when aqueous ammonia is added slowly to solutions of common metal ions whose hydroxides are insoluble bases, the metal hydroxides precipitate. addition of excess aqueous ammonia dissolves the insoluble hydroxides of the metals of the cobalt, nickel, copper and zinc families (with the exception of Hg2+). for these families soluble ammine com]lex ions, [...........] , in which x is commonly 2, 4 or 6 and y is 1,2 or 3 are formed. for example if aqueous ammonia is added slowly to a solution containing Cu2+ ions, initially light blue, insoluble Cu(OH)2 precipitates.