V O L U M E 2 3 , N O . 2, F E B R U A R Y 1 9 5 1 (2) Brann and Clapp, J . Am. Chem. SOC.,51, 39 (1929). (3) Carter and Williamson, Analyst, 70, 369 (1945). (4) Clippinger and Foulk, IND.ESG. CHEM.,ANAL.ED.. 11, 216
38 1 (7) Kolthoff and Pearson. I m . ENG. CHEM.,ANAL. ED., 4 , 147 (1932). (8) Wernimont and Hopkinson, I b d . , 15, 272 (1943).
(1939).
(5) Fieser, * J . Am. Chena. Soc., 46, 2639 (1924). (6) Foulk and Rawden, Ibid., 48,2045 (1926).
RECEIVED March 6 , 19.50. Presented a t the 115th Xfeeting of the CHEMICAL SOCIETY, Ssn Francisco. Calif.
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1
Tetrahydroxy Cobalt(l1) Ion as a Qualitative Test for Cobalt SAUL GORDON AND JAMES 31. SCHREYER University of Kentucky, Lexington, K y .
HEX a cobaltous salt solution is added to an excess of satuwrated sodium or potassium hydroxide solution, the cobaltous hydroxide that precipitates locally dissolves upon stirring to produce a deep blue solution which contains tetrahydroxy cobalt(I1) ion ( 5 ) . In the course of studying the spectrophotometric properties of this cobaltous complex in strongly alkaline solutions, the authors realized that the blue solution formed is specific enough to be utilized as a confirmatory test for the qualitative :inalysis for the cobaltous ion. The formation of this complex ion may he represented by the following equations:
+ 2 0 H - +Co(OH)z(Hz0)44 + 2HzO Co(OII)P(HzO)a+ 2 0 H - +Co(OH)4(HzO)n-- + 2H20 Co(H20)6++
1tt.icht.I (4)suggested the use of the slight solubility of cobaltous hydroxide in concentrated alkalies for the qualitative separation of sni:ill amounts of cobalt from nickel, the latter forming an insoluble hydroxide. Donath ( 2 )investigated some of the chemical properties of this complex, postulating the presence of a cobaltite ion, Coot--. Alvarez ( I ) reported that 1 drop of a 1% cobalt salt solution produces a pronounced blue color when added to a boiling solution of potassium or sodium carbonate. Qualitative rrayeiits used as tests for cobalt were reviewed by the International Commission for Reactions and Reagents ( 6 ) , but the application of this colored complex of cobalt was not reported. Although this reaction has been known for a long time, it has not been modified for adaptation to any scheme of cation analysis, nor have its 1iniitat.ions of detection and sensitivity been determined. EXPERLMENTAL
The schtmes most frequently used separate cobalt, nickel, and very often zinc, as a subgroup of the Group I11 cations. Therefore, Hogness and Johnson’s (5) method of analysis for the zinc subgroup was modified t o include this test for the detection of cobaltous ion. To determine the usefulness of this test, the Group 111 cations-aluminun, chromium, cobalt, iron, manganese, nickel, and zinc-Fvere determined in many combinations on a semimicro scale. The test solutions varied in concentration from 0.3 t o 50 mg. of the metal ions. Bfter dissolving the cobalt, nickel, and zinc sulfides in 1 ml. of 6 ,If hydrochloric acid and 1 ml. of 6 AT nitric acid, heat the mixture to boiling, and then transfer it to a casserole. With a stirring rod coalesce the sulfur formed, remove, and discard it, Then evaporate the solution to dryness. Dissolve the residue in a buffer solution of 1 ml. of 2 M sodium bisulfate and 2 ml. of saturated sodium sulfate solution. Divide this solution into two equal portions, A and B. To portion A add 5 drops of 3 M ammonium acetate, and pass hydrogen sulfide into the cold solution for a t least 1 minute Heat in a low flame, gradually raising the temperature almost to boiling. The appearance of a white or very light gray precipitate of zinc sulfide indicates the presence of zinc. Evaporate portion B of the buffer solution in a casserole, almost to dryness. Cool and add 6 drops of water, dissolving as much solid as possible. Label this solution C. Add 4 drops of solution C to 1.5 ml. of saturated sodium hydroxide solution in a 4-ml. test tube. The formation of a blue recipitate at the top of the solution indicates the presence of c o h t . Tap the t u b gently to allow the solutions and precipitate to mix.
Centrifuge. A blue supernatant, especially near the upper burface of the solution (and usually a blue-tinged precipitate) confirm the presence of cobalt. This blue test for cobalt is best seen if com ared with an equal amount of water against a white backgrounz To 1 or 2 drops of the buffer solution C, add 1 drop of 15 M ammonia solution, 4 drops of water, and 2 drops of dimethylglyoxime reagent. The formation of a red precipitate indicates the presence of nickel. DISCUSSION
Any white precipitate formed when the buffer solution is a d d d t o the saturated sodium hydroxide solution is sodium sulfate. light green precipitate yhich might appear a t t,his point is nickel hydroxide. The blue precipitate formed is either a basic cohaltous salt or white sodium sulfate colored by the cobaltous hydroxy complex ion. When the mixture R i centrifuged the blue complex solution is readily discernible. The absence of a blue solution or a blue-tinged precipitate indicates the absence of cobalt, nithin the limits of sensitivity of the test. The reactions that take place when the buffered solution is added t,o the saturated sodium hydroxide solution, assuming that cobalt, nickel, and zinc are present, may be represented by the following equations :
+
+ 2H20 (pink, Co(OH)t(H,O)a + 2015- --+ Co(OH)4(HzO)z-- + 2H10 (deep blue) CO(HZO)B-+ 2 0 H -
+
Ni(H20)6++ 2 0 H - +
+Co(OH)2(HzO)44
Si(OH)n(H20)r 4
+
Zn(Hz0)4++ 3 0 H - --+ H[Zn(OH)a]2Na+
+
2H20 (light green
+ 3Hz0 (colorless)
+ HSO4- + OH- -+- IVa&O, 4 + H2O (white)
This blue complex ion of cobalt may be formed in eit,her sat,urated sodium hydroxide or saturated potassium hydroxide solutions. The saturated sodium hydroxide solution is more satisfactory because of the higher hydroxyl ion concentration, which produces a deeper blue color with the cobaltous ion. If the test i3 applied t o a solution of cobalt without using the buffer solution, the sensitivity is about the same. The advantage of using the evaporated buffer solution is t’hat the white precipitate of sodium sulfate aids in the centrifugation of any other precipitate present and accentuates the blue color of the complex of cobalt. Although this method of cobaltous ion detection is suitable for use on both semimicro and macro scales, it is not satisfactory as a spot test. For most satisfactory results with this cobalt, test, the hydroxyl ion concentration must be greater than 12 M , which is not practical in spot test analyses. The test gave satisfactory results in the hands of a class of 126 in elementary qualitative analysis; 95.3 and 98.4’% of them reported successful tests on their known and unknown Group 111solutions, respectively. SENSITIVITY
The smallest amount of cobalt which may be detected is about 0.05 mg. in 1 drop of solution added to 1.5 ml. of saturated sodium
c
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ANALYTICAL CHEMISTRY
382 hydroxide solution This quantity is well within the amounts used in elementary qualitative analysis. In addition, it is found that 1 mg. of cobalt gives an excellent test in the presence of 15 mg. of nickel; 5 mg. of cobalt and 50 mg. of nickel cause the formation of a blue-tinged lightgreen precipitate xhen analyzed by the above procedure. In the cases of high concentrations of nickel as compared to cobalt, the test is best made by comparing the color of the precipitate with the color of nickel hydroxide free of cobalt, formed with the same reagents.
LITERATURE CITED
(1) Alvarez. E. P., Chern. News, 94, 306 (1906) (2) Donath, E., Z.anal. Chern., 40, 137-41 (1901). (3) Hogness, T. R., and W. C. Johnson, “Qualitative Analysis and Chemical Equilibrium,” 3rd ed., New Sork. Henry Holt and Co., 1947. (4) Reiohel, F., Z . anal. Claern., 19, 468-9 (1880) ( 5 ) Scholder, R., and Weber, H., %. anorg Chem., 216, 159-64 (1934). (6) Wenger, P., Duckert, K.,and Busset, 11.L., Hdv. Chim. Acta, 24, 657-70 (1941). RECEIVED July 19, 1950
Dark-Chamber Titrimeter for Chemiluminescent Indicator Titrations in Colored Solutions FREDERIC KENrVY AND R. B. KURTZ Hunter College, iVew Y o r k , .\. 1..
T H E instrument described obviates the use of a dark room in A titrations employing a chemiluminescent indicator. It can be used in a brightly lighted room. Ferrous solutions, highly colored with sufficient chromic ion to prevent the use of the usual redox indicators, were titrated with ceric sulfate, using siloxene indicator. I n the absence of chromic ion, the results were high by 1.3 parts per 1000. In the presence of 0.16 Mchromic ion, the error increased to 3.3 parts per 1OOO. When the indicator correction was applied this error was diminished t o 2.0 parts per 1000.
900
seo
840-
-6 a20 -
>’ soo5
DESIGN OF TITRIMETER
The instrument used, shown in section in Figure 1,is a lighttight box, A , with black interior walls, provided with a stirrer, C, a buret, B, and an opening, F , for observing the end point. The opening is so constructed that no light can pass into the box when the observer’s eyes are a t the opening. The stirrer may be eithermotordriven or hand-operated.
Table I.
z
0 760 -
a W E 740 --
IE
F
Titration
Deviation from Mean. hl1
7201
W
-A
‘ 0 f-
z w
mor
6601
Figure 1 . Dark-Chamber Ti trimeter
Volume of Ceric Solution Equivalent, to 30.00 M1. of Ferrous Solution at 23” A 2” C. Ceric Solution, M1.
-
780
c3
SILOXENE INDICATOR
The structure, preparation, and behavior of the siloxene indicator employed have been described ( 4 ) . The chemistry
-
a60
Potential Difference (from Curves), Mv.
Deviation from Mean,
640 --
I
600,
580
I
r
p
P
d /
MV.
2 2
VOLUME Mean
29.87
0.015
751
3
OF CERIC SOLUTION ML.
Figure 2. Titration Curves Used in Locating Soitchiometric Point
