NOTES ON ANALYTICAL PROCEDURE Preparation of Standard Cerate Solutions from Cerium Titration Residues FREDERICK R. DUKE AND K. G. STONE Princeton University, Princeton, N.J.
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OMPARED with permanganate and bichromate salts, cerium compounds are rare. Therefore, the procedure for recovery of volumetric cerium described below was developed and has been used in this laboratory for several months:
95%. The only common interferences with the recovery are scandium, yttrium, and the other rare earths and phosphate ion.
PROCEDURE.Tftration residues containing cerium are collected in a suitable vessel. After a sufficient amount of residue has accumulated, an excess of saturated oxalic acid solution is added, followed by sufficient concentrated sodium hydroxide to complete the precipitation of CeZ(Cz0&.9Hz0( 3 ) . The solution should remain distinctly acidic (0.5 to 1.0 M in H+) to prevent the precipitation of alkaline earths, irsn, and other alkali-insoluble ions ( 4 ) . After the precipitate settles, the major portion of the supernatant liquid is poured off, and the precipitate is transferred to a Buchner filter. If manganese or uranyl ions are known to be present in the solution, the precipitate is rzdissolved in the smallest possible volume of concentrated hydrochloric acid. Cerous oxalate is then reprecipitated by dilution to twenty times the volume of hydrochloric acid used. If neither manganese nor uranyl ions are present, the precipitate is washed on the Buchner with 0.1 M hydrochloric acid, followed by several water washes, and the material is dried with acetone or alcohol. I t is then transferred to a shallow evaporating dish and heated with the yellow-tipped flame of a MBker burner to ignite the oxalate to ceric oxide (1). The mass presently turns dark gray in color, and heating is continued with stirring until the gray color is supplanted by the buff of ceric oxide. This operation requires 10 to 15 minutes. The ceric oxide is now ready for use, and may be dissolved in sulfuric or nitric acid and made up to standard. The oxide should be allowed to digest with the concentrated a-id for one hour below the boiling point before dilution. Perchlorato cerate may be prepared by suspending the oxalate in 4 to 6 M perchloric acid and electrolytically oxidizing the material, following the method of Smith, Frank, and Kott (6).
(1)
LITERATURE CITED
Chase, W. S.,J. Am. Chem. SOC.,39,1576 (1917). (2) Hauser, O.,2.anal. Chem., 47,677 (1908). (3) Hauser, O.,and Wirth, F., Ibid., 47,389 (1908). (4) Lundell and Hoffman, “Outlines of Methods of Chemical Analysis”, p. 66, New York, John Wiley & Sons, 1938. (5) Smith, G. F., Frank, G . , and Kott, A. E., IND. EN& C E ~ M . . ANAL.ED., 12,268 (1940).
Crucible Holder for Use with Rubber Extraction Apparatus WM. E. BOYD, Inspection Board of United Kingdom and Canada, Nobel, Ontario, Canada
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ELIMIXATE the difficulty of attaching sintered-glass crucibles by wires or wire baskets to the condensers of Underwriters’ rubber extraction apparatus, the following method was devised. r------(
If phosphoric acid is present in the titration residues, the recovery is impractical, because excessive amounts of sodium hydroxide are required to neutralize the high acid concentration necessary when tetravalent cerium is used with phosphate, and because ceric phosphate is insoluble in acid solutions. DISCUSSION. The procedure has been tested on solutions containing F e + + + , Mn++, (U02)++,V+++++, Mo++++++,Cr+++, Cu++, GO++, As+++++,and Sb+++++. Small amounts of Mn++ ( 2 ) and (UO*)++ ( 2 ) are precipitated along with the cerous oxalate, and must be removed by the hydrochloric acid treatment if they would be likely to interfere in the use of the standard solution. I n no other case was the precipitate found to be contaminated. The percentage recovery of cerium following the procedure described is dependent upon several factors: the concentration of the cerium in the residues; the final acidity of the mother liquor; the nature of the contaminants, manganese and uranyl ion lowering the recovery since a reprecipitation is necessary; the completeness of conversion of the oxalate to the dioxide; and the temperature to which the oxide is heated during the ignition, high temperatures resulting in the formation of some refractory, insoluble ceric oxide. Careful control of the conditions, however, is unwarranted, since the percentage recovery under ordinary conditions seldom falls below 95%. SUMMARY. Sulfato, nitrato, and perchlofato cerate solutions may be prepared from titration residues containing cerium. The proredrire is simple and inexpensive, allowing a recovery of
Figure 1
Figure
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Figure 3
A 5-mm. glass rod is bent as shown in Figure 1, where spaces between parallel lines represent 1-cm. distances. The bent glass rod, dropped into a 400-ml. flask, assumes the position shown in Figure 2. When a sintered-glass crucible is then inserted, the bottom edge exerts a slight pressure on the rod a t A , Figure 2, causing it to swing around and thus support the crucible as shown in Figure 3. After extraction the crucible is easily lifted out with metal forceps and the rod washed with a small amount of the extracting solvent. 221
