ABSTRACT
In the presence of excess aqueous ammonia, alkaline copper(II) solutions are blue. The intensity of the blue color can be used to estimate copper concentrations down to about 10 ppm Cu. Nickel also forms a blue-colored complex with ammonia which can be distinguished from copper by adding ~Fe(CN) 6 to the solution. About 10 ml of solution is made neutral or slightly acidic and t'.O ml of 10% ~Fe(CN) 6 is added with mixing. A reddish precipitate indicates copper and a greenish precipitate indicates nickel. A spot test for copper using cupron (2-hydroxy-1,2-diphenylethanone oxime) (1) is useful. A drop of a slightly acidic solution, suspected of containing copper, is placed on a piece of filter paper; then a drop of 10% sodium potassium tartrate is added to the first drop (this will prevent interference from other metals). Next, a drop of 5% cupron in alcoholic solution is added to the others. Finally, the filter paper is held over a solution of ammonia (1: 1). A green color on the filter paper indicates copper. The test is sensitive to about 2 ppm Cu.
