Ramesh Chandra D. A.
V. College
Rapid Detection of Cations of Copper Group
Jullundur, Punjab, India
As an alternative to the conventional cation Group I1 separat,ion and suhsequent schematic analysis, the following proposal permits rapid detection of the ions normally present in the copper subgroup. The procedure is based on the following evidence: Mercury, from an arid solution, is deposited on a strip of copper foil after brief contact;' whereas arsenic, antimony, and bismuth deposit rery slowly. Precious metals interfere. Of the phosphates o f mercury, lead, bismuth, copper, and cadmium, only that of bismuth is sparingly soluble in dilute mineral acids.? As little as 20 micrograms of bismuth is detectable in 5 N nitric acid. An excess of concentrated ammonium hydroxide precipitates lead and bismuth iuid complexes copper and cadmium as tetrammines. Sodium dithionite (Ka&Od) reduces copper salts to metallic copper in ammoniacal solut,ion.3.4
' GASTON,CHARLOT,ET AL., ,'Rapid Detection of Cations," 2nd ed., Chemical Publishing Co., Inc., New York, 1954, p. 30. VOGEL,A. I., "Macro and Semimicro Qualitative Inorganic Analysis," 4th. ed., Longmans, Green 61 Co., Inc., London, 1954. 3~ -. ,rn. -2 -x-. VOGEL,A. I., o p . cil., p. 415. 'CLARK, R. E. D.,A X D XEULLE.R. G., J. CHEM. EDUC., 36,393 (1959).
Procedure The sample should be homogeneous and contain approxiand Cd+*ions. mately 10 mg each of Hgt2, Pbt2, Bits, CCU+~, Mweury: After the removal of the Group I cations, place one drop of the slightly acidified sample solution on a strip of polished copper foil. After several seconds, ruh the spot under water. A white amalgam indicates Hg. Lead, Bismuth, Copper, and Cadmium: Precipitate the ions of Group I1 with H2S or thioscetamide. Separate, by conventional means, the Group I1 precipitate into the copper and arsenic subgroups. Treat the copper subgroup (as sulfides) with 2W25 drops of 5 N HNOa, warm, and centrifuge. Discard any residue. To 6 drops of the centrifugste add 2-3 drops of 2 N (NH,)nS04. A white precipitate shows the presence of Pb. To 6 drop8 of the centrifugate add 2 drops of 5 N HNOs and 2-3 drops of 1 N (NH,),HPOc. A white precipitate shows the presence of Bi. Add concentrated ammonium hydroxide in excess to the remainder of the eentrifugate. Centrifuge and discard the residue. If the ammoniacal c~ntrifugateis blue, copper i~ present. The presence of copper is confirmed by adding 5 N acetic acid to 6 drops of deep blue centriiugate until the color changes to a light blue; followed by 2 drops of 0.5 N potassium ferrocyanide. A red-brown precipitate shows the presence of Cu. To 6 drops of the ammoniacal centrifugate add about 25 mg of Na&O. if copper is present. Boil, centrifuge, and discard the residue of metallic copper. Repeat the addition of NalSIOl if blue color remains. To the clear or yellow centrifugate add Has, or thioacetamide (followed by warming). A yellow precipitate shows the presence of Cd. An excess of Na*SnO
