ANALYTICAL CHEMISTRY
1416 cross checked with the ter Muelen and basic nitrogen procedure3 where applicable, and the analyses have been thoroughly consistent.
16)
LITERATURE CITED
(8)
(1) Foxwell, G. E.. Gus W o r l d (Coking Section), 64, 10 (1916~. (2) Holowchak, *J., Wear, G. E. C., and Baldeschwieler, E. L., AI., CHEM.,24, 1754 (1952). (3) Lake, G . R., I b i d . , 24, 1806 (1952). ( 4 ) Lake, G. R.. 1lcCutchan. P.. Van Meter, R., and Keel, J . C., Ibid., 23, 16.74 (1951).
(5) Moore, 11. T., lIoCutchan, P., and Young, D. A , , Ibid., 23, 1639 (7)
(9) (10)
(11)
(1951). Riley, J. P., Anal. Chiin. Acta, 9, 575 (1953). Russell, J. A., J . Biol. Chern., 156, 457 (1944). Snell. F. D., and Snell, C. T., "Colorimetric 1Iethods of -Inslysis," 2nd ed., vol. I, p. 658, April 1943, and 3rd ed., vol. 11, p. 818, 1949, Van Xostrand, Yew York. Thomas, P., Bull. soc. chim.,11, 706 (1912). Van Slyke, D. D., and Hiller, A., J . H i d . Chem., 102, 499 (1933). Wankat, C.. and Gatsis, J. G., . ~ . I L . CHEx., 25, 1631 (1953).
RECEIVED for review February 14. 1935. Accepted RIay 31, 1955
Precipitation of Barium Carbonate HARRY TEICHER' M o u n d Laboratory, M o n r a n t o Chemical Co., Miamisburg, O h i o
Critical studies of the several factors affecting the solubility of barium carbonate in analytical procedures have not been reported, I t was found that a dense, easily filtered, and easily washed product was obtained by hubbling carbon dioxide into an ammoniacal solution containing barium. Using radiochemical tracer techniques, the solubility loss of barium carbonate was determined with respect to final pH, alcohol concentration of the wash solution, addition of alcohol to the mixture after precipitation of the barium, and the presence of excess ammonium salts. The recommended procedure results in a solubility loss of 0.00015 gram of Imrium in 375 ml. of solution.
medium-porosity glass frit. Filtration was performed by connecting the exit tube to a bell jar which could be evacuated by gentle suction. .2beaker placed in the bell jar served to collect the filtrate and washings. Reagents. Barium nitrate. General Chemical Co. reagent grade barium nitrate was recrystallized twice from water and dried overnight at 110' C. I
,
T
HE quantitative precipitation of barium carbonate is recommended in various texts (8, 1 4 ) of qualitative analysis. .I quantitative barium carbonate precipitation has been recommended by Fresenius and Hintz (S), although the presence of ammonium salts, present in the procedure, have been reported as preventing complete precipitation ( 9 ) . .i survey of the literature ( 1 2 ) indicated that no critical study of the factors affecting the solubility of barium carbonate undei analytical conditions has been reported. Towley, Whitney. and Felsing ( I S ) have reported the solubility of barium carbonatr. in pure wat,er and in the presence of alkali chlorides. The soluhility in water of barium carbonate a t various pressures of carbon dioxide was investigated by Haehnel ( 5 ) . Semiquantitativt. estimations of the solubility of barium carbonate in the presencr of varying concentrations of ammonia, ammonium carbonate,: and ethyl alcohol have been published by Bray ( 2 ) . Sidyn.ic!i ( 2 6 ) has accepted the soluhility in r a t e r a t 18" C. as heing 8.ti mg. per liter. . This paper describes tests made to determine the solubilit>. loss (solubilit,y in mother liquor plus wash eolution) of barium carbonate formed by the int,roduction of carbon dioxide into an nmmoniacal solution containing barium followed by the addition of alcohol. The precipitate, is then washed with aqueous alcohol. The solubilit,y loss was investigated with respect to the final pH! the addition of alcohol to the reaction mixture after precipitation. the presence of excess ammonium salts, and the composition of the wash solution.
&SEL
Figure 1.
Reaction vessel
Barium-140. This material. carrier-free, vas obtained from Oak Ridge Sational Laboratory in dilute nitric acid and Kith a radiochemical purity greater than 9Syo. Two solutions were prepared from this material: One solution contained approximately 0.1 mc. per 0.3 ml. and the second solution, which was used in the preparation of counting standards, contained approximately 25,000 counts per 0.1 ml. ~~~
.
~
-
.~
~~
Table I.
Effect of Precipitation Time on Total Solubility Loss Alcohol Alcohol - Barium Lost, $7-
APPARATUS . \ Y U MATERIALS
Added, 1\11. 0 10 20
30 Present address, Inorganic Clieliiicalr Division, Monsanto Chemical Co.. P:Yrrrtt Station, Boston 49, .\lass.
II w
Apparatus. The reaction v e s ~ e lis illustrated in Figure 1. Iluring precipitation carbon dioxide was introduced through the !
m/ -
I
40
Concentration,
5%
0.0 4.4
8.5 12.2 15.6
Time, 30 min. 0.037 0.025 0.051
Time, 40 min. '
0,030 0.08R
0.036
0.051 0.040
0,028
0,050
V O L U M E 2 7 , N O . 9, S E P T E M B E R 1 9 5 5 Carbon Dioxide. The carbon dioxide Tvas obt,ained from the Pure Carbonic Corp., New York, N. Y. The gas was used directly from the cylinder without further purification. Ethyl alcohol. Absolute alcohol was used, although no special precautions were taken to maintain this grade. Shelf Reagents. Nitric acid, concentrated, and ammonium hydroxide, concentrated, were reagent grade chemicals supplied by the General Chemical Co. pH Paper. The p H measurements were made with Precision pR control paper supplied by the Precision Laboratories. Rossinovne, Ohio. The accuracy v a s f O . l to 0.2 unit. EXPER1MEN'r.AL
Initial Work. Exploratory tests using the standard procedures for precipitating barium carbonate produced a voluminous and gelatinous precipitate which clogged all filters used. This was caaused by the relatively large amount of barium used, about 3 grams, and the high supersaturation rondit,ion produced hy the :r.rnmonium carbonat,e-ethyl alcohol procrdurc.
A
0.120
0.100
1417 sel. The volume was a,djusted to 200 ml. and approximately 0.1 mc. of an equilibrium mixture of barium-140 and lanthanum-140 was added. The pH was adjusted to 9.5 by the addition of 10 ml. of concentrated ammonium hydroxide, and carbon dioxides was introduced for the appropriate time. KO effort was madr quantitatively to control the rate of flow of carbon dioxide 0tht.r than to avoid spattering. During precipitation, 3-ml. portioiis of itmmonium hydroxide were added a t 10-minute intervals to maintain an alkaline pH. The final p H was varied by adtliiig varying volumes of ammonium hydroxide. Varying quantities of ethyl alcohol were then added. The mixture was thoroughl!, mixed and allowed to stand 10 minutes before filtration. The mother liquor was filtered by gentle suction and the prec3ipit:itc. was washed. The combined filtrate and wash solution was acidified uith nitric acid and then evaporated to a volume of approximat#ely 50 ml. After cooling, the solution was transferred to a 100-nil. volumetric flask. Duplicate 25-m1. aliquots were transferred to a centrifuge tube, 10 mg. of carrier barium were added, :1nd barium sulfate was precipitated by the dropwise addition of R U I furic acid to the vigorously stirred solution. Stirring was continued for 1.5minutes and the precipitate vas centrifuged, washed, and mounted on slides for counting by proportional counting. The mounting procedure has been described by Ames arid coworkers ( 1 ) . Activity standards were prepared at the same time and by the same procedure. Duplicate slides usually agreed within 1 to 2% even a t rates as low as several hundred counts per minute. The barium-140 activity was differentiated from its shorter-lived daughter, lanthanum-140. by application of Kirhy'p ( f i ) differential decay equation. RESULTS
5
0,0601
0.0001 0
\
Effect of Precipitation Time. Table I shows the results obtained when precipitation was allowed to proceed for 30 and 40 minutes, to a final p H of 9.1, .whereupon varying quantities of alcohol were added, and the precipitate was washed with 100 ml. of water in 25-ml. portion%.
I
I
I
60 ALCOHOL CONCENTRATION WASH SOLUTION rkl
20
40
I
I
80 IN
100
Figure 2. Effect of composition of wash solution on solubility loss
a
m Oa0t
Initial efforts to improve the physical nature of the precipitat(> were directed to eliminating or minimizing the supersaturation Precipitation from homogenous solution was tried by hydrolyzing urea ( 4 , 15) or potassium cyanate (IO)in slightly acidic solution. of barium nitrate. The p H was raised slowly and carbonate ion was generated uniformly throughout the solution. The reactioii \+ith cyanate proved more satisfactory, producing large, easil? filtered, and readily washed crystals. However, precipitatiori was not complete in 2 hours a t elevated temperatures. When gaseous carbon dioxide was bubbled into an ammoniacal solution, the precipitate obtained was intermediate between th(* product of the standard procedure and that obtained from homogeneous solution. This was indicated by the relative volume+ and the settling and filtering characteristics of the piecipitate ?*loreundesirable filtering characteristics were observed with the carbon dioxide procedure when the initial p H RW too high, about I I , and when ethyl alcohol was present during the initial stages of precipitation. Addition of ethyl alcohol after precipitation was essentially complete, however, had no noticeable effect upon thr physical characteristics of the precipitate, but did make precipitation complete. PROCEDURE
\ solution was prepared containing 5.76 grams of barium riitrate in 150 ml. of water, 2.0 ml. of concentrated nitric acid was added, and the solution was transferred to the reaction ves
"
a
20 30 FINAL ALCOHOL CONCENTRATION
10
ph
Figure 3.
BY VOLUME)
Effect of addition of alcohol following precipitation
The dat'a appear to indicate that for a given alcohol concentmtion and a precipitation time of 30 minutes, some factor othrr than time affects the solubility loss. A s shown below, the crit,irnl factor appeared to be the composition of the wash solution. Effect of Composition of Wash Solution. The effect of alr~ohol rmcentration of the Rash solution on the solubility loss of barium rahonat,e is illustrated in Figure 2. The final pH, following a 30-minute precipitation tinir, was adjusted to 9.1, and 10 ml. of (.thy1 alcohol was added. It, was ohserved that four 28-3111. portions of wash solution were required to remove the ammonium d t s rompletely. I t is apparent that the rombined solubility loss is reduced by a factor of 10 by use of a 500/, (by volume) ;Iqueous-ethyl alcohol wash solution. This corresponds to a i'ecovery of 99.991yc of t,he barium. These results indicated the need for further study of the effect of alcohol addition to the mixture after precipitation. Effect of Addition of Alcohol After Precipitation. Figurt. 3
ANALYTICAL CHEMISTRY
1418
summarizes the observations made when varying amounts of ethyl alcohol were added to the reaction mixture after 30 minutes of precipitation time, the final p H being 9.1, and the precipitate being washed with four 25-ml. portions of 90% alcohol. The solubility loss becomes essentially constant when the ethyl alcohol concentration is about 20% by volume, and the recovery is 99.995 %. Effect of Final pH. Since the physical characteristics of the barium carbonate precipitate obtained depended to some extent on the p H of the solution, a study of the effect of final pH on the solubility loss was necessary in order to determine the most satisfactory final pH. The observations a t varying ethyl alcohol concentrations are illustrated in Figure 4. Precipitation proceeded for 10 minutes, and the product was u-ashed with four 25ml. portions of 90% ethyl alcohol. It is apparent that a sharp rise in the solubility occurs below pH 7 , and the depressing effect of alcohol has its greatest relative effect in this region. Above p H 10 the solubility loss a t 0 to about 20% alcohol becomes essentially the same.
Table 11. Effect of Excess Ammonium Nitrate Ammonium Nitrate Added, Grams 0 18 30
Barium Lost,
%
0.0046 0.015
50y0 alcohol when 3 grams of barium were precipitated as the carbonate. The procedure of Fresenius and Hinta ( 3 ) recommends 50 ml. and not only is a more voluminous precipitate produced, but a greater concentration of ammonium salts is present. The combined filtration and washing of the barium carbonate required 15 minutes in the apparatus described. The data also confirm previous reports on the solubilizing effect of ammonium salts on barium carbonate (9). This may account for Kolthoff’s ( 7 ) report that sodium carbonate was a more sensitive reagent for detecting barium ion than ammonium carbonate.
A NO A L W L ADDED 0 10rnl. ALCOHOL XJDED I: 5 0 m l . A L C W L ADDED
o,0601\\ 0.040
0.037
Effect of Excess Ammonium Salts. Several experiments were performed to determine the effect of excess ammonium salts on the solubility loss. Precipitation was performed as previously described, except that varying amounts of ammonium nitrate were added to the mixture before precipitation. I n all cases the final pH was adjusted to 9.1, more ammonia being required than was necessary in the absence of the salts. The data are summarized in Table 11. The results show that the presence of excess ammonium nitrate exerts a solubilizing effect on barium carbonate a t a given pH and alcohol concentration.
PH
Figure 4.
Effect of final pH
The production of crystalline barium carbonate by precipitation from homogeneous solution offers further evidence for the superiority of this technique in improving the physical characteristics of the precipitate. Further study of this procedure for barium should yield interesting results. LITERATURE CITED
RECOMMENDED PROCEDURE
Using the vessel described, or some modification thereof, the barium nitrate should be present in 200 ml. of solution. Add 10 ml. of concentrated ammonium hydroxide, stir thoroughly, introduce carbon dioxide for 30 minutes a t a rate such as to avoid spattering, and add 3 ml. of ammonium hydroxide to the solution after 10 and 20 minutes have elapsed. After the 30 minutes, add 10 ml. of ammonia, turn off the carbon dioxide, add 50 ml. of ethyl alcohol, mix, and allow to stand for 10 minutes. Filter the mother liquor and wash the precipitate with four 25-ml. portions of 90% ethyl alcohol. DISCUSSION AND CONCLUSIONS
The results have indicated the relative effects of final pH, alcohol concentration in the wash solution, the addition of alcohol after precipitation, and the presence of excess ammonium nitrate on the solubility loss of barium carbonate. Precipitation from solutions a t a high initial p H or containing alcohol, both of which decrease the solubility, produces a product with unfavorable filtering and washing characteristics. These observations are in accord with Von TVeimarn’s ( f 6) precipitation rules concerning the relationship between the physical nature of a precipitate and initial supersaturation, the latter depending upon the solubility. The solubility loss by the procedure recommended results in a loss of 0.5 mg. of barium carbonate per liter at 22” C., compared with Sidgwick’s (fd)value of 8.6 mg. a t 18” C. in water. These results indicate the need for more careful evaluation of solubility data under analytical conditions. Complete washing of ammonium salts required 100 nil. of
(1) dnies, D. P., Sedlet, J., Anderson, H. H., and Kohman, T. P., Natl. Xuclear Energy Ser., Division IV, vol. 14B, pp. 1700716, MoGraw-Hill, New York, 1949. (2) Bray, W. C., J . Am. Chem. Soc., 31, 635-7 (1909). (3) Fresenius, R., and Hinta, E., Z . angew. Chem., 9, 253 (1896). (4) Gordon, L., AXAL.CHEM.,24, 459 (1952). (5) Haehnel, O., J . prakt. Chem., 108, 187-93 (1924). (6) Kirby, H. W., A N ~ LCHEM., . 24, 1678 (1952). (7) Kolthoff, I. XI., Pharm. Weekblad, 57, 1229-34 (1920). (8) Soyes, A. A., and Bray, W.C., “Qualitative Analysis for the Rare Elements,” p. 237, hfacmillan, Kew York, 1948. (9) Prescott, A. B., and Johnson, 0. C., “Qualitative Chemical Analysis,” 6th ed., p. 204, Van Sostrand, New York, 1912. (10) Salutsky, XI. L., and Stites, J. G., “Radium-Barium Separation
Process, I. Enrichment by Fractional Precipitation,” U. S. Atomic Energy Commission, MLM-723, Mound Laboratory, Miamisburg, Ohio (April 1, 1951i: (11) Schwind, S. B., and Croxton, F. E., Radium, A Bibliography of Unclassified Literature,” U. S. Atomic Energy Commission, TID-363 (July 1950). (12) Sidgwick, N. V., “Chemical Elements and Their Compounds,” vol. 1 , p. 219, Oxford University Press, London, 1950. (13) Towley, R. W.,Whitney, B. A,, and Felsing, W. A,, J . Am. Chem. SOC.,59, 631-3 (1937). (14) Treadwell, F. P., and Hall, W. T., “Analytical Chemistry,” 9th ed., vol. 1, p. 275, Wiley, New York, 1937. (15) Willard, H. H., ANAL.CHEM.,22, 1372 (1950). (16) Von Weimarn, P. P., Chem. Recs., 2 , 217-42 (1925). RECEIVED for review December 23, 1954. hccepted M a y 17, 1938. Presented before t h e Division of Analytical Chemistry a t t h e 126th hleeting of t h e h f ~ ~ 1 cCHEMICIL . 4 ~ SOCIETY,New York, N. Y. Mound Laboratory is operated by Monsanto Chemical Co. for the U. S. Atomic Energy Commission under Contract Number AT-33-1-GEN-53.
