Copper, Cu2+
Most common oxidation states: +1, +2
M.P. 1083o
B.P. 2582o
Density 8.92 g/cm3
Characteristics: Reddish-yellow, rather inactive metal. Dissolves readily in HNO3 and in hot, concentrated H2SO4.
Characteristic reactions of Cu2+:
The +2 oxidation state is more common than the +1. Copper(II) is commonly found as the blue hydrated ion, [Cu(H2O)4]2+.
Aqueous Ammonia:
Copper(II) ion reacts with stoichiometric quantities of aqueous ammonia to precipitate light blue Cu(OH)2. Some basic salts may also form.
The precipitate dissolves in excess ammonia to form a dark blue complex ion:
Sodium Hydroxide:
Sodium hydroxide precipitates copper(II) hydroxide:
The precipitate does not dissolve in excess sodium hydroxide unless the NaOH solution is very concentrated. However, the precipitate will dissolve upon addition of concentrated ammonia solution.
Potassium Ferrocyanide:
Potassium ferrocyanide precipitates red-brown copper(II) ferrocyanide from Cu2+ solutions:
This test is very sensitive. The precipitate is soluble in aqueous ammonia.
Note: Many metal ions form ferrocyanide precipitates, so potassium ferrocyanide is not a good reagent for separating metal ions. It is used more commonly as a confirmatory test.
No Reaction:
Cl-, SO42-