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Schematic Group Classification of Cations

Add dilute hydrochloric acid to the cold original soln as long as any ppt. forms. Centrifuge.
Residue group 1 Silver gp. AgCl - white Hg2Cl2 - white PbCl2 - white	Centrifugate gp 1. Heat to boiling and add 30% thioacetamide until pptn is complete. Centrifuge.
	Residue group 2 (a) Copper gp PbS - black HgS = yellow, going black Bi2S3 - shinihg black CuS - black CdS - yellow (b) Arsenic gp. AS2S3 - yellow Sb2S3 - yellow Sb2S5 - orange	Centrifugate gp 2. Evaporate the soln. to 1 ml.Add 1 drop conc. nitric acid and boil. Add xs. solid NH4Cl and then conc. ammonia until alkaline. Boil gently, cool under tap, and centrifuge.
		Residue gp 3 Iron gp. Fe(OH)3 - reddish Cr(OH)3 - pale green MnO2 - brown	Centrifugate gp 3. Add a few more drops of ammonia, then add thiocetamide and ammonium chloride. Centrifuge.
			Residue gp 4 Zinc gp. MnS - pink ZnS - white NiS - black CoS - black	Centrifugate gp 4. Evaporate to 1 ml, add ammonium carbonate soln. and ammonia, warm, stand awhile, then centrifuge.
				Residue gp 5 Calcium gp. BaCO3 - white CaCO3 - white SrCO3 - white	Centrifugate gp 5 Alkali gp. Na; K; Mg; Test original soln. for NH4+ by boiling with NaOH

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Dhanlal De Lloyd, Chem. Dept, The University of The West Indies, St. Augustine campus
The Republic of Trinidad and Tobago.
Last Update: February 2004.