Estimation of Bromides in the Presence of Other Halides P. L. KAPUR, M. R. VERMA, AND B. D. KHOSLA, University Chemical Laboratories, Lahore, India
E
TABLE111. DETERMINATION OF BROMIDES IN PRESENCE OF CHLORIDE
STIMATION of bromides in the presence of other halides is a problem of importance and a number of papers on the subject have been published.
Bromides in Presence of Chlorides Most of th? published methods can be classified under two
2.0
1.0 5.0
1.0 1.0
-
of N a A O *
12.45 16.95
0.001602 0.0005902
42.35 16.65 8.25
Stren t h
0.0005902 0.0001200 0.0001200
Weight of KBr in 100 M1. Found Present
Gram
Qram
0,996 1.000 0.4997 0,1990 0.0990
1.0000 1.0000 0.6000 0.2000 0.1000
To effect oxidation Baubigny and Rivals (I) used a mixture of copper sulfate and potassium permanganate, Clausmann (8) used a mixture of chromic and sulfuric acids, Baughman and Skinner (8) used chromic acid in concentrated solutions, Meloche and Willard (7) used potassium permanganate and hydrochloric acid, and Edwards, Nanji, and Parkes (6) used potassium permanganate and dilute phosphoric acid. These methods require distilling the bromide mixture with the oxidizing agent and collecting the liberated bromine in a vessel containing potassium iodide solutions, when an equivalent amount of iodine is liberated which can be estimated volumetrically by titrating against standard thiosulfate solution. There are other methods where bromine produced by oxidizing agents is extracted with carbon tetrachloride (9, fO),which is separated and shaken with potassium iodide. Iodine thus liberated is determined volumetrically. DenoeI (4) has recently described an extraction method for the estimation of bromides in the presence of chIorides, using potassium bromate as the oxidizing agent.
TABLE 11. BLANKEXPERIMENTS WITH SODIUhf CHLORlDE ALONE
Sodium Chloride Present
MU. 25 50
75
100 150
2.0 2.0 2.0
0.025
Gram 0.050 0.075 0.100 0.125 0.150
-
~~~~~, I2
2Br M1.
11.12 11.12 11.12 11.15 11.20 11.30
Strength of Na2S203 used, 1 ml.
TABLEI. DETERMINATION OF BROMIDES NazSzOs Required, Iz 2Br M1.
NaCl Added
2.0 2.0 2.0
general heads: (1) those depending upon the choice of certain oxidizing agents by which bromine alone is liberated and distilled off, the chloride remaining in the residue as chloride, after which bromine collected is determined iodometrically, gravimetrically as silver bromide, or colorimetrically by means of fluorescein solution or fuchsin-sulfuric acid reagent; and (2) those depending upon the quantitative oxidation of bromides to bromates either by chlorine water in the presence of sodium bicarbonate (11) or by the addition of the theoretical amount of hypochlorite in the presence of borate buffer and sodium chloride to half saturation (5, 8). If chloride be present a small amount of chlorate is invariably formed and this must be allowed for b y using controls subjected to the same procedure from the start; if iodide be present, it is quantitatively oxidized to iodate and then the apparent bromide figure includes the iodide.
KBr S o h tion Taken MI.
KBr Solution Taken MI.
Sodium Thiosulfate Used M1. Nil Nil Nil 0.03 0.18
I n the present investigation the authors used mixtures of nitric and chromic acids as oxidizing agents and removed the liberated bromine b y shaking the mixtures with carbon tetrachloride. 157
=
KBr in 100 M1. of Solution Found Present
Qrama
Qrama
1.0008 1.0008 1.0008 1.0035 1.0080 1.0170
1.0004 1.0004 1.0004 1.0004 1.0004 1.0004
0.0018 gram of KBr
REAGENTS.A 1 per cent stock solution of potassium bromide was made from analytical reagent potassium bromide. Different volumes of this solution were taken to estimate the bromide content. Carbon tetrachloride available in the stores was purified according t o the standard methods (12). Sitric acid and chromic acid were extra pure Merck quality. PROCEDURE. A known volume of potassium bromide solution was mixed with an excess of 10 per cent chromic acid and an equal volume of concentrated nitric acid in a 100-ml. separating funnel. The mixture was shaken with 10 ml. of carbon tetrachloride. The lower layer of carbon tetrachloride containing the liberated bromine vas separated. To ensure complete removal of bromine, the solution was further shaken a number of times with successive 5-ml. portions of carbon tetrachloride and the latter was separated. It was found that chromic acid dissolves to a small extent in carbon tetrachloride and interferes later on with the estimations. Therefore, carbon tetrachloride extractions were shaken Kith water to remove any chromic acid present. To safeguard against any loss of bromine, the water layer was again shaken with a fresh 5-ml. portion of carbon tetrachloride and this extraction added to the rest of the extractions. To the carbon tetrachloride extractions in a glass-stoppered Erlenmeyer flask potassium iodide was added and the equivalent amount of iodine liberated was titrated against standard sodium thiosulfate. The end point is indicated by the disappearance of violet color from the carbon tetrachloride.
TABLE IV. EFFECT OF IODIDES Potassium Iodide Present
Sodium Thiosulfate Used
MQ. 25 30 40 75
Nil Nil Nil Nil
I n Table I are given the results obtained on a specimen of pure potassium bromide, showing experimental results in very good agreement with the calculated ones. I n all these cases 10 ml. of 10 per cent chromic acid and 10 ml. of nitric acid were used for oxidation. Carbon tetrachloride extraction was done four times. As may be seen from Table I, very small amounts of bromides, like 0.001 gram in 1.0 ml. of 0.1 per cent solution, can be easily and accurately estimated. A preliminary series of blank determinations was carried out to ascertain the effect of chromic acid-nitric acid mixture on varying concentrations of chloride. The figures in Table I1 show that no iodine is liberated from carbon tetrachloride extractions on the addition of potassium iodide when the concentration of chloride is not very high. I n Table 111are recorded results of determination of potassium bromide in the presence of varying quantities of sodium chloride.
158
INDUSTRIAL AND ENGINEERING CHEMISTRY
It is clear that if the amount of chloride present be not large, the amount of bromide found is almost theoretical. High results in the presence of much chloride have been noted by other investigators (9). Bromides i n Presence of Iodides The interference of iodides in the oxidation method of determining bromides is overcome by oxidizing the iodide to iodate (7). The authors have observed that the method described above, when slightly modified, overcomes the interference of iodides, as they are completely oxidized to iodates b y the excess of nitric acid-chromic acid mixture.
TABLE V. DETERMINATION OF BROMIDES IN PRESENCE OF IODIDE KBr Sohtion Taken Ml. 2.0 2.0 2.0 2.0 2.0
NaaSi01
KI Added Gram
Required, Iz = 2Br
0.0150
15.20 15.20 15.20 15.20 15.20
0.0300 0.0450 0.0600 0.0750
M1.
Strength of Na2SzOsused, 1 ml.
KBr in 100 hll. of Found Grams 1.00016 1.00016 1.00016 1.00016 1 00016
= 0.001316
Solution Present Grams 1.0002 1.0002 1.0002 1.0002 1.0002
gram of KBr
PROCEDURE. To the mixture of halides 25 per cent instead of 10 per cent chromic acid was added with nitric acid, thus ensuring complete conversion of iodides to iodate. The rest of the procedure was as described above.
Vol. 14, No. 2
Preliminary experiments were carried out with potassium iodide alone and it was found (Table IV) that no iodine is detected in the carbon tetrachloride extractions. I n Table V are given the results of determination of potassium bromide in the presence of varying concentrations of potassium iodide. The results are self-explanatory. It is evident that the method described can be used safely with great accuracy for the determination of bromides in the presence of iodides and chlorides, provided the chlorides are not present in large amount as in saline waters, “potash salts”, etc.
Literature Cited (1) Baubigny and Rivals, Compt. rend., 124, 859 (1897). (2) Baughman, W. F., and Skinner, W. T., J. IXD.EKG.CHEbf., 11, 954 (1919). (3) Clausmann, Bull. SOC. chem., 9 (4), 188 (1911). (4) Denoel, A., J . pharm. Belg., 22, 179 (1940). (5) Dixon, T. F., Biochem. J., 28, 48 (1934). (6) Edwards, F. W., Nanji, H. R., and Parkes, E. B., Analyst, 61, 743 (1936). (7) Meloche, C. C., and Willard, H. H., J. IND.ESG. CHEM.,14, 422 (1922). (8) Meulen, J. H. van der, Chem. Weekblad, 28, 82 (1931). (9) Sutton, F., “Systematic Handbook of Volumetric Analysis”, London, J. S. A. Churchill, 1935. (10) Swift, E. H., “System of Chemical Analysis”, Now York, Prentioe Hall, 1939. (11) Szabo, Z., 2. anal. Chem., 84, 24 (1931). (12) Weissberger, Proskaner, “Organic Solvents”, Oxford, Clarendon Press, 1935.
An Adjustable Safety Shield ARTHUR FURST, San Francisco Junior College, San Francisco, Calif.
T
HE adjustable safety shield here described was developed b y the writer to overcome the limitations to the arrangement of apparatus when a conventional safety shield is used. The conventional shield consists of either safety glass or wire-encased glass set close to the base legs and rigidly attached to them. protection is afforded at the very bottom where there is no real need, while at the same time the shield protects only a restricted area. The height of the shield is the limiting height of the apparatus. If the arrangement must be modified, the dimensions of the safety shield are a hampering factor. Unless an assortment of shield sizes is kept, only a limited number and types of arrangements can be used.
To give more leeway to the assembling of apparatus and still maintain complete protection, an adjustable, portable safety shield was constructed, using the safety glass from an old automobile wind wing. It was tested by shattering a liter beaker against it from a distance of 4 feet. The glass was enframed in 2 by 4 inch wood, and cushioned by strips of cloth. Into two holes bored in each side were forced the shaft ends of some broken rings. These served to clamp the shield to the ring stands which had been removed from the original iron stands and fastened to large wooden blocks. I
This shield can easily be made higher or lower, and used either vertically or horizontally. Ultimate freedom and flexibility in setting up apparatus are achieved.
