Determination of Strontium in the Presence of Calcium R. NORRIS SHREVE, C. H. WATKINS,’
AND
J. C. BROWNING2
Purdue University, Lafayette, Ind.
F
OR some years a study has been under way in these laboratories involving the preparation of various alkaline earth salts with the help of organic solvents (2, 4, 7 , 9, 10, 11, 14). For this work, accurate analysis of strontium salts in the presence of calcium compounds was necessary. Many methods have been suggested for the separation of strontium from calcium, which is made difficult by the small differences in the solubilities of the salts of the two metals. To increase the solubility the use of certain solvents other than water has been recommended. Browning (5) found that calcium nitrate is completely soluble in amyl alcohol while strontium nitrate is practically insoluble. Fresenius (6) separated the nitrates of barium and strontium from calcium by using a mixture of ether and ethyl alcohol. Rawson (8) separated calcium nitrate from strontium and barium nitrates by means of concentrated nitric acid, in which calcium nitrate is soluble. Treadwell and Hall (13) offer a procedure for the analysis of alkaline earth metals in which calcium nitrate is dissolved by absolute alcohol while the nitrates of barium and strontium remain undissolved.
nitrate were dissolved in water, 2 ml. of concentrated nitric acid were added, the solution was evaporated to dryness on a steam hot plate, the mass was allowed to cool, and 25 ml. of acetone were added. The acetone was allowed to remain in contact with the solid for one hour with occasional shaking. The undissolved portion was transferred to a weighed Gooch crucible, washed with acetone, and weighed as Sr(NO&. The results are shown in Table 11. The following method, which proved convenient and accurate, was evolved from the above: A synthetic mixture of strontium chloride with calcium chloride and calcium sulfate was extracted with methanol, filtered, and made up t o exactly 250 ml. with distilled water. The extract contained strontium chloride and calcium chloride, since calcium sulfate is insoluble. Calcium sulfate was added t o the synthetic mixture because in the analysis for which this method was desired calcium sulfate was present. Fifty milliliters of the extract were pipeted into a 250-ml. beaker and warmed to 50’ C. on a steam hot plate, and 10 ml. of freshly prepared ammonium carbonate solution were added slowly. This converted the strontium chloride and calcium chloride into the corresponding insoluble carbonates which were left on a hot plate for 10 minutes, then allowed to cool. The mixed carbonates were filtered into a Gooch crucible, then dissolved in dilute nitric acid. This gave an aqueous solution of the mixed nitrates which was evaporated t o dryness on a steam hot plate. After cooling, 25 ml. of anhydrous acetone were added and left in contact with the mixed nitrates for one hour with occasional agitation. The acetone dissolved all the calcium nitrate and left the strontium nitrate, .quantitatively. The strontium nitrate was transferred to a weighed Gooch crucible, washed with more acetone, dried in an oven, and weighed.
TABLEI. SOLUBILITIES OF NITRATES OF CALCIUM AND STRONTIUM (Per cent of salt in solution at 25O C.) Solvent Sr(NOs)l Ca(NO8)z 0.02 52.0 Ethyl alcohol 0.02 36.5 Propyl alcohol 0.01 25.0 Isobutyl alcohol Amyl alcohol 0.003 13.3 0.02 58.5 Acetone
Ans and Siegler ( I ) present a comparison of the solubilities of the nitrates of strontium and calcium in different solvents. From their data, which were obtained from studies by Eidman (6) and are only semiquantitative in character, ethyl, propyl, isobutyl, and amyl alcohols and acetone may be selected as suitable solvents to use in the separation of calcium nitrate from strontium nitrate. The quantitative effects of these solvents are shown in Table I, taken from an article by Williams and Briscoe (IS).
TABLE111. SEPARATION OF STRONTIUM CHLORIDE FROM CALCIUM CHLORIDE (Using the procedure outlined above.
Calcium Nitrate Added Grams
Strontium Nitrate Recovered Grams
Recovery
1.5000 2.0000 1,0010 1.5001 2.0006
0.10 2.00 0.50 0.50 0.50
1.4981 1.9977 1.0008 1.4996 1.9999
99.88 99.89 99.98 99.97 99.97
1
1,000 1,000
0.500 0.500 0.500 1.000 1.000
The following are blanks.) Strontium Calcium Sulfate Recovery Centimoles % 1,000 1.000 1.000 1,000 1.000
99.7 99.9 99.7 99.9 99.8
Blanks run on synthetic mixtures according to the above procedure gave results varying from 99.7 to 99.9 per cent recovery, as detailed in Table 111.
%
Literature Cited Ans and Siegler, 2. physih. Chem., 82, 35 (1913). Browning, J. C., thesis, Purdue University, 1937. Browning, P. E., Am. J. Sci., 43,50 (1892). thesis, Purdue University, 1934. Crosby, J. D., Eidman, “Qualitative Angaben uber die Loslichkeiten,” dissertation, Giessen, 1899. Fresenius, A., Anal. Chsm., 32, 312 (1893). Pritchard, W.N.,thesis, Purdue University, 1935. Rawson, J . SOC.Chem. Ind., 16,113 (1897). Shreve, R. N., and Pritchard, W. N., IND. ENG.CHEM.,27,1488 (1935). Shreve, R. N., et al., U. S . Patent 2,030,659 (February 11, 1936). Toner, R. K.,thesis, Purdue University, 1936. Treadwell and Hall, “Analytical Chemistry,” 5th ed., Vol. I, “Qualitative Analysis,” New York, John Wiley & Sons, 1921. Williams, P. E.,and Briscoe, H. T., Chem. News, 145,177 (1932). Wright, J. S., thesis, Purdue University, 1936.
Because of the usual difficulty in making this separation, an outline of the procedure which the authors have used may be of interest. This is based on the observation of Williams and Briscoe ( I S ) , that a t 25” C. strontium nitrate is only 0.02 per cent soluble in acetone while calcium nitrate dissolves in acetone to the extent of 58.5 per cent. Since acetone appeared to be favored for the separation of calcium nitrate from strontium nitrate, quantitative data were obtained. Weighed amounts of strontium nitrate and calcium 2
Calcium Chloride Centimoles
1.000 1,000 1,000
TABLE 11. SEPARATION OF STRONTIUM NITRATE FROM CALCIUM NITRATE BY ACETONE Strontium Nitrate Taken Grams
Strontium Chloride Centimoles
Present address, Standard Oil Co. of New Jersey, Elizabeth, N. J. Present address, Commercial Solvents Corp., Charlestown, Mass.
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