(E) p H > 3.8, Cas> 0.73f. I n this region A E 1 , 2 1 ' 3 p H = -0.03 volt, hEl,z/'Al~g CHAE O > and b E 1 . 3 > ~ =1 Therefore,
ACKNOWLEDGMENT
The authors thank thc Satiollal Council on Science Development for financial support of this project'.
-+ e = U02(OH)2L4-2
U02(0H)2A-
LITERATURE CITED
aiid
(1) Breda, E. J., Meites, L., Reddy, T. B.,
+
2u02(oH)2-l--2 21If
=
+
( uoz)z(o11)2.~2-221f20
!Test, P. W.,Anal. C h i m Acta 14, 300 (1956). ( 2 ) Cannan, It. li., Iiihrirk, .I., J . z4?ti. ChenL. SOC.60, 2314 ( I 938).
(3) Davis, D. G., ANAL CHsnr. 33, 492 (1961). ( 4 ) Feldman, I., Havill, J. IT., J . Am. ; 6 : W.F., Ibzd., 76, 4726 (1954). (6) Harris, W.E., Kolthoff, I. M., Ibid., 69, 446 (1947). ( 7 ) Kolthoff, I. RI., Harris, W.E., Ibid., 68, 1175 (1946). (8) Lai, T. T., Chang, T. L., AXAL.CHERI. 33, 1193 (1961).
(5y$$i:lk, iil?l/,ly&
RECEIVED for review Soveniber 13, 1'362. Accepted March 20, 1063.
Simultaneous Determination of Hypobromite, Bromite, and Bromate Using Ammonium Sulfate M. H. HASHMI and AYYAZ AHMAD AYAZ West Regional laboratories, C.S.I.R.,
Lahore, Pakistan
b The reaction between ammonium sulfate and hypobromite has been developed into a simple and accurate analytical procedure for the simultaneous determination of hypobromite, bromite, and bromate. The influence o f various salts has been discounted. Bromite and bromate added to hypobromite have been determined accurately. Chlorides and bromides, i f present, do not interfere in the determination. Phenol reacts with bromite and hypobromite, and cannot b e used for determination o f the latter in the presence of bromite.
of ammonium sulfate in place of phenol has many advantages as it avoids the phenol-iodine reaction and renders the procedure simple and accurate. Animonium reacts selectively u-ith hypobromite, but not with bromite, and can be used for the estimation of hypobromite in the presence of bromite. The influence of various salts ha$ been eliminated; and hromite arid bromate, added to hypolirornite, h a w been determined accurate!).. C'hloridrk and bromides, if present, do not intcrfere with the determinatiol1,s. EXPERIMENTAL
D
of the kinetics and stability of hypohalites (L), there arose the need of a n analytical procedure for the simultaneous determination of hypobromite, bromite, and bromate ions. Many attempts have been made for the determination of hypobromite in the presence of bromite and bromate ions (1-3). Most of the methods (1, 3 ) are based on the use of phenol for the destruction of hypobromite and involve many complications. The slow action of iodine on phenol leads to 101%-results, and the end point with starch, though sharp, is not permanent (1). The method based on the oxidation of hypobromite to bromate also involves difficulties (6, 7 ) because the bromide present is also oxidized and leads to incorrect results. -4 method has been described ( 5 ) for the estimation of nitrogen uqing hypobromite. In the preqent paper, the same reaction between animoniuin sulfate and liypohroniite has been developed into a siiiiple and accurate analytical procedure for the simultaneous determination of hypobromitc, bromite, and bromate ions. The use
908
URISG THE STUDY
ANALYTICAL CHEMISTRY
Materials. 1111 reagents were analytical grade. Sodium hypobromite was prepared by dissolving 3.5 mi. of bromine in 250 ml. of 10% sodium hydroxide solution a t 0" C. and then making u p to 1 liter. It was stored in a n amber bottle a t room temperature (20" to 35" (3.). Sodium bromite was prepared by the procedure of Chapin ( 1 ) and standardized with arsenious oxide each time ~
Table 1. Recovery o f Added Hypobromite, Bromite, and Bromate from Hypobromite Solution hlillimoles .- __
Comp~nent Added Hypobromite 41 .30
Found
nevi ation
i6.12 3 21
40.9,j 60.25 68.37
76.00 3.24
-0.35 -0.07 +0.15
2.80 2.44 (5.70
2.i6
60.32 68.22
Bromite I3rornate
10.16 13.41 16.70
2.41 6 O!)
10.25 I:< 40
16.78
-0.12
+0.0:3 -0 04 -0.08 -0.01
+00!)
-0.01 $0.08
before use. Secessary correction for ?odium bromate present in sodium bromite solution was always made by potassium iodide-thiosulfate titration. Arsenious oxide (0.12~1: solution) mas prepared by dissolving approximately weighed reagent in 10% sodium hydroxide solution. The solution was made acid to phenolphthalein. Ten grams of solid sodium bicarbonate was added, and the solution was diluted to 1 liter and standardized with iodine. Potassium iodate (0.1~17 solution) n-as prepared from the rcagent previously dried a t 120" C. Procedure. Potassium iodate was used as the primary standard, and the determination was carried out by t h e following methods: (a) To 5 ml. of a niisture containing hypobromite, bromite, and bromate, mas added 3 to 4 grams of solid potassium iodide, followed by 10 ml. of 4 S sulfuric acid. T h e solution was diluted t o twice its volume, and the liberated iodine was titrated with thiosulfate using starch as indicator. 'The titer included h!-pobromite, bromite, and bromate. (b) Five milliliters of mixture was added to a flask containing an excess of ammonium sulfate and about 1 gram of sodium bicarbonate. rlfter 10 minutes, 3 to 4 grams of solid potassium iodide and 10 ml. of 41V sulfuric acid lvas added, and the solut'ion was let stand for 5 minutes before it was diluted to twice its volume and titrated with thiosulfate. The titer included bromite and bromate. (e) To 5 nil. of mixture, a known excess of st,andard arsenious oxide was added. After 5 minutes, 4 to 5 grams of sodium bicarbonate was added fol!owed by dilute acetic acid to neutralize sodium hydroxide until each drop of acetic acid gave free effervrscence. The solution was t i t r a t d with iodine using starch as indicator from IThich the combined normality of hypobromite and bromite was dctermined.
(d) Five milliliters of mixture was added to a flask coni-aining an excess of solid ammonium sulfate and about 1 gram of sodium bicarbonate. After 10 minutei, a known excess of standard arsenious oxide was added and the solution was let stand for 5 minutes before titrating with iodine. The titer corresponded to bromi te. CALCULATIO~%S. For calculations the chmiical rcwtions foi. the above prowdurcs arc as follou 5 :
Table
=
IV.
Effect of Added Salts on Estimation of Hypobromire, Bromite, and Bromatea
Salt added Deviation (ntmole) mmoles Hypobromite Broniite Bromati -0,037 +0.200 +0.030 I O 0 0 CaClZ -0.025 -0.025 f0.025 100.0 hlgClz 200.0 KaCI - 0.125 -0.010 +0.026 Solution ront,aining KaBrO = 43.175 mmoles, NaBrOe = 2.675 mmoles, and NaBrO, I .991 mmoles was analyzed after adding different salts.
For
Stoichiometry OBr21213 IZ BrHzO OBrO414H' 212 Br2H2O OBrOz6161I+ -+ 312 Br~HzO
-
[OBr-] + + + + [OBrO-] + + + + [OBrOz-] + + + + 40Br- + 2SH4+ 4 Br- + Nz + 4HzO [oiir'o-1 OBrO- + N H 4 + + n o reaction: ORrO- + 41- -- 4H+ 212 + Br- + 2H20 [OBrOz-] OBr02- + NH4' no reaction; OBrOr- + 61 + 6H 312 + Br- + 3H20 [ORr-] O R r - + .4s03 - I s O ~ -+~ R r [OBrO-] OBrO- + 2 . 2 ~ 0 , - ~ + Rr... OBr02-2 + no reaction 40Br- + 2SH4+4Br- + ?;z + 4Hz0 OBrO- + NH,+ no reaction; OBrO + ~ A s O S - ~ R r - + 2 . 4 ~ 0 4 - ~[ O B i O -1 OBr02-2 + KH4+ no reaction: OBrOz- + no reaction ... ++
p H 6-9
-4
-+
-
+
-
+
+
addition to hypobromite, also reacts with bromite. The effect of neutral salt addition on the accuracy of the determination was studied. The results in Table IV indicate t h a t the presence of calcium rhloride, magnesium chloride, and sodium chloride do not impair the accuracy of the analysis. DISCUSSION
-+
-
"H 5-9
--t
+
-t
HypnbromitP = titer ( a ) - titer ( b ) = titer ( h ) - [titer ( a ) - titer ((.)I which iu identicd with titer ( d ) Broinite Bromate = titer ( a ) - titer ( c ) Bro mi te = titer (cl)
T h i j method provides a convenient and accurate procedure for the simultaneous determination of hypobromite, bromite, and bromate. The destructioii of hypobromite is carripd out by ammonium sulfate according to the reaction: 2SH,
Table II. Comparison of Total Bromine Contents Distribution of bromine (n')_ _ HypoBro mi t e Bromate Total bromine contents (-v)
bromite 0 .onnn 0.0873 0.0881 0.081 2
*
Differenre
0.0114 0.1139 0.0730 0,1752 0.014!) 0 . 135x 0.021 1 0 .O.i16 0.0841 0.1804 0.0151 Obtained by adding columns 1, 2, and 3. Found by potasviun iodide-thiosulfate titxation. 0 . 0 1 22
Table 111. Reaction of Phenol on Hypobromite and Bromitea
Millimoles Ions unreactecl with Bromateb phenolc Difference -0.007 0 790 0.783 -0.020 1 .I00 1.080 1.160 1.166 +0.006 0.533 0.545 +0.012 0.533 0.533 fO.OOO To the hypobromite solution containing NaBrO = 44.525 mmoles, NaBrOz = 1.860 mmoles, and NaBrOI = 0.625 mmole, different amounts of sodium bromate were added and the solution was analyzed by two different methods. The amount was found by the difference in titer obtained in procedures ( a ) and (c). 0 The amount was found by method (b) except that phenol was used instead of ammonium sulfate and that the results have been expressed in millimoles of bromate for comparison. (I
0.1146 0,1757 0.1548 0.1802
0.0007
0.0005 o.oot0 0.0002
RESULTS
Sodium hypobromite solution was prepared and analyzed for hypobromite, bromite, and bromate contents. T o it, hypobromite, bromite, and bromate were added, and the results in Table I indicate t h a t almost all the added components can be determined accurately. As a further check on the accuracy of the method, the amounts of hypobromite, bromite, and bromate mere determined separately, and the total bromine contents of these components were compared 1% ith those obtained by potassium iodide and thiosulfate titration Results in Table I1 show the reliability of the procedure. Table 111s h o s~a compai i.on betn een the estimation of liroiuate using arsenious oxide and by the phenolpotassium iodide-thiosulfate procedure. The results by both mpthods are comparable and indicate that phenol, in
+ 3SaOBr = 3NaBr + S 2+ 3H20
The reaction is quantitative (8) bctween p H 7 . 5 to 9.5. At this range of hydrogen ion concentration, oxides of nitrogen are not formed; these generally introduce errorb and interfere in the iodometric back titration. To obtain the proper pH, sodium bicarbonate is added in addition to ammonium sulfate. [cf. methods (b) and (d)l. This alivayb fixes the p H at 8 to 9. Ammonium sulfate is superior to phenol because: its use eliminates the slow interference of the latter in tht. iodine titration, thus permitting a sliarli end point n i t h starch, and in contrast to phenol i t reacts only n.ith hypobromite and not n i t h bromite, thu. affording a clear cut determination of the first ion in the presence of the second. (cf. Table 111). LITERATURE CITED
(1) Chapin, R., J . A m . Chem. SOC.56,
2211 (1934). (2) Clsrens: J., Compt. B e n d . 157, 216 11913). '3) Farkas, L LeJvin, M.,ANAL. CHEV. 19. 662 (1927). (4) Hashmi, X ' H . , All, E., Ayaa, A. A , unpublished results (5) Hashmi, ?*I. H , rlli, E., Umar, M. A i x 4 ~ .CHEM 34, (388 (1962). (6) Kolthoff, I. M., Yutzy, H. C., IXD. ENG.CIIEM.,ANAL. ED. 9 , 75 (1937). ( 7 ) hIeulen, J. H., Chem. Weekblad. 28, 82 (1931). (8) Tschepelewetzky, M , Posdniakou a, P., 2. A r ~ a l Chettz. . 84, 106 (1931). RECEIVED for review December 26, 1962 Accepted March 22, 1963. VOL. 35, NO. 7,JUNE 1963
909
