Iodine Monochloride End Point in Titration of Tripositive Antimony Titration with Iodate, Permanganate, and Ceric Solutions EDWARD W. HAJIRIOCI’\
KIOa Calcd. -111. 24.59
..
.
27.16 24 .59 27.16 24.59
2i:ia
Remarks SbOCl precipitate. Much I t formed, b u t oxidized slowly SbOCl precipitate. Much I t formed, but oxidized slowly Small SbOC1 precipitate Satisfactory titrations: care required t o avoid overrunning end point
26:64
...
27.16
...
... . ... ...
,,
Rapid and stable end points
... ,
.,
Less 1% a n d formed slowly. point stable
End
24:59
...
27.16 2k: k9 24:64 24.59
., ,
12
perceptible only after 1 min. Premature end point with I t color returning
Is appeared
5 to 7 min. after 90% of KIOI added No 1 2 until after several hours
1049
V O L U M E 20, NO. 11, N O V E M B E R 1 9 4 8 Table 11. Effect of Acid and of Chloride Concentrations on Titration of Tripositive Antimony with Permanganate (Iodine Monochloride End Point)
Expt. No. 1
2a 2b 3a 4a 4b 4c 4d 4e 4f
Final Formality Chloride HC1 1.0 1.5 1.5 2.0
k!%l$ 1.0 1.5 1.5 2.0
2.5
2.5
5
6a 6b 7a 7b 8 9a 9b 10a
0.025
0.05 0.10
0.15
4g
4h
Iodine Monochloride Added, hfillimoles 0.05 0.625 0.05 0.625
3.5
3.5
0.05 0.05 0.625 0.05 0.05
4.0
4.0
0.625
2.0
3.0
0.625
2.0
4 .O
0.625
2.8 3.0
2.8 3.0
KJInO4, M1.
Used 24.68 22.75 25.14 22.75 22.70 25.14 25.15 25.14 25.12 25.14 25.14 25.15 25.14 25.14 22.75 25.14 24.99 25.00 22.74
Calcd. 25.14 22.72 25.14 22.72
Remarks SbOCl precipitate Iz immediately on adding IC1. E n d points slow Iz oxidation slow
2k:i4
Satisfactorv titrations
22.72 22.67 22.70
22.72
... ... ... ...
... ... 2b:i4 22.72 25.14 25.14 22:72
:
22 i 2
1.25 millimoles Sb” added Satisfactory titrations IZreturns after apparent end point Premature end point 1 2 color later returns Iz color faint, titration not practical Iz color less t h a n with 2 F chloride Iz color returns after auparent end point. Unsatisfactory titration
monic half-cell in hydrochloric acid solutions becomes more oxidizing with increase of the acid concentration. Solutions 2.5 to 3.5 formal in hydrochloric acid are recommended for the above titrations. These limits are in essential agreement with the conclusions of Mutschin (6),from 1.8 to 3.6 normal, and lower than those of Jamieson (J), from 3.4 to 5.7 formal. I n order to distinguish between the effects of hydrogen and of chloride ion, t r o series of experiments were made. In one the concentration of acid was kept a t 2 formal and the chloride varied and in the second the chloride was kept a t 2 formal and the acid varied. These experiments showed that with increase of either hydrogen or chloride ion concentration the rate of oxidation of the antimony was decreased, although the hydrogen ion had the greater effect. As the ionic strength of the solutions was not kept constant, activity effects may be partly responsible for the observed results. Other experiments also indicated that when more iodine monochloride was added, unless the hydrochloric acid concentration was raised the oxidation of the iodine was noticeably slower. TITRATION WITH PERMANGANATE SOLUTIONS
monochloride added was in most case8 approximately equivalent to that formed in the iodate titrations. -4large number of experiments were made. Depending upon conditions, such as time required for the titration and quantity of antimony present, precipitates were likely to form in solutions that were less than 2 formal in hydrochloric acid. There was a pronounced tendency to overrun the equivalence point in solutions less than 3 formal in hydrochloric acid because of the sloiv oxidation of the iodine. When the hydrochloric acid concentration was 3 formal or greater, slow oxidation of the antimony caused premature end points unless great care was taken.
Because of these effects, satisfactory titrations demand such experience and patience that the use of the iodine monochloride end aoint wit,h ceric solutions is not recommended. Electrometric studies by Frank Rock of the titration of antimony by ceric sulfate with methyl orange as idicator have confirmed the conclusions of Rathburg (6) and Furman ( 2 ) that the oxidation of tripositive antimony by ceric solutions in the absence of iodine monochloride is much more rapid in 6 formal than in 2 formal hydrochloric acid; it therefore seems that in the above titrations, where the hydrochloric acid was 3 formal or greater, the iodine is preferentially oxidized by the ceric sulfate and that the sloiv oxidation of the antimony by iodine monochloride is the limiting factor. If this is true, the reported catalysis (9) by iodine monochloride of the oxidation of antimony by ceric solutions would seem to involve the iodine monochloride-iodine trichloride rather than the iodine-iodine monochloride couple. TEST ANALYSES
In order to determine the reproducibility of the resuks obtained by the use of the iodine monochloride end point and to compare the values so obtained with those resulting from the use of other methods, two series of comparison analyses were made (by E. \I-.Hammock).
The titrations were made by essentially the same procedure as were those with the iodate, except that, in order to reproduce the conditions existing a t the end point of the iodate titrations, in most cases an amount of iodine monochloride equal to that which would be formed in an iodate titration was added before the titration was begun. I t is seen from the data of Table I1 that the conditions under which a practical titration can be made with permanganate are essentially the same as those with iodate, except that the final hydrochloric acid should not exceed 3 formal. That this concentration should be different with permanganate than with iodate indicates that with increasing hydrochloric acid concentration the permanganate has a greater tendency than iodate for the selective oxidation of the iodine; this phenomenon is even more pronounced in titrations with ceric sulfate. Moderate variations in the amount of iodine monochloride and antimony did not cause marked changes in the characteristics of the titrations.
In the first series an antimonous solution rvas prepared by dissolving antimony trichloride in hydrochloric acid and diluting to give a solution approximately 0.05 formal in antimony trichloride and 3 formal in hydrochloric acid. At least three titrations of this solution were made by each of the following four methods: (1) Titration with permanganate using essentially the method of McSabb and Wagner ( 4 ) except that the solution was 2 formal in hydrochloric acid at the end point and \T as cooled to below 5 C. The end points were sharp and clear and lasted for from 30 to 40 seconds. (2) Titration with ceric sulfate using methyl orange as the indicator; the hydrochloric acid was adjusted to between 3 and 3.5 formal. (3) Titration with iodate, and (4) titration with permanganate, using the iodine monochloride end point. For these latter titrations 50-ml. portions of the antimony solution were taken, and iri all cases 5 ml. of carbon tetrachloride were used. Before the permanganate titration 5 ml. of 0.025 formal iodine monochloride were added. The final volumes varied between approximately 100 and 150 ml. and the final hydrochloric acid Concentration between approximately 2.5 and 3 formal. The maximum deviation of the individual titiations by each method was in all cases less than 1.5 parts per thousand, and the maximum deviation of the average values obtained by each of the methods !vas approximately 1 part pe1 thousand.
TITRATIONS WITH CERIC SULFATE SOLUTIONS
ASALYSIS OF AN ANTIMONOUS SULFIDE
The titrations were made essentially as were those with permanganate. As with the permanganate, the amount of iodine
Analyses were then made of an analyzed sample of “antimony ore” (obtained from Thorn Smith, chemist, no>-a1Oak, Mich.).
O
ANALYTICAL CHEMISTRY
1050 Table 111. Analysis of an Antimony Sulfide by Titration with Permanganate, Iodate, and Ceric Sulfate Run 1 2 3 AV.
Sb, %
0.10612N Permanganate,
M1. 43.30 43.33 43.30 43.31 27.95
0.10201N Iodate, M1. 45.10 45.12 45.12 45.11 27.96
0.09245N Ceric Sulfate, M1. 49.75 49.76 49.75 49.75 27.97
A private communication stated that the sample had been prepared by mixing a pure grade of "needle antimony" with anhydrous sodium sulfate; and that after being dried a t 100" C. for 1 hour and being analyzed by the method of 8.H. Low, it had been found to contain 27.85$& antimony. Samples of approximately 20 grams of the ore were dried a t 100' C. for 1 to 2 hours, weighed into 300-ml. conical flasks, and warmed slowly with 20 ml. of 6 formal hydrochloric acid until most of the hydrogen sulfide had been evolved. Then 100 ml. of 12 formal acid were added, a test-tube condenser was inserted in the flask, and the volume of the solution was reduced t F o thirds by evaporation. The resulting solutions were transferred to 1-liter volumetric flasks by means of equal volumes of water, then diluted to the calibration mark with 3 formal hydrochloric acid. Then 50-ml. portions of these solutions were titrated with iodate and permanganate to the iodine monochloride end point, and with ceric sul-
fate with methyl orange as indicator, using the titration procedures described previously. The results of these analyses are tabulated in Table 111. ACKNOWLEDGMENT
A considerable amount of the above experimental data was obtained as the result of a cooperative study by a section of honor students in a sophomore analytical chemistry course. The assistance of Norton Wilson in directing the work of this group and in collecting and interpreting the experimental results has been of great value. Preliminary studies were made by Robert Custer, Wyatt Lewis, and George Wald LITERATURE CITED
(1) Andrews, J . Am. Chem. SOC.,25, 756 (1903). (2) Furman, Ibid., 54, 4235 (1932). (3) Jamieson, J . I n d . Eng. Chem., 3, 250 (1911); "Volumetric Iodate (4)
Methods," New York, Chemical Catalog Co., 1926. McNabb and Wagner, IND.ENG. CHEM.,. ~ N A L . ED., 2,
251
(1930).
Mutschin, Z . ana2. Chem., 106, 1 (1936). (6) Rathburg, Ber., 61, 1663 (1928). (7) Swift, J . Am. Chem. SOC.,52, 894 (1930). (8) Swift and Gregory, Ibid., 52, 901 (1930). (9) Willard and Young, Ibid., 50, 1376 (1928).
(5)
R E C E I V E February D 24, 1948.
A lamp for Burning High-Boiling Petroleum Fractions Deter mi nut ion of Hydrogen S. G. HINDIN' AND A. V. GROSSE' Houdry Process Corporation, Marcus Hook, Pa. In lamp procedures previously developed for the determination of hydrogen, carbon, and sulfur in gasolines, the sample is burned in a lamp and the combustion products are collected and determined. A modified lamp design, which allows extension of the procedure to higher boiling petroleum fractions is described.
L
AMP procedures have been developed for determination of
hydrogen (9, 4 ) , carbon ( d ) ,and sulfur (1, 3 ) in low-boiling petroleum fractions and have been applied to analysis of other organic liquids. These procedures entail combustion of the sample a t the end of a wick; the oxidation products are recovered by suitable absorbents and determined. Khile eminently suitable for analysis of low-boiling liquids (below 260" C.), these lamp methods have not been applied to the analysis of higher-boiling materials. High-boiling liquids do not diffuse up the wick at a rate sufficient to ensure an adequate supply of liquid for combustion; performance of the Javes' lamp (3) has not been definitely established for such materials. A modified lamp design is indicated in Figure 1 which, by use of a variable hydraulic head, reduces the long wick path and permits the application of the lamp technique to high-boiling petroleum fractions (250" to 500" C.) and to other organic liquids in this boiling range. The burner is threaded with cotton wicks, three to five in number, which are trimmed flush with the top of the burner. Five to 10 ml. of sample are placed in the upper reservoir, and the lamp is weighed. The sample is then run into the lower reservoir and allowed to diffuseto the top of the wick. This step may take LO minutes or more. The lamp is then lighted with a microburner and inserted in the chimney, after which the determination is 1 Present addreea, American Sugar Refining Company, Research a n d Development Division, Philadelphia 48, Pa. Preeent address, Temple Univereity Research Institute, Philadelphia, Pa. f
carried on in the usual manner. After combustion, reweighing of the lamp indicates the amount of sample consumed. The dimensions of the lamp are not critical, the only restriction being that the over-all height and weight should be such as to permit weighing the lamp on an analytical balance. ACCURACY AND PRECISION OF DETERMINATION OF HYDROGEN
The accuracy and precision of the hydrogen determination in higher-boiling fractions are comparable to those obtained in gasoline analysis, as shown in Table I. In this table are indicated analyses for highly Durified hexadecane (cetane) and decahydronaphthalene (Decalin) and a130 for two wide fractions, together with the values that were obtained using the standard train procedure. Duplicate determinations on a large number of samples have Table I.
Accuracy and Precision Per Cent Hydrogen
Sample NO. 1 2 3
4
Description Cetane Deoalin 404-912O F. straight run cut 390-945O F. straight run cut
Theoretical 15.13 13.12
... ,.,
Lamp method 15.12 * 0 . 0 2 13.13 * 0 . 0 2
12.01 * 0 . 0 4 13.24
* 0.03
Carbonhydrogen train
...... ...... 12.07 * 0 . 0 4 13.20
* 0.08
