THE RATES O P T H E REACTIONS I N SOLUTIONS CONTAINING POTASSIUM BROMATE, POTASSIUM IODIDE AND HYDROCHLORIC ACID BY ROBERT H. CLARK
Among the earliest contributions to the literature of this subject is a paper by \V. Ostwald,' who studied the reaction between hydrogen iodide and bromate in order to determine the accelerating influence of different acids. The author did not. attempt to formulate a satisfactory kinetic equation, but calculated the velocity constant from the bi-molecular formula, and came to the conclusion that, in general, the accelerating influence of the different acids is proportional to their affinity constants,2 the chief exception being in the case of chromic acid. I have carried out a number of experiments on the action of chromic acid, which will appear in a second communication. In the same year W. Meyerhoffer3 and 0. B ~ r c h a r d , ~ working independently of each other, investigated the reaction, and both came to the conclusion that the rate could not be represented by the formula of the second order or by any other simple formula. Meyerhoffer ascribed the complications to the influence of the iodine formed by the reaction and proposed the equation
dX
27 =
c
(U-Z)'
X
, but it was shown
later by Meyer' that this equation is not in agreement with the experiments. In 1890 Gaetano Magnanini' made a great many measurements on the rate of this reaction; he, like Ostwald, studied the influence of different acids and noted that the acceleration caused by hydrochloric, nitric and sulphuric acids is not Zeit phys. Cheni., 2, 1 2 7 (1888). See however, Zeit. phys. Chem., 19, 599 ( 1 8 9 1 ) and Table I V of the present paper, p. 684. Ibid., 2, 585 (1888). Ibid., 2, 796 ( 1888). Zeit. phys. Chem., 2, 830 (1888). G a m chim. Ita]., 20, 377 (1890)
680
Rohevt H. CZavk
proportional to their concentrations, but failed to draw any general conclusions. The next paper on the subject, A. A. Noyes” “Contribution to the Knowledge of the Order of Polymolecular Reactions’” contains four series of experiments by W. 0. Scott, in which the initial concentrations of potassium bromate and iodide were varied, while in all the acid was present in constant excess. Comparison of the constants of the second and third order in the different series led to the conclusion that “ the reaction between hydriodic and bromic acids is of the second order.” In the following year in a paper ‘‘ On the Catalytic Effect of Hydrion on Polymolecular Reactions ”’ Noyes showed from certain of Magnanini’s measurements, that the rate of the reaction between hydrobromic and bromic acids is proportional to the square of the concentration of the hydrion. In spite of this large amount of work, however, the author of the most recent text-book on chemical kinetics3 is of the opinion that “ t h e course of the oxidation of hydriodic acid by the oxyacids of the halogens appears to be so intricate that a satisfactory application of the mass law has not yet been made.” The measurements of the present paper show definitely the influence of the concentration of each reagent on the rate, and the extent to which the results are affected by the presence of the products of oxidation, viz., iodine and bromide. Plan of the Experiments In these measurements, in order to trace the effect of the concentrations of each one of the chemicals separately, I have adopted a plan described by Mr. 117. C.‘ Bray4 under the title ‘‘ Method of Constant Rates ” which consists in choosing the concentrations so that “while the amount of change accomplished in a suitable interval of time is sufficient for the Zeit. phys. Chem., 18, I 18(1890). Ibid., 19, 599 (1891). J. TV. Mellor : Chemical Statics and Dynamics,” p. Jour. Phys. Chetn., 7, 93 (1903). (‘
103
(1904).
Reactioizs of Potassizrm Bromate, Iodide,Etc.
68I
requirements of an accurate analysis, yet the fractional alteration in the concentrations of the reagents involved is so small that the rate may be treated as practically constant during the interval. ” Where the reaction has proceeded so far that this assumption could not be made, a correction has been applied for the small changes in concentrations of the reagents involved. In all cases these corrections are comparatively small, the conclusions to be drawn from the experiments being, in general, obvious enough, even without the correction. Method of Working Te?nfierature.-All the measurements were made a t 30°, this temperature being maintained by a thermostat within one-tenth of a degree. Calibration.-All the pipettes used were calibrated by weighing the distilled water discharged, thirty seconds being allowed for drainage. The burettes were calibrated as described in ‘‘ Ostwald’s Hand- und Hilfsbuch,” p. 103. Details o j an Ex+eriment.--Each measurement contained in the following tables involved the preparation of a new reacting mixture. Portions of the stock solutions used in the measurements were kept in the thermostat in glass-stoppered flasks. The potassium bromate was added to a suitable volume of water in a wide-mouthed half-liter glass-stoppered bottle, while the potassium iodide and hydrochloric acid were pipetted into a large test-tube together with enough water to make up a volume of 80 cc. After pipetting out the solutions they were allowed to stand in the thermostat for five minutes, and then the contents of the test-tube were quickly poured into the bottle and shaken, the exact time of mixing being noted. The total volume of the reacting mixture was always 2 5 0 cc. When it was desired to stop the reaction the contents of the bottle were rapidly stirred, I O cc of a halfsaturated ammonium bicarbonate solution were thrown in, and the time was noted. The iodine liberated was then determined with hundredth-normal arsenite.
R o b e d H. Clavk
682
Stock Solutions Potassium Bromate.-o.ozo6 F. made from Merck’s potassium bromate and standardized by decomposing a known volume with excess of potassium iodide and hydrochloric acid, adding excess of the solution of ammonium bicarbonate, and titrating against the volumetric sodium arsenite. Potassium lodide.-0.9890 F. neutralized (to litmus) by hydriodic acid and standardized gravimetrically with silver. Potassium Bromide.--2.002 F. neutralized and standardized with silver. Hydrochloric Acid.-Two solutions 0.9539 F. and 0.9542 F. respectively, by comparison (phenolphthalelin) with a freshly prepared volumetric potash solution, which in turn was standardized with potassium bichromate. Sodium Arsenite.-o.d2504 F. As,O, (0.10017 normal) prepared according to Mohr’ and standardized with dry freshly sublimed iodine. Iodine.-Approximately decinormal, prepared from freshly sublimed iodine and compared frequently with the sodium arsenite, the accurate titre so found being used in the calculations. Ammonium Bicarbonate.-A half-saturated solution was kept under carbon dioxide; if was tested from time to time, and not used unless a distinct blue color was obtained by adding one drop of centinormal iodine to a mixture of 250 cc water, I O cc ammonium bicarbonate, I O cc potassium iodide and 3 cc starch. The Starch was prepared fresh daily: I gram to the liter. All these solutions were diluted to one-tenth their concentration to form the stock solutions ” and volumetric solutions referred to in the preceding section. Explanation of the Tables The numbers at the head of each table, divided by IOO,OOO, give the gram-formula weights of each reagent initially present I‘
Formula weights per liter. Titrirmethode, 9th ed., p. 392.
* Chemisch-Anal.
Reactiom of Potassium Byomate, Iodide, Etc.
t
x
~ , x r o 4 ~ K x ~ o l j
I1
_______ ~ -
5 I0 20
0.46 0.90 1.80
,
2.75
30 45 60
4.00
90
7.60
5.24
I I
0.464 0.907 1.87 2.90 4.32 5 79 8.77
1
928 907 935 966 960 965 973
~
1 ~
99 97 IO0
I
103 104 103
I
104
683
TABLE 111 KBrO,, 20.5;
t
KI, 197.3;
I
x
HC1, 95.15 I
~ K , ~ ~ o ~ , K j < r o ~ ~
x/
______
IO 20
30 45 60 90
0.90 1.80 I 2.75 1 3.99
0.915 1.86 2.88
I I
915 98 930 1 99 1 960 1 102 , 4.30 955 102 5.22 5.73 I 955 I 1 0 2 7.53 I 8.66 1 962 102 Average value, R, = 936 X IO-^
1 ,
TABLE IV K I , 98.67;
KBrO,, 20.5; t ___
1
-- 1
1
x
I
x/
,R,X
HC1, 190.3
Io&iK X
1013
l-___l___
I
IO
1
30 I 5.39 5.91 1970 105 45 7.75 8-87 I970 1 I05 60 I 9.76 111.60 1930 102 90 13-93 j 18.01 2000 I 106 Average value, R, = 1930 X IO-^ ~
i
~
Effect of Chiorion and of Atmospheric Oxygen on the Rate I n order to assure myself that the effect of the hydrochloric acid was due entirely to the concentration of the hydrion I made some measurements in which the concentration of the chlorion was doubled by adding sodium chloride. The rate was the same as in the absence of the salt. The addition of very large quantities of potassium chloride, however, retards the oxidation, see Tables IX and X and p. 688. To find whether the results were affected by access of air,1 I made some preliminary measurements in duplicate, one of each pair under ordinary conditions, and the other in an atmosphere of carefully purified carbon dioxidee2 I Compare Zeit. phys. Chern., 2 , 103 (1888), and Gazz. chim. Ital., 382 (1890). See Dushman : Jour. Phj s. Cheni., 8 (1904).
20,
Reactiom of Potassium Bromate, Iodide, Etc.
68.5
failed to detect any difference in the rates in the two cases, and the subsequent measurements were carried out in air. Effeot of the Concentrations of Bromate, Iodide and Acid on the Rate By comparing Table I with 11, I11 and IV respectively it is readily seen that the velocity of the reaction is proportional to the first power of the concentrations of the bromate and iodide and t o the second power of that of the acid, as represented by the equation: I d~ -_ V ' dt
-
(X--x) V
(B--x) __ . (C--X)~ V - VL
(1)
This conclusion is confirmed by the constancy of K in the tables as calculated from the integrated form of the above equation :-
2 1
)'
x3
(2)
In the tables I have used the symbol x' for the quotient KABCZt/V3,because it gives the amount of iodine that would be liberated in t minutes if the solution retained its original composition throughout the experiment. The amount of iodine actually liberated, x, is naturally less than d,because of the decrease in concentration of the reagents as the reaction proceeds. In calculating K the values of A, B and C denoting respectively the initial quantities of KBrO,, K I and EX 1 have been expressed in the same units as x (see p. 683) ; thus A = 6KBrO,, B = 2/3KI, C = HC1, according to the equation : KBrO, 9KI 6HC1=3KI3$ KBr 6KCl+ 3H,O. For instance in the experiments of Table I, A=123, B =65.78, C =95.1 j. In each table the constant increases slightly as the reaction proceeds ; no importance can be attached to this fact, however, as a change of from O . O j to 0.1cc of the hundredthnormal arsenite used in the analysis would account for the increase.
+
+
+
686
Robert H. CZark
Effect of Bromide Judson and Walker1 have shown that potassium bromide, which is one of the products of the reaction between bromic acid and hydriodic acid, is itself oxidized by bromic acid; this reaction, however, takes place much more slowly than the oxidation of potassium iodide even when equivalent quantities are employed, and in the experiments of Tables I to IV the concentration of the bromide never reached 3 percent of that of the iodide. A few experiments in which small quantities of potassium bromide were added to the reacting mixture gave results identical with those in which no such addition had been made, so that it was not necessary to make any correction for the presence of this product of the reaction. In this connection a number of experiments were undertaken to see whether the two reactions, viz.,the oxidation of potassium iodide and that of potassium bromide by bromic acid, take place independently in the solution. In Tables V and VI1 potassium bromide alone was present; in those of VI and VI11 both bromide and iodide, the latter, however, in comparatively small quantity, as under like conditions the iodide is oxidized 58 times as rapidly as the bromide. In the fourth column of Tables VI and VI11 are entered the sums of the values of x' from Tables I and V, and IV and VI1 respectively; that is to say, the combined amounts of iodine which would have been liberated in solutions containing the bromide and iodide separately; in each case these sums are greater than the amount of iodine set free in the mixture, as given in column four of Tables VI and VII. TABLE V KBrO,,
KBr,
20.5;
1
120 30 45 60 go Jour. Chern. Soc., 73,
'
I
,
1
411
HC1, 95.15
2000; X
I
0.61
I
0.62
'
0.95
0.94 1.42
1.85 2.75 (1898).
~
1.44
1.89 2.86
Reactions of Potassium Bromate, Iodide, Etc.
687
TABLEVI KBrO,, 20.5;
KBr, 2000;
t
X
20
1.28 1.87 2.75 3-40 5.31
30 45 60 90
KI, 98.67; XI
(mixture)
XI
(Sum I and V )
1.31 1-93 2.87 3.58 5.80
I .52
2.39 3.67 4.84 7.82
[Note : As the concentrations of the reagents have the same effect on the rate of oxidation of bromide1 as on that of iodide, the
values of x’ in Tables V and VI1 were calculated from equation (2).
In calculating x’ (mixture) for Tables VI and VI11 the concentration of the bromide has been regarded as constant, and x’ has been computed by means of a modified form of equation ( 2 ) , viz. : ( I / 2A
x’=x+
+I /C) +(X-y) X’
’/ 2B
(2 bis)
where y is the value of x in Table V, and x -y is substituted for x in the term x2/2B, y being regarded as the iodine liberated (in experiments VI) by the bromine set free by the action of bromate on bromide, and x-y that liberated by direct action of bromate on iodide.]
TABLE VI1 KBrO,, 20.5; t
30 2o 45
60
HCl, 190.3
KBr, 2000; i
I I
1
I
x
;:;: 1!
5.39 7.00 9.71
Judson and Walker : loc. cit.
1
I
XI
2.46 3-91 5-70 7.50 10.71
~
Robert H. Clark
688
TABLE VI11 KBrO,,
20
KBr,
5;
t i 20
1
30
I
45 60
I
HC1, 190.3
KI, 98.67; ~~
4.75 7.35 10.60 13.40 18.58
I
5.01 7.98
1
12.02
1
15.73 23.43
~~
(Sum I V and V I I ) ~-
x / (mixture)
X
’
90
2000;
XI
6.20 9.82 ‘4.57 19.10 28.72
I
i 1
The difference between “d mixture”. and ‘‘3’sum” in Tables VI and VI11 was found to be due to the presence of the large quantities of potassium salts, which, as the readings of Tables I X and X show, retard the oxidation of potassium iodide. The solutions used in the experiments of these two Tables (IX and X) are the same as those of Tables I and IV, with the addition of enough potassium chloride to make the concentration of the potassium ion the same as in the experiments of Tables V and VII. As is shown in the last columns of Tables IX and X, the iodine liberated in solutions containing both iodide and bromide is the sum of that liberated in solutions containing iodide alone, jdzds the iodine equivalent of the bromide liberated in the absence of iodide. Thus, the two reactions-oxidation of iodide by bromic acid, and oxidation of bromide by bromic acid-proceed independently in the same solution. TABLE IX KBrO,, 20.5 ; KC1, 2000; KI, 98.67 ; HC1, 95.15 ~ _ _ ~ _ _
t 20
I
x
~
I
I
30
0.67 1.01
’
x/
0.68
1 x’ (Sum
I
1.03 I
60 90
1.93 I
2.91
3.10
v and 1x1 1
1.30 I .97 2.96 3.78 5.85
~
I
I
__
x~ mixture ( V I )
1.31 I .93 2.87 3.58 5.80
Renctioizs of Potassz'uvz Byomate, lodide, Etc.
689
TABLE X KBrO,, 20.5; t
1
x
KCI,
i
K I , 98.67;
2000;
XI
1
XI
(Sum V I I a n d X )
5.22 8.19
HC1, 190.3
1 I
'
from VI11
5.01 7.98 12.02
12.18
15.81 23.77
XI
~
1
15-73 23.43
This simple relation makes it very easy to allow for the effect of the bromide which is formed from the bromate by the action of hydriodic acid. Judson and Walker have shown that the form of the equation for the rate of oxidation of bromide by bromate is the same as that of my equation I ; and the value of its constant calculated from the experiments of Table V, corrected for the high concentration of the potassium ion, and expressed in my units, is 2 . 2 X 1 0 - 1 3 . The bromine formed by the oxidation of the bromide would, of course, react instantaneously with the potassium iodide, and liberate an equivalent amount of iodine, so that the total amount of iodine liberated in the time t is governed by the following differential equation, in which D represents the number of equivalents of bromide initially present.
In all the experiments of this paper, except those in which potassium bromide was added at the beginning, D =o, and the last term of equation ( 3 ) may be neglected. Effeet of Iodine The only other product of the reaction which might influence the rate is iodine. In order to study its effect I undertook the experiments of Table X I in which iodine was dissolved in the stock solution of potassium iodide and its amount determined by titration. The first column of the table gives the amount of free iodine initially present in the reacting mixture expressed in
cubic centimeters of 0.01001 7 normal arsenite; the second, under “ K I Corr.,” the potassium iodide initially present, which was calculated by subtracting one-half the number in the first column from 98.67 (which was the amount of potassium iodide in the solution before addition of iodine), according t o the equation: KI + I, = KI,. Under x is entered the amount of iodine liberated during the time t (minutes), obtained by subtracting the initial iodine from the “titration.” Under “ x calc” is given the amount of iodine that would be liberated in the same time in solutions which contained throughout the experiment the amount of bromate and acid entered a t the head of the table, and the amount of potassium iodide entered in the second column under “ KI corr.,” but no “ initial iodine.” It will be noted that the difference between “x” and “ x calc.” entered in the last column of Table XI, although small, are all positive, and increase with increase in the amount of iodine present. This is in accord with the results of Mr. Dushman’s measurements on the rate of oxidation of potassium iodide by iodic acid in the presence of free iodine, and points to the oxidation of triiodion by bromic acid. The correction for this subsidiary reaction is so small, however, that the relations between concentrations and rate given by equation 2 should hold whether free iodine be present or not, and the equation should be able to account for the whole progress of the reaction between bromic and hydriodic acids from its commencement to its end. This conclusion is borne out by the experiments recorded in Table XLI of the Appendix, for which I am indebted to Mr. F. C. Bowman, where the value of K remains constant within I or 2 percent while 95 percent of the bromate is reduced. Temperature CoeBoient To find the temperature cqefficient, I made a series of measurements’at 30°, 25’ and oo C.
Reactions of Potassium &ornate, Iodide,Etc.
691
TABLE XI KBrO,, 20.5; Initial I _____
1
K I corr.
~
HCl, 190
K I , 98.67; t
I Titration
P
x calc.
Diff.
9.60 13.40 16.75
9.52 13.31 I 6.66
0.08 0.09 0.09
9.33
9.15
0.18
X
I
--I
60 90
~
94.80
I20
92.80
60
92.80
90
92.80
I20
90.28
60
9.60 13.40 16.75 17.07 I 7.06 20.68 20.75 23.88 23.90 20.75 20.78 24.70 24.58 27.78 27.78 25.77
-
8.99
8.74
0.24
16.78
90.28
90
29.59
12.81
12.32
0.49
16.78
90.28
I20
15.70
15.38
0.32
20.92
88.2 I
60
8.93
8.60
0.33
20.92
88.21
90
20.92
88.2 I
I20
40.54
78.40
60
40.54
78.40
90
40.54 5 2.40
78.40
I20
72.47
60
52.40
72.47
90
52.40
72.47
I20
0 0 0
7*73 7.73 7.73 11.75
1
~
I 1
,
98.67 98.67 98.67
I20
60 94a80 94.80
90
I
11.75 11.75
~
I
16.78
~
I
32.43 32.50 29.88 29.82 33.51 33.46 36.60 36.42 48.26 I
51.46 51.43 54-70 54.58 60.05
I:;:
{ 65.98 65.86
12.98
12.80
0.18
16.16
15.99
0.17
9.01
8.94
0.07
12.89
12.56
0-33
16.03
15-75
0.28
12.56
12.07
0.49
15.59
15.16
0.43
7.72
7.60
0.12
10.91
10.74
0.17
14. IO
13.51
7 -65 10.62
10.02
0.59 0.52 0.60
13.52
12.66
0.86
7.13
692
RoOevt H. CZavk
1.840.65 1.85 0.88 I . 89 1.30 1.87 1.75 1.89 2.58 1.97 3.38
0.661 33 0 . 8 9 , 30 1.33 1 29 I 80 30 2 . 7 0 1 30 3 58 1 30
I7 16 1.84 16 I .87 16 I .85 16 1.85 16
The average value of the “temperature coefficient” of the rate. or the factor by which the rate is multiplied for a rise of IO’ in the temperature, may be found by taking the cube roct of the ratio between the rates a t 30’ and oo C. ; it is I .8j . The coefficients determined from the measurements a t 30’ and 2 j 0 C. (which are entered in the table “ a t 2 5 ’ ” ) are practically the same, or if anything, a little higher, see Table X I I I . Appendix Magnanini’s experiments, carried out in 1890,’ some of those of Ostwald’s2 and the experiments of Noyes‘ are here recalculated. A t the head of each table I have given the initial composition of the reacting mixture, the numbers divided by IOO,OOO denoting gram-formula weights of the reagent initially present, the volume being I O cc in all of Magnanini’s and Ostwald’s measurements, while in Noyes’ the numbers recorded are for a volume of I litre. In all these experiments the temperature was 25OC. Mr. I?. C. Bowman’s experiments were carried out in this laboratory a t oo C., and the numbers recorded from his experiments are for a volume of I litre. Gazz. chim. Ital., 2 0 , 377 (1890). Zeit. phys. Chem., 2, 127 (1888). Ibid., 18, r r 8 (1890).
1.87
Reactions of Potassimn Bromate, Iodide, Etc.
69 3
In the first columr, of the tables (under t ) is entered the duration of the experiments in minutes; in the second, the amoimt of iodine liberated .x (in cubic centimeters of . ~ / I O O thiosulphate) ; where Magnanini gave the result of duplicate experiments, I have taken the average. In the third and last column I have entered the value of the constant K of the equation :
where A , B and C are taken from the heads of the table, and V is the volume in litres, e. g., for Table XV, A = I I. I I , B = 7.41, C =24.07, V -0.01. See page 685. In computing the values of K , I made use of “ The Method of Areas,” described by Mr. R. E. De Lury.’ In order to facilitate comparison of the values of K so obtained, I have brought them together in the last table. The constants bracketed have been calculated from the experimental data by making use of the temperature coefficient 1.85 obtained from Table XIII. In the experiments where excess of hydrochloric or nitric acid was used, Magnanini’s values agree m-ith niy own for the same temperature; replacing these monobasic acids by sulphuric acid, takes about 33 percent of K, corresponding to a difference of 1 2 percent in the dissociation, which is a fair agreement with the results of measurements of the electrical conductivity. In the experiments in which the concentration of the hydrion was large, the constants are uniform ; where however their concentration is small, the constant shows a falling off. This is in line with the results of Mr. T. C. Bray’s experiments on the oxidation of hydrogen iodide by chloric acid. The values of the constants derived from Ostwald’s measurements are somewhat smaller than those from the corresponding measurements of Magnanini. Addition of chloric acid and of hydrobromic acid increases the constant Jour. Phys. Chem., gz (1903).
* Ibid., 7,
IO, 425
1906.
Robert H.CZark
694
very slightly, due no doubt to the oxidation of the bromion or to the reduction of the chlorate. Noyes and Scott worked with the potassium salts of bromic acid and hydriodic acid in presence of a constant amount of hydrochloric acid ; their constant agrees very closely with my own. Magnanini’s Measwevieni!s
TABLE XV
TABLE XIV HI,II.II
HBrO,, 1.85;
HBrO,, 1.85; H I ,
11.11;
HCI, KX
t 0.82
1
1.44 1 1.46 1 1.84 I 2.05
2.72 2.96 3.69 3-80 4.82
’ 1
~
I
142 119 116
3 9
100
1.5
99 93 91
I7 28 31 35 40
0.82 I .05
2
88 89
86
11.11 1 0 ~ ~
99
87 84 85 81 84 83 84 86
2.35 3.27 3.38 4.38 4.50 4.68 5.10
I
TABLE XVI HBrO,, 1.85; HI, 1 1 . 1 1 ; HCI, 2 2 . 2 2 1
K X IO'^
X
85 83
1-43 2.98 4. I9 4.93 5.06 5.28
2
6 I2
I7 I8 20
80
80 80 81
I. 1
f 2
4 6 7 8
X
2.55 3.94 4-72 5.15 5.33
~
8 IO
I1
2.03 3.17 3 93 4.52 4.90 5.08
83 82 81
81 80 79
TABLE XIX HBrO,, 1.E ; H I , I I , I I ; H N O , , ~ ~ . ~ ~
TABLE XVIII HBrO,,
2
4 6
KX
1 0 ~ ~
t
I X
68
2
70 70 72
6
2.88
I2
72
19
4. I9 4.84 5.14
I7
1.37
KX
IO’,
82 78 77 77 78
Reactions of Potassium Bromate, Iodide, Etc.
695
TABLE XX TABLE XXI HBrO,, 1.85; HI, 11.11; HNO,, 33.33 HBrO,, 1.85;HI, I 1 . 1 1 ; H?;0,,44.44
t
l
2
4 6 8
I
IO 11
1
x
1
K X rol’
-~
2.03 3.06 3.83 4.4’ 4.89 5.03
t
77 73 72
I--
2
72 ~
l
-
4
1
6 8
i
K
x
X
10”
68
2.5: 3.80 4.60 5.19
67 66 67
72
72
TABLE XXIII TABLE XXII HBrO,, I .85; H I , I I . I I ; H,SO,, HBrO,, 1.85;HI, 11.11; H,SO,, 5 . 5 5 -
t
i
x
9 I7 31 46
I
KX
IO]’
81 71 69 69 67 66 68
2.10
3.07 4.20 4.8 I
11.11;
HC1,
20
25
28
3’
’ K X xolR
2
4.32 5.09
39
I
X I
2
9
t _-___I
---I
39
6 9
’ 1
12
1
I5
1
21
I
23
24
27
K
1
1.23 2.55 3.25 3.78 4.23 488
52
52 52 52
i
i I
1
1
5.02
5.02
5.34
X rol, 57 53
TABLE XXV HBrO,, 5 . 5 5 ; HI,
22.22
I
I
1
I .04 2.99 4.51 4.87 5.11 5.26
2
9
TABLE XXIV HBrO,, 1.85: HI,
x
t
II.II
,
‘11.1r
K
x 1013 106 96 95 94 gj 93 95 92
696
Robevt H. Clay8
TABLE XXVII HBrO,, 1.85; KBrO,, 3.70; H I , 11.11
TABLE XXVI HI,
HBrO,, 9.26;
11.11
-
I
KX
1013
-
2
4 6 8 10
'.
91 90
2.30 3.56 4.36 4.94 5.43
20
0.83 1.85 2.46 2-75 3.41 3.60
28
4.25
2
6 9
89
88 89
I2
I7
46
TABLE XXVIII HBrO,, I .8 j ; KBrO,, 9.25; H I , I 1.1I _
t
I
_
16
107 107
99 99 96 96 95 96
4.86 5.15
41
\
I
~
X
I
6 9 I2
I8 22
25
88
I
3.87
1
4.97 5.16
j
87 87 87 86
,
Ostwald' s Measuremen is TABLE XXIX TABLE XXX HBrO,, 1.856; HI, 11.11 HBrO,, 1.t 6; H I , 11.11; H,SO,, 5.55 K X lola
f I 21
4' 81 146 20I
301 431
0.22
-
1.89 2.81 3.93 4.83 5.37 5.89 6.36
93 92 94 94 96 96 98
t
X
2.04 3.07 4.17 5.27 5.67 6.14 6.39
K X iolY
59 61 63 64 64 65 65
Reactions o f Potassium BYomate, Iodide, Etc.
697
TABLE XXXII HBrO,, I.8j;HI, I I . I I ; H N O , ,11.11 t
x
K X iold
9
2.46 3.54 4.63 5.20 5.60 5.90 6.20
85 81 84 85 86 87 85
'7 3I
41 51
61 7'
I ~
t
84
2.44 3.5 I 4.63 5.18 5.55 5.86 6.09
9
'7 31 41 51
61 71
82 82
84 81 80 80
TABLE XXXIV TABLE XXXIII I . 8 j ; H I , I I . I J ; H C ~ O1 1~. 1,1 HBrO,, HBrO,, '.85;HI, I I . I I ; H C I O 1~1,. 1 1 ___-_____ t
x
I
K
x 1013
t
i
I
KXIO'~
I I
I
90
9
2.54
I7
3.54 4.35 4.77
88
'7
89 88
25
5.56 5.85
89
25 33 4' 51
61
5.18
88 88
9
1 I
33
2.43 3.52
85 82
4.25
4.71 5.15 5.56 5.78
61
1
1 I
84 83 84
85
85
TABLE XXXV TABLE XXXVI HBrO,, 1.85; HI, 1 1 . 1 1 ; H,SO,, 5 . 5 5 HBrO,, 1.85; H I , 1 1 . 1 1 ; HBr, 1 1 . 1 1 t
9
2.40
81
17
3.41 4.16 4.65 5.05 5.40 5.76
80
9 17
81 81 81 81
33 41
81
61
25
33 41 51
61
25
51
l
x
I
2.59 3.68 4.43 4.94 5.34 5.72 6.04
89 90
92 93 94 95 96
Rodert H. Clark Noyes' Measuremen i s
TABLE XXXVII KBrO,, 166; K I ,
1000;
2
I I2
4
192 279 35 8 423 479 j26 562
7 I1
16 22
30 40
63 62 62 62 62 62 62 62
TABLE XXXIX KBrO,, 83; KI,
1*5 3 5 8
1000;
x
t
K I , 500; x
K X IO^$
1.5 3 5 8
46 88 125
65 68 66 70 70 72 73
I80
I2
233 261 294
=7 23
I'tXlO'~
68 68 68 65 63 60 60
48 90 I34 I79 290
t
'
2.5 5.5 9
!
15
23 36 58
' '
x
K I , 4960;
t
x
I12
I55 I94 275
6 19 30 40 50 60 70 80
62.4 155.8 206.6 238.8 26 I 2 7 6.4 290.2 299.6 315.6
100
H,SO,, 1666.6
Percent bromate decomposed
18.8 46.8 62.3 72. I
78.7 83.3 87.6 90.2 95.1
K
HC1, 4000 KX
1013
68 68 72 71 72 74 71
40 79
F. C. Bowmax's Mensuvemeizts TABLE XLI KBrO,, 55.26;
HC1, 4000
1
TABLE XI, Hc1, 4000 KBrO,, 83; K I , 5 0 0 ;
I2
17 23
TABLE XXXVIII
HC1, 4000 KBrO,, 8 3 ;
x 10'4 98 98 99 99 98 97 97 97 98
Reactions o f Potassium B ~ o m a t eIodide, , Etc.
699
Z
0
w
rc
m
*.
..
P,
t 3
a
..
wtd
trl
-2,
"C
& ....-..--
n
5.
e
^I-
2
W
cn
w
H
P W
".: v)
-
0
t
ch
ch Q1
".
$ li 0 CD 3
c w.
2
v
700
Reactions of Potassium Bffomale,Iodide, Etc.
Summary (I) The rate a t which iodine is liberated in solutions containing potassium bromate, potassium iodide and hydrochloric acid is proportional to the concentration of the bromate, the concentration of the iodide, and the square of the concentration of the acid. (2) In solutions containing potassium bromate, iodide, bromide and hydrochloric acid the two haloid salts are oxidized independently. (3) The potassium triiodide formed by the oxidation of iodide adds very slightly to the rate of reduction of bromate; so that, in first approximation, the effect on the rate produced by the iodine liberated during the reaction may be neglected. (4) Thus the progress of the reaction may be expressed by a simple differential equation (see equation I , p. 6 8 5 ) , which is shown to be in accordance with the experiments, A term to represent the effect due to the bromide formed during the reaction may be introduced into the equation (see equation 3 ) . (5) Raising the temperature 10' multiplies the rate by 1.85. (6) The equations developed in this paper have been
used to recalculate Magnanini's, Ostwald's and Noyes' measurements. (See Appendix.) These measurements were carried out in the chemical laboratory of the University of Toronto during the winter of 1904-5; and in conclusion, I wish to express my sincerest thanks to Prof. W. Lash Miller for suggesting this research and for his supervision throughout the work. The Unzverszty
0)
Toronto,
June, 1906
CONTENTS PAGE
Introduction : Plan of the Experiments .................................................. 679 Method of Working : Stock Solutions, Explanation of Tables ................... 681 Effect of Chlorioti and Oxygen on the Rate ............................................. 684 Effect of the Concentrations of Bromate, Iodide and Acid on the Rate Effect of Bromide on the Rate; the Two Reactions are Independent .... Differential Equations.. .................................................................... 685, 689 Effect of Iodine on the Rate ........................................................... 689 Temperature Coefficieiit ........................................................................ 690 Appendix : Recalculation of Measurements by Ost .................. 692 and Bowman ................................................ ...................... ..................700 Summary. ...........................
