SEPARATION OF COPPER(I1) FROM CADMIUM(I1) IN QUALITATIVE ANALYSIS CLIFFORD C. BOYD pnd WILLIAM K. EASLEY East Tennessee State College, Johnson City
THEseparation of copper(I1) from cadmium(I1) is usually a trouble spot in the scheme of qualitative analysis. Since copper(I1) interferes with the identification of cadmium(II), most procedures suggest the use of some complexing agent. The cyanide method is
potentially hazardous; the separation of copper(I1) by tartrate is seldom satisfactorily complete to allow a clear-cut identification of cadmium(I1) as the yellow CdS. The procedure here suggested is based on the oh-
JOURNAL OF CHEMICAL EDUCATION
servation that copper(I1) ion is extracted selectively from solutions containing the ions in question by a solution of 8-hydroxyquinoline in chloroform. This makes use of the well-known fact that the Shydroxyquinoline chelate of copper(I1) ion is soluble in chloroform. This affords an additional opportunity to stress the value of chelating agents and the use of an immiscible solvent in extraction. The deep blue solution a t this point contains C U ( N H ~ ) ~and + + Cd(NH3)r++ plus an excess of NHB. To about 5 drops of the solution add 6 M HCl dropwise until the blue color is discharged. Adjust the solution t o a pH of about 6 (Hydrion paper) by the addition of 1 M NaC2Ha02and add about 1 ml. of saturated KC1 solution. Extract by shaking the solution for three minutes with an equal volume of 0.04 M 8-hydroxyquinoline in CHCI,. Centrifuge the mixture which may be frothy and separate by withdrawing the aqueous phase with a pipet. Discard the CHCla layer. To the aqueous phase, which is now free of copper ions, add 5 drops of 4 M NaOH and pass HIS into the solution. A yellow precipitate of CdS is formed.
VOLUME 35, NO. 8. AUGUST, 1958
Experiments have shown if a dark precipitate is obtained that other cations have been incompletely removed. Purification may be achieved by treating the precipitate with 5 drops of 4 M HzS04plus 5 drops of H20, then heating on a water bath for 1-2 minutes. Centrifuge and discard residue. Neutralize the solution with 4 M NaOH and saturate with H2S. Yellow CdS will precipitate. During the development of the method, it was determined that one extraction as described was adequate in all cases where the molar ratio of copper (11) ion t o cadmium(I1) ion was less than 6, provided that not more than 2 mg. of copper(I1) ion was present in the 5 drops of the sample. By this procedure it is possible t o detect much lower concentrations of cadmium(I1) ion than is normally present in the semimicro scheme. The authors would like to express their appreciation t o Shelton Thompson for his assistance in performing some of the routine experimentation required in this work.
