volumetric Determination of Gallium ORVILLE W. ROLLINS,
U. S.
N a v a l Academy, Annapolis,
Md., and
CLAUDE K. DEISCHER, University of Pennsylvania, Philadelphia, Pa.
A
REVIEW of the literature has disclosed only one volumetric
method for the determination of gallium. Kirschman and Ramsey (3) were able to determine gallium by potentiometric titration with potassium ferrocyanide. Recently, Belcher, Kutten, and Stephen ( 1 ) have determined gallium by titration or with potassium ferrocq anide using 3,3’-dimethylnaphthidine 3,3’-dimethylnaphthidinesulfonic acid as indicator. The latter investigators titrated small amounts of gallium (0.74 to 2.94 mg.) with an average error of =k0.25’%. The authors have developed a volumetric method for the determination of this less familiar element using 8-quinolinol. Gallium is precipitated quantitatively over a considerable pH range with 8-quinolinol (8-hydroxyquinoline). Geilmann and Wrigge ( 2 ) have adapted the gallium derivative of 8-quinolinol to a gravimetric determination of the metal Sandell (8) has developed a fluorometric method for the determination of gallium using 8-quinolinol. This quantitative method is especially applicable to microgram quantities of the metal and has been L I S C ~ by Sandell in determination of gallium in silicate rocks. 1,acroix ( 5 )has extended the fluorometric method t o the determination of microgram (1.4 to 4.28) quantities of gallium in bauxite. Moeller and Cohen (6) have made use of 8-quinolinol in a spectrophotometric determination of gallium. The tripositive gallium is quantitatively extracted from an acetate-buffered (pH 3.0 to 6.2) salt solution with a chloroform solution of 8quinolinol. The resulting solution is analyzed with a spectrophotometer. Various metals such as zinc, iron. cobalt, nickel, copper, aluminum, and gallium are quantitatively precipitated with 8quinolinol. These precipitates can be used in the volumetric determination of the metals, since the 8-quinolinol can be readily brominated ( 4 ) . However, to date such a volumetric method has not been reported for gallium. Gallium is precipitated with 8-quinolinol according to the equation : Ga+++
+ 3CpH70N
4
+
Ga(CpHeON)3 3H+
The bromination of 8-quinolinol using potassium hromatepotassium bromide solution takes place as follows:
+ 5Bf + 6 H + 3 B r ~+ 3Hz0 CsH?ON + 2Rr2 CsHJ3r20K + 2 H + + 2Bf BrG3
+
+
REAGEYTS AND APP4RATUS
Gallium. The metal (2.8148 grams, 99.9% pure), obtained from the Aluminum Co. of America, East St. Louis, Mo., was dissolved in approximately 150 ml. of 6N nitric acid and diluted to 1 liter (pH 0.6). Potassium Bromate-Potassium Bromide. Approximately 2.79 grams of anhydrous potassium bromate, 24 grams of potassium bromide, and 2 grams of potassium hydroxide (all J. T. Baker’s c.P.) were dissolved in water and diluted to 1 liter. This solution should be stored in a borosilicate glass container. The solution (approximately 0.1N with respect to potassium bromate) was standardized as follows: Fifteen milliliters of concentrated hydrochloric acid was diluted to 150 ml., 4 grams of solid potassium iodide was added and allowed to dissolve, and to this solution a measured volume of potassium bromate-potassium bromide solution was added. By this procedure there is no loss of bromine from vaporization. The liberated iodine was titrated with sodium thiosulfate using starch as the indicator. The sodium thiosulfate was standardized against 0. lOOON potassium dichromate. 8-Quinolin01, J. T. Baker’s C.P. A 2.5y0 solution was prepared by dissolving 5 grams of the reagent in 200 ml. of 1.2X acetic acid (pH 3.74). Methyl Red, 0.1% solution in 95y0 ethyl alcohol. Sodium Hydroxide, 2N aqueous solution. Phenolphthalein, 1% solution in 95% ethyl alcohol. Starch, 2y0 aqueous solution. Apparatus. ,411 pH measurements were made using a Reckman pH meter, Model G. PROCEDURE
Pipet a sample of a solution containing tripositive gallium into a 250-ml. beaker and dilute to approximately 100 ml. After 1 drop of phenolphthalein indicator solution is introduced, add dilute sodium hydroxide until the solution turns red. While stirring this solution, a t room temperature, add a alight excess
770
ANALYTICAL CHEMISTRY DISCUSSION
Table I.
Analysis of Gallium Nitrate Solutions Gallium, Gram Taken Found 0.01407 0.01410 0.01407 0.01410 0.01970 0.01970 0.01970 0.01972 0.01970 0.01966 0.02815 0.02820 0.02815 0.02820
Error,
70
+0.21 +0.21 10.00 +o. 10 -0.20 + o 18 + O 18
I t is evident that gallium must be separated from those metals which are also precipitated with 8-quinolinol a t a pH of approximately 3.6. Prodinger ( 7 ) lists the different methods that may be used in separating gallium from other metals. From the above equations i t can be shown that the equivalent weight of gallium is l,lI2 the atomic weight. Then the total amount of gallium in a sample is given by the following:
MI. of KBr03 X .V of KBr03 X 1/12,000 X of the 8-quinolinol solution. The pH a t which complete precipitation occurs was found t o be 3.6. Cover the solution with a watch glass and heat on the steam bath for 1 hour. The initial precipitate is dense and flocculent; however, on heating this substance is transformed into fine crystals. Separate the precipitate by filtration using a sintered-glass crucible of fine porosity. Wash the precipitate thoroughly with distilled water. Dissolve the precipitate in 60 ml. of hot 1 . 5 5 hydrochloric acid and catch the resulting solution in the original beaker. Transfer this solution to a 500-ml. iodine flask, dilute to approximately 175 ml., add 4 to 6 drops of methyl red solution, and titrate slowly with standard potassium bromate-potassium bromide solution. The indicator is oxidized and thus becomes colorless with excess potassium bromate-potassium bromide solution. Add about a 5-ml. excess of this solution, swirl and stopper the flask, then add immediately, in small portions, 4 grams of potassium iodide in about 15 to 20 ml. of water. Add these samples to the well of the flask and admit by loosening the stopper. Finally rinse the well and the stopper with distilled water and titrate the liberated iodine with standard sodium thiosulfate solution using starch as indicator. Blank determinations by titration have proved to be negligible.
69.72
=
grams of gallium
Some representative results are shown in Table I. LITERATURE CITED
(1) Belcher, R., Nutten, A. J., and Stephen, W. I., J . Chem. Soc., 1952,2438-9. (2) Geilmann, W., and Wrigge, F. W., 2. anorg. allgem. Chem., 209, 129 (1932). (3) Kirschman, H. D., and Ramsey, J. B., J . Am. Chem. Soc., 50, 1632-5 (1928). (4) Kolthoff, I. M., and Sandell, E. B., “Textbook of Quantitative Inorganic z4nalysis,” p. 638, New York, hfacmillan Co., 1943 (5) Lacroix, S., Anal. Chim. Acta, 2, 167 (1948). (6) Moeller, T., and Cohen, A. J., ANAL.CHEM.,22, 686-90 (1950). (7) Prodinger, W., “Organic Reagents Used in Quantitative Inorganic Analysis,” pp. 79, 179, New York, Elsevier Publishing Co., 1940. (8) Sandell, E. B., IND.ENG.CHEM.,ASAL. ED., 13, 844-5 (1941); ANAL. CHEM., 19,63-5 (1947). ~~
RECEIVED for review August 14, 1953. Accepted January 2 5 , 1954.
Titrations in Nonaqueous Solutions BENJAMIN R. WARNER and WESTON W. HASKELL Chemistry Department, Duke University, Durham, N. C.
I
N T H E course of work being carried out on tobacco smoke, it
in a U-tube separated the solution being titrated from the beaker
became desirable to determine the total amounts of titratable acids and bases, both strong and weak. The ASTX method ( 1 ) using organic solvents and the calomel-glass electrodes system was found to be inapplicable to the materials encount’ered in this work.
or saturated potassium chloride solution into which the siphon of
a calomel half-cell dipped, in a chloranil-calomel electrode combination. Fritz (3) describes the use of a silver-silver chloride electrode in place of the calomel half-cell to eliminate the liquid junction difficulties. The advantages of the titration cell de-
GLASS ELECTRODES WITH GLACIAL: ACETIC ACID LIQUID JUNCTION
I n the last few years, the method of Conant and Hall ( 2 , 6) for titrating weak bases in glacial acetic acid with perchloric acid i n glitc.isl acetic has been greatly improved. Recently, Pifer, \v‘ollish, and Schmall (6) described a titration cell using the Beckman No. 1170 fiber-type calomel electrode and glass electrode. I n the authors’ experience using the Beckman S o . 270 fiber-type calomel electrode, the quantities of the order of 2 mg. of weak bases, such as aniline and pyridine, could not be titrated successfully with the solvents and titrants described. The potentials were not steady and the end points were not reproducible. The difficulty seemed to be caused by the liquid junction potential which changed as the potassium chloride solution flowed from around the calomel electrode into the solution being titrated. This difficulty was obviated by the use of a glacial acetic acid bridge, separated from the solution being titrated by a fine sintered-glass disk, into which the calomel electrode could dip. The potential of this liquid junction does not change in a manner that interferes with the potential changes due to the neutralization of the base being titrated. The titration cell is easily cleaned (with solvents such as acetone) and a new junction can be made Kith fresh glacial acetic acid for each titration. This type of liquid junctionis asimplificationof that used by Halland Conant(5) in which a, supersaturated solution of lithium chloride in acetic acid
i----Calomel
Saturated Pot a ssi u rn
Electrode
rl” h
/+ 30mm-l Figure 1. Titration Cell with Glacial Acetic Acid Liquid Junction
