Estimation of Bromide in Presence of Chloride LADISL4US FARKAS
JIEN..ICHEXI LEWIN
Department of Physical C h e m i s t r y , Hebrew University, Jeribsalem
A rapid and convenient method for the determination of bromides in the presence of chlorides and other salts inbolves oxidation of the bromide to hypobromite with a measured amount of hypochlorite at a pH of 9.0 to 9.1, reduction of the hypobromite with alkaline phenol solution, and determination of the remaining hypochlorite with sodium arsenite and iodine solution. The influence of pH, time, and neutral salt content is briefly discussed. Lnder carefully controlled conditions the analytical error does not exceed 0.2'7" of the bromide.
S
ET'ERAL methods for the estimation of bromides in the pres-
ence of chlorides are described in the literature, all based on the oxidation of the bromide ion either to elementary bromine ( 4 ) or t o bromate. The latter method \!-as worked out by van der XTeulen (6) and later modified by Disori (21, Iiolthoff and Yutzy ( b ) ,and others (8). I n this method, a large escess of sodium hypochlorite solution at p H 6 to 7 is used to osidize the bromide t o bromate. After the reduction of the excess hypochlorite, the bromate is est,imated iodonietrically in acid solution. I n the present paper a new analytical procedure is proposed, which is based on the oxidation of the bromide ion t o hypobromite by means of sodium hypochlorite. The hypobromite formed is then estimated in the presence of hypochlorite (3). The determination of microgram quantities of bromides by means of oxidation with hypochlorite has been used by Stenger and Kolthoff ( 7 ) in a semiquantitative method. T h e sodium hypobromite formed at p H 8.7 to 8.8 brominated phenol red t o bromophenol blue, which vas then estimated colorimetrically. Hypochlorite and bromide react according to the equation Br- = BrOC1(1) C10-
+
+
T h e rate of this reaction decreases with increasing p H ( 1 ) and takes for its conipletidn from several minutes ( p H range If to 10) u p t o several hours ( p H range 12 to 14). At lower pH values, a series of other reactions takes place simultaneously, these have not yet been thoroughly investigated, but can be formulated schematically as follows:
+ BrO- = 2C1- + Br03+ 2HC10 2 H + + 2C1- + C103+ 2HC10 = BrOs- + 2H.- + 2C1-
BrO-
(3) (4)
T h e rate of these three reactions increases with decreasing pH. I n van der Meulen's method (6) Reactions 1 to 4 take place, and the bromate formed according to 2 and 4 is mtimated.
Table I. Present Millimole 0.7867 0.7867 0.7867 0.7867 0 . 7867 0.7867 0.7867 0 7867 0 7867 0 7867 0 7867 0 7867 0 3364 0 3364 0 3364 0 7867 0 7867 0 7867 0 7867 0 7867
Influence of pH on Accuracy of Bromide Determination Potassium Bromide Found Ali'd2imoZe 0 7785 0.7805 0 7760 0.7835 0.7822 0 7830 0 7823 0 7875 0 7853 0 7862 0 7854 0.7878 0 3367 3370 0,3364 0,7905 0 7909 0.7977 0.8048 0 8149
.
n.
Error Millimole - 0 0082 - 0 0062 - 0 0107 - 0 0032 - 0.0045 - 0.0037 - 0 0044 +0.0008 4-0 0014 - 0 0005 - 0 0013 - 0 0011 t o . 0003 -0 0006 0 0 + 0 0038 + 0 0042 i0.0110 t o 0181 i o 0282
EXPERIRIESTAL
The solution of potissium bromide used was prepared from analytical-grade potassium bromide and contained 10.150 grams per liter. I t s potassium bromide content was determined gravimetrically as silver bromide. The other solutions used and the experimental procedures employed are described in (3).
Table 11. Influence of Time on .kccuracy of Analysis Time .llin. 10 15 30
( p H 9.2, temperature 18O C.) Potassium Bromide . Present rollrld .llillimole n 2336 0 2333 0 2336 0 2344 0 2336 0 2358 0 2336 0 2380
(2)
2ClO-
CIO-
I n order to wtiniate bromide ioris by oxidation to liypotilo!nite it is essential to carry oat Itoaction 1 a t such a rate and uridt~t.,uch conditions that the side reactions, 2 t o 4, do not take plaw to any appreciable estent. Since the aniount of sodium hypotiromite is calculated from the differencc in the oxidative capacity of collium hypochlorite before and after the osidarion of the brcimide ions, it is evident t h a t if some of the hypochlorite is consumed in Reactions 3 and 4, errors \vi11 occur in the analytical resulti. I t was therefore important to determine the most suitabli. pI€ fur the oxidation of the bromide.
PH 9.9 9.9 9.9 9 65 9.65 9.65 9.65 9.4 9 4 9 0 9.0 9 0 9 0 9 0 9.0 8 8 8.8 8.5 8.5 8 2
For the analysis, a measured aliquot portion of the potassium bromide solution was pipetted into an excess of 0.1 -I' sodium hypochlorite solution, and an appropriate aniount of buffer, usually boric acid, n-as added, folloxed 5 minutes later by phenol and alkali. The estimation was continued as for. the dt>ti:rniination of sodium hypobromite (3j. R E S U L T S A N D DISCUSSION
Table I shows the results obtained in a series of espeririients carried out at various pH values. It can be seen that in the pH range 9.0 to 9.4, results correspond to the theoretical valiiesLe., the error is below 0.2$,--n-hereas outside this pII range the error of analysis is 0.5 to 1%. I n the pH range (3.0 to 9.4, the accuracy of the method is about the same as that of van der Meulen's method. T h e influence of the time of intrxraction of the oxidarion a t pH 9.2 is shown in Table 11, increasing the time of osidation, the results obtained are too high. This is due to the side rt:actions 2, 3, and 4 which occur a t a slon. rate even at pH 9.2. T h e influence of the addition of neutral mlts is summarized in Table 111. The addition of sodium chloride up to a molar ratio S_KBr a_C _ l - 50 does not affect the accuracy of the dcterniinations. I t follow that the hypochlorite may contain considerable amounts of chloride and chlorate ions and does not need to be freshly pre\IeC1.: = 10 pared. T h e alkaline earth salts u p t o a molar ratio 3~
V O L U M E 19, NO. 9
666 111. Influence of Neutral Salts Anal>-& I'res?iJt
I'i,;zs;ium Bromide Found Error
011
'
Salts .\dded
.lli!~i'mole 0 0 0 0 t!
7860 is65 (8i5 is70 i850
Accuracy of
Grams
ACKNOWLEDG>lEST
0007 0002 0008 0003 -0 0 0 i i -0 -0 0 0
0 3345 0 Ti60
-0 0019
0 i784 0 3370
-0 0133 0 0006
0 3346
-0 0018
0 3263
-0 0101
The authors are grateful to R. Bloch, of Palestine Potash, Ltd., Jerusalem, for useful discussions in the course of this investigation. One of the authors (31.I,.) is indebted to Palestine Potash, Ltd., Jerusalem, The Lodzia Textile Co., Ltd., Tel-hviv, and Ata Textile Co., Ltd., Haifa, for a grant which enabled him to carrv out this investigation.
-0 O l O i
Table TV. Determination of Various Amounts of Bromides IiBr Solutwn 10.00 10 00
5.UP 5.02 4 (!4 4 04 2 00 2.00
(pH 9 0 0 , temperature lSJ C.) 0 1 .v Potassium Bromide SaClO Ysed Present Found
30 30 15 15 15 1.5 15
15
K h e n the sample solution contains less than 0.04 gram of bromide a n accurate analysis may still be carried out by using 0.04 A- hypochlorite, 0.04 S arsenite, and 0.02 .V iodine solutions. The amount of phenol added should be proportionally smaller, whereas the other conditions remain unchanged.
101.50 101.50 50.95 50.95 41.00 41 00 20.30 20 30
101.51 101,5l 50.94 50.92 41 05 41.03 20 32 20.29
Error
+o 01 +o 01 -0 01 -0 03
+ O 05
+o
+o
03 02
-0 01
do not interfere n-ith the analysis. .It, higher ratios considerable errors axe encountered, because the hypobromite is not completely destroyed by phenol and alkali. The disturbing effect of the alkaline earth hydrosides is due to the fact that they tend to absorb hl-pobroiiiite. Lvhich is subsequently not attacked by phenol. This dificulty could possibly be overcome by conversion of tlie calciuni and magnesium ions into soluble compleses-e.g., of hesanietaphojpliates. Experiments in this direction are to be carried out, and it is hoped t h a t the method will also prove suitable of bromine brines, xhich usually contain a high lciuni and magnesium salts. Table IV s h o m the results of a series of analyses of various amounts of potassium bromide, carried out a t p H 9.0. About twice tlie theoretical quantity of sodium hypochlorite \vas used. (In general, an excess of 15 t o 20%,is sufficient.) On the basis of these results, the follorving procedure for tlie determination of bromide ions in the presence of chloride ions is recommended. REAGENTS
Reanent; reouired are those used in the work described in the previous paper (3I . The, Iwtnr ot the 0.1 S sodium hvuochlorite solution should - ~~. be dete:inin~tl on the day the bromide analyses are cari,ied out. The reagents nntl the samples for analysis should not contaiii reducing agent3 or ammonium salts. PROCEDURE
to 0.08 gram of potassium bromide. n Erlenmeyer flask of 300-mI. capacity, 15 nil. of hypochlorite are added. The mixture is buffered 1 of 1.7 t o 2.0 nil. of a 5 7 boric acid solution, thus !tal volume to 25 nil. After 5 minutes, 6 ml. of 8 ml. of 0 . 5 7 phenol solution are rapwith vigorous shaking. If the initial aiger than 8 to 10 ml., more alkali should lit, added i n order to bring the final alkalinity to a t least 0.25 S. Slinking is continued for 7 to 10 seconds and then 25 nil. of 0.1 S sodium arsenite are added from a 50-ml. beaker. The 50-nil. benker is rinsed tlvice n-ith distilled water, and then, 5 minutes later, rinsed again with 75 ml. of 5% sodium hicarbonate solution. .icetic acid, 3 S is then added dropwise with vigorous shaking until carbon dioside begins to be evolved. The tit,ration is performed with 0.05 -V iodine solution in the presence of starch, until a permanent light blue color appears. The temperature during titration with iodine should not be over 20' C.
LITERATURE CITED
Bloch, R., Farkas, L., and Lewin, AI., unpublished results. Dixon, T. F., Biochem. J . , 28, 4 8 ( 1 9 3 4 ) . Farkas, L., and Lewin, M . , ASAL. CHEM.,19, 602 ( 1 9 4 7 ) . Kapur, P. L., Verma, M.It., and Khosla, B. D., Ibid., 14, 157 (1942).
Kolthoff, I. XI., and Yutsy, H. C., ICid., 9, 75 ( 1 9 3 7 ) . Meulen, J. H . van der, C'hem. Weelzblad, 28, 82 ( 1 9 3 1 ) . Steiiger, V. .I.,and Kolthoff, I . M.,J . A m . Chem. Soc., 57, 831 (1935).
Willard, H. H., and Heyn, A . H. -I.,ISD.ESG. CHEM.,AXAL. E D , ,15, 321 ( 1 9 4 3 ) . PARTof a thesis submitted by Xlennchem Lewin to the Senate of the Hebrew University, Jerusalem, Palestine, fur the Ph.D. degree.
Hydrogen Discharge Tube GEORGE B. ,IRNOLD
ASD
LEON DONN
Beacon Research Laboratory, The Texas Company, Beacon, S. Y
T
HE high-precision Abbe-type refractometers, recently introduced, 'E, provided with suitable source of illumination for the C (6563 A.) and F (4861 A) lines of the hydrogen spectra, m:ilie possible conventional dispersion measurements of much greater accuracy than those obtained by the method of compensator readings. Many types of hydrogen discharge tubes have heen proposed for the production of the hydrogen spectra (1, S-b) and the description of yet another type would be of little value unless that type of tube offered particular advantages. The tube described in this paper may be operated continuously for several hours \Tit11 little or no attention, provides a light of sufficient intensity for convenient use with an Abbe-type refractometer, requires n relatively low current source, and is easily constructed. I t has been used successfully for several years as fhe source of illumination viith Abbe-type refractometers for making refractive index and dispersion measurements involving the C and F lines of the hydrogen spectra.
:
- E
Figure l.
Hydrogen Discharge Tube
