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
771
V O L U M E 26, NO. 4, A P R I L 1 9 5 4
does not respond to changes in basicity. The antimony electrode (Figure 3) was prepared in the following manner:
A 9-mm. borosilicate glass tube was sealed a t one end and successive portions of antimony metal powder (General Chemical Co.) were melted in it so that a solid rod of antimony about 30 mm. in length was formed in the glass tube. The end of the glass tube was then ground off on a wet belt sander to leave a 12-mm. length of antimony exposed. Electrical connection was then made by soldering a copper wire to the electrode (see Figure 3). It was found that only by removing the oxide coating from the electrode surface with sand paper before a titration would the electrode function properly or a t all. When this was done reproducible potentials and end points were obtained. Another factor that must be regarded is t h a t the end point potential in the titration of phenols is slowly reached. For this reason, it is necessary to wait until the potential is really constant before making a reading. I t is also necessary to use freshly distilled butylamine in the titrations if a high blank titration is to be avoided. Figure 4 illustrates the titration of thymol with sodium methylate in 10% methanol-benzene (volume/volume) as titrant and butylamine as solvent.
I 820Titrant -0005N * C I 0 4 In 50 5 0 ( V / V : G l a c i o l
1
Plus Om1 Cvclohexane
- - 11 500
I.
0
1
1020-l
~
4
8
I2
20
16
24
M L 0 0 0 5 N HCIO,
Figure 2.
940
-
Titration of Pyridine 860--
scribed in this paper are that commercial rugged type electrodes can be used, excessive leakage of potassium chloride solution from the calomel electrode does not interfere, and that leakage of acetic acid into the solution being titrated has little or no effect since acetic acid is the solvent.
Apparatus. The cell and the electrode arrangement are shown in Figure 1. A Beckman No. 290 glass electrode and a Beckman No. 270 calomel electrode were used in conjunction with the Beckman Model G pH meter for determining the potentials. Stirring was accomplished with a Precision Scientific Co. MagMix. An iron bar enclosed in a 15 X 3 mm. borosilicate glass tube served as a stirring bar. The p H meter, the Mag-Mix case, and the glass electrode holder were grounded. Procedure. The samples were dissolved in 15 ml. of glacial acetic acid and placed in the titration vessel. Titrations were carried out with 0.005N perchloric acid in glacial acetic acid. Better end points were obtained by using 5 ml. of cyclohexane and 10 ml. of glacial acetic acid as the solvent, although the potential readings were less steady in the initial stages of the titration. rl 5-ml. microburet (Scientific Glass Co. Catalog No. b12935) was used with potential readings taken every 0.1 ml. The easily determined end point potential ob--Copper W i r e tained in the titration of 0.5 mg. of pyridine in cyclohexane glacial acetic acid is shown in Figure 2.
780
Butylamine
8 - 108mg Thymolt 15ml B u l v l o m i n e
___
3004 0
1
2
3
4
5
6
7
M L 0 0 2 8 2 M SODIUM M E T H Y L A T E
Figure 4.
Titration of Thymol
By using these titration cells and exercising the precautions described, the quantities in tobacco smoke of acids and bases with dissociation constants of the order of 10-6 as differentiated from the quantities of acids and bases with dissociation constants the order of have been determined.
ANTIMONY ELECTRODE
ACKYOW LEDGhI ErvT
Fritz and Lisicki ( 4 ) reported I lie successful titration of weak acids such as phenols using an antimony-glass electrode cell with b u t y l a m i n e a s solvent. The authors’ results with this method have been equally good. However, they have found that the antimony electrode behaved erratically and sometimes did not function a t all unless the electrode surface was renewed prior to each tit,ration. Evidently, an inactive film is formed on t h p antimony, 80 that the electrode
The titration ccll \vas comtructrd k ) ) ~ J . D. Graham, Jr., Duke University.
--__ 9mm
Pyrex Tubing
LITERATURE CITED
(1) Am. SOC. Testing Materials, Designation D 664-46T, Am. Soo. Testing Materials Standards, Part 111-A, pp. 824-32, 1946. (2) Conant, J. B., and Hall, N. F.. J . Am. Chem. SOC.,49, 3062 (1927). (3) Frftz, J. s., A N A L . CHEM.. 22, 1028 (1950). (4) Fritz, J. S., and Lisicki, N. M., Ibid., 23, 589 (1951). (5) Hall, N. F , and Conant, J. B., J . Am. Chem. S O C . ,49, 3047
Antimony
Figure 3. Antimony Electrode for ~ i lion of Weak Acids
(1927).
(6) Pifer, C. K., IVnlliph, E. C . , and Brhmall, AI., ANAL.CHEM.,25, 310 (1953).
~ ~ R E C E ~~ V P Dfor review August 17. 1953. 4 c r ~ p t e dJanuary 16, 1954. Rupported in part by a grant from the Damon Runyon Fund.
Work
