T H E SOLUBILITY OF SOLUBLE ELECTROLYTES* 11. The Solubility of the Alkali and Alkaline Earth Bromides in Hydrobromic Acid BY ARTHUR F. SCOTT AND EDWARD J . DURHAM
The material presented in this paper was obtained in order to supplement the already existing data of Engel, Armstrong and Eyre, Masson, and Ingham for the alkali and alkaline earth chlorides in hydrochloric acid. I n a subsequent paper these and other data will be discussed from a theoretical standpoint. Apparatus The Thermostat.-All the measurements were carried out in a specially designed thermostat of seventy-five litem capacity, the essential features of which were as follows. The tank of welded copper was suitably insulated with four inches of shredded asbestos and magnesia packing in the interspace between the tank and its containing box of stout oak. Around the inside of the tank was a coil of three-eighths inch copper tubing through whichicewater was passedfor coolingpurposes. Stirring was accomplished by means of a fourinch, four-bladed propeller driven by a one-sixth horsepower motor connected through a worm and worm gear to give a speed of 800 R.P.M. The shaft for holding the saturation bottles extended horizontally the length of the bath and was driven from the same motor by an external belt connection and bevel gears in the bath a t a speed of 60 R.P.M Heating was accomplished by means of a 25o-watt knife-type heater controlled through a four-fingered regulator of the usual kind and a relay. The regulator was filled with thoroughly dried ethyl acetate which has proven more satisfactory for temperatures up to fifty degrees than the commonly used toluene. The temperature of the bath as determined with a 100' thermometer calibrated by the U. S. Bureau of Standards was 25.00 .oI'. Exploration with a Beckmann thermometer showed that the temperature was constant throughout the bath within the above-mentioned limits a t all times. The Saturation Bottles.-These were z jo cc glass-stoppered pyrex bottles, the necks and stoppers of which were protected from the liquid in the bath by means of glass caps held in place by rubber rings just above the junction of the neck and bottle proper. The glass stoppers were held in place inside the protecting caps by tightly-fitting rubber stoppers. The bottles themselves were secured in alternate and opposite positions and also a t right angles to the shaft by adjustable brass clamps, which also insured the tightness of the protecting caps.
*
* Contribution from the Department of Chemistry of The Rice Institute.
53 2
ARTHUR F. SCOTT A S D EDWARD J. DURHAM
Materials Hydrobromic acid was made by passing thoroughly washed hydrogen sulfide into pure bromine. After separating the sulfur and sulfur bromide by decantation, barium hydroxide was added to precipitate sulfuric acid formed during the reaction; the mixture was heated and the sulfate and additional coagulated sulfur were filtered off. The resulting solution was distilled and the portion coming over between 118" and 1 2 6 " was collected and redistilled as before. The resulting product, a constant-boiling mixture of hydrobromic acid containing about forty-seven percent hydrogen bromide, was stored in pyrex bottles. Bromides. Samples of lithium, magnesium, strontium, barium, and calcium bromides were prepared by dissolving the chemically pure carbonates, which had been washed five or six times by decantation, in a slight excess of pure hydrobromic acid. The solutions were evaporated to dryness to eliminate the excess acid, then redissolved and filtered through a Munroe crucible before crystallization. The crystals were drained from the mother liquor and washed sparingly on a porcelain Buchner funnel. Sodium bromide was prepared in a like manner from recrystallized sodium carbonate and hydrobromic acid. Potassium bromide was obtained by recrystallization of a sample of C. P. salt. I t was found necessary, however, in this process as in previous purifications to filter the dissolved salt through a Munroe crucible in order to eliminate the foreign matter which seems to be present invariably in the best commercial preparations. It was soon discovered on making the first acid addition to this potassium bromide that free bromine was liberated in some quantity. This sample after treatment with an excess of hydrobromic acid and subsequent evaporation and recrystallization was judged to be satisfactory. Ammonium bromide and a sample of calcium bromide were prepared from the C. P. salts in the same manner as was finally adopted for the potassium bromide. Procedure To determine the solubility of the pure salts, solutions were made up in the saturation bottles with distilled water and enough salt t o leave about twenty grams excess. Subsequently the acidities of these solutions were adjusted roughly by the additions of suitable amounts of forty-seven percent hydrobromic acid. The salt was always kept in excess by further additions of solid salt when necessary. I n preparing the most acid solutions of calcium bromide and lithium bromide, it was necessary, because of their high solubilities and relatively slight precipitating effect of the acid to dissolve the salt directly in the hydrobromic acid solution. The solutions were usually adjusted at night, allowed to stand until morning in the thermostat, and then agitated continuously for about nine hours. After stopping the rotation of the bottles the excess salt was allowed t o settle for a t least half an hour and samples were then transferred to tared weighing bottles by means of warmed pipets attached to short filtering tubes
THE SOLUBILITY O F SOLUBLE ELECTROLYTES
533
somewhat similar to those described by Richards.' These filtering tubes were about two inches long with a short bend a t the lower end. The inlet opening was on the top side of this bend so that there would be no tendency for salt to be drawn into the opening on the application of suction. In addition to this precaution a filter plug of cotton or asbestos was always placed in the tube. In order to be certain that the original period of agitation was sufficient to insure complete saturation, samples of a number of the solutions were taken after an additional twelve hours standing followed by seven or eight hours further agitation. The results of these experiments are given in Table I. The samples in the weighing bottles were allowed to reach the temperature of the balance room and were then weighed, usually within an hour of being taken. Analyses were made on aliquot portions of the suitably diluted samples. Acidity was determined by titration with twentieth normal potassium hydroxide solution which was standardized against a hydrochloric acid solution whose strength had been obtained gravimetrically. Total bromine was determined by the Volhard method, using tenth normal silver nitrate and twentieth normal ammonium thiocyanate solutions; the former was checked against a sodium chloride solution standardized gravimetrically and the latter was titrated against the silver solution. The strengths of the solutions were never allowed to become doubtful since they were made up and standardized in two liter portions as needed. Because of the relatively small acid content of some of the samples it was considered advisable, in order to obtain the maximum precision offered by the analytical methods employed] to take one large sample (I 5-2 j gms.) for the acid analysis. To make certain that this sample was representative of the saturated solution it was also analyzed for total bromine and the result compared with the total bromine found in a second separate sample (5-7 gms.). To determine whether the above procedure was justified, solutions of three salts were examined by taking two separate samples and analyzing each for total bromine and acid. In addition the acid content of a third sample was found. The results obtained are given below, and are expressed as grams per I O O grams solution. Further, each value in this and the following table is the mean of duplicate analyses. Salt Sample
A B C
KBr and HRr HBr Total as Br Br
6.89 6.90 6.90
27.70 27.71
-
BaBrl and HBr HBr Total as Br Br 5.26 27.16
5.31 5.30
27.23
-
CaBrp and HBr HBr Total as Br Br
3.44 3.45 3.43
46.77 46.85
-
As a further illustration of the nature of agreement between duplicate samples, the following data showing total bromine content for the sodium bromide series are representative. 'Richards and Fraprie: Am. Chem. J., 26, 75 (1901).
ARTHUR F. SCOTT AND EDWARD J. DURHAM
53 4
Total bromine- gxns. per XaBr solution
IOO
gms. soh.
Sample A
Sample B
37.43 37.59 37.76 38.11 38.63
37.46 37.59 37.86 38.I9 38.65
All the volumetric apparatus employed was carefully calibrated and temperature corrections were applied throughout. The weights were gold plated and had recently been calibrated by a modified Richards method. All sample weights were corrected to vacuum.
Results I n Table I are given data showing the effect of prolonged agitation on the solubility of several of the salts and mixtures of salt and acid. Here also each value represents the mean of duplicate analyses. TABLE I Effect of Length of Agitation on Attainment of Saturation. Salt
KBr & HBr BaBrz &
Time of agitation
Hours 9 18
411 values in gms. per roo gms. soln.
Acid a8 Br 6.90 6.89
9 I7
5.30 526
10
-
Total Br
HBr
Salt
27.71 27.70
6.99 6.98
30.99 30.99
27.23 27.16
5.37 5.33
40.78
__
60.49 60.32
40.72
HBr LiBr
21
SrBrs CaBrz
55.66 55
21
32.22 32.28
8 16.j
46.80 46.80
IO
49.89 49.97
-
58.53 58'53
46.85 8 CaBrn 3.48 54.29 3.44 & 3.48 54.19 46.77 3.44 I9 HBr It is evident from the above data that the nine-hour period of continuous agitation employed in this investigation can be considered sufficient to insure complete saturation.
THE SOLUBILITY O F SOLUBbE ELECTROLYTES
535
I n Table I1 are collected the summarized data for the eight alkali and alkaline earth bromides measured. Each value represents the mean of duplicate analyses on at least two separate samples.
TABLE I1 Solubility per IOO gms. solution. - in gms. Salt
KBr
SaBr
Acid as Rr
6.90 13.06 17.84 -
4.55 8.93 12.82 1 7 .43
NH,Br
__ 12.37
16.73 22.49
LiBr ( 5.37)
(23.63) (29.53)
BaBrz
SrBr,
5.28 9.07 12.65
27.28
HBr __
6.98
27 .;r
'3.23 18.o;
37.45 37 4 9 37.81 38.15 38.64
4.61 9.04 12.98 Tj.6j
48.22 42 .5j 37.19 32.62
__
43.86 27 .91 24.06 15.96
35.79 35.43 36.61 36.40 55.59 (56.24) (58.68) (61.23)
1 2 . j3
16.94 22.72
~
( 5.44)
(23.93) (29.90) __
27.20
27.57 28.IO
5.35 9.19 12.81
-
32.2j
-
3.72 9.27 1; .28
32.90 33.95 3j.60
4.64 9.71 14.61
43.33 44.05 44.72 45.47
__
3.44 7.14 (10.;0)
Salt
40.62 30.99 22.69 17.60
28.6j 29.66
27.04
?tlgBr,
CaBr2
Toial Br
46.80 46.81 47 ' I 9 (49.62)
3.77 9.39 17
.so
4.70
9.83 1 4 . 79
3.48 i.23 (10.84)
27.31
60.41 (55.29) (38.09) (34.45) 50.28 40.76 34.40 28.73 49.93 45.18 38.21 28.36 49.93 45.40 40.33 35.55 58.53 54.24 50.09 (48.67)
536
ARTHUR F. SCOTT AND EDWARD J. DURHAM
Since considerable care was exercised in making the present determinations the init.ial solubilities have additional significance. Therefore, in Table I11 is presented a comparison of the present data with those given in the literature.
TABLE I11 Comparison of Solubility Data at 2 5’. Gms. salt per Salt
KBr
Present values
40.62
Other data
IOO
gms. solution
Observer
40.57 40.4
Scott and Frazierl Average C U ~ V ~ ~
J J ~ J ~
NaBr
48.22
48.61 48.3
Scott and Frazier’ de Coppet3
NHIBr
43.86
43.7 44.2
Eder7 Smith and Eastlake*
LiBr
60.41
64.8
KrernersBa
BaBr3
50.28
jO.0
j I . IO
Etard2 KremersGb Milikang
49.79
Milikang
51.4
SrBrz
49.93
MgBrz
49.93
49.4
Menschut kinlo
CaBr2
58.53
60.j
Kremeda Milikang
60.07
The only mixtures of salt and acid with which our values can be compared are those of Dittell for sodium bromide. Although his measurements were made a t zo”C. and are therefore not directly comparable, they give, when plotted, practically the same curve as the present data. This paper of Ditte was discovered only after the conclusion of the present investigation and, curiously enough, has been overlooked by all the compilers of the standard references on solubility.12 Scott and Frazier: J. Phys. Chem., 31, 459 (1927). Etard: Ann. CLm. Phys., 2, 503 (1894). de Coppet: Ann. Chim. Phys., 30, 4x1 (1883). Tilden and Shenstone: Proc. Roy. Soc., 35, 345 (1883). 6 Meusser: Z. anorg. Chem., 44,79 (1905). sa Krerners: Ann. Physik Chem., 103, 57 (1858). Sb Kremers: Ann. Physik Chem., 99, 25 (1856). Eder: Sitzb. &ad. Wiss. Wien, 82, 1284 (1880). 9 Smith and Eastlake: 3. Am. Chem. Soc., 38, 1261(1916). Milikan: Disa. Leiden, (1914). Io Menschutkin: Z. anorg. Chem., 52, 152 (1907). Ditte: Ann. Chim. Phys. ( i ) ,10, 556 (1897). l2 Including, “International Critiral Tables,” Comey’s “Dictionary of Solubility,” Seidell’a “Solubilities,” Landolt-Bornstein, and Eyre’s Compilation in the Reports of the British Aasocistion.
’
THE SOLUBILITY O F SOLUBLE ELECTROLYTES
53 7
Discussion During the course of the work an interesting phenomenon was noted in connection with several of the saturated solutions. On addition of hydrobromic acid to a calcium bromide solution, a distinct pink color appeared. Moreover, the solution showed a tendency to fume which increased on further additions of acid. No odor of free bromine could be detected and no trace could be obtained on extraction with chloroform or ether. The first sample, after evaporation with excess hydrobromic acid and recrystallization still turned pink on addition of acid as did another sample of calcium bromide prepared from the pure carbonate and hydrobromic acid. Likewise the same phenomenon occurred with the solutions of lithium, strontium, and magnesium bromides, the color in the last two being less marked and unaccompanied by noticeable fuming. Since those measurements on the solutions which showed marked fuming are necessarily somewhat less reliable, they are therefore included in parentheses in Table 11. The appearance of the pink coloration is evidently not due to the presence of free bromine. It may possibly be connected with the ionic strength of the cation because the intensity of color as well as of fuming was most pronounced in those solutions containing the strongest cation. More precisely, the intensity of color follows the same sequence as the solubility of these salts which, incidentally, are all hydrated. summary The results of this investigation may be summarized as follows: I. The solubilities a t 25'C of the bromides of potassium, sodium, ammonium, lithium, barium, strontium, calcium, and magnesium in pure water and in the presence of hydrobromic acid in amounts up to about 60 mol per cent have been determined for the first time. 2, Saturated solutions of lithium, calcium, strontium, and magnesium bromides develop a decided pink color, which is not due to the liberation of bromine, on addition of hydrobromic acid. Furthermore, the more acid solutions of these salts fume strongly of hydrogen bromide. Houston, Texas.
