FREE ESSAY ON COPPER IN NITRIC ACID

COPPER IN NITRIC ACID

3 Cu + 8 HNO3 --* 3 Cu (NO3)2 + 2 NO + 4 H2O
The balanced equation seen on the top is what you attain when you place copper metal in
concentrated nitric acid. In this process the identifiable characteristics of the metal
will be completely changed and a new substance, cupric nitrate, will be formed. Copper
forms two series of chemical compounds: cuprous, and cupric. Cuprous compounds are easily
oxidized to cupric, in many cases by simple exposure to air; cupric compounds are stable.
When nitric acid is added to copper the copper forms a cupric compound, one of the two
forms. Copper is flexible, ductile, and a good conductor of heat and electricity (second
only to silver in electrical conductivity). Copper has low chemical reactivity. It slowly
forms a greenish surface film in moist air. The greenish film is called patina it is
usually a mixture of carbonate, sulfate, hydroxide, and oxide. This coating protects the
metal from further attack. A moderately accurate separation exists between those acids
that can be handled by copper and those that cannot. In general, non-oxidizing acids such
as acetic, sulfuric, hydrochloric, phosphoric, and similar acids cause little damage.
However copper wears away rapidly in oxidizing acids such as nitric and chromic acids.
Oxidization in acids generally requires the presence of oxygen or some other oxidizing
agent in the solution. In other words, Cu is stable in almost all-acid conditions.
However, copper oxides dissolve in acid. Therefore, copper is not resistant against
oxidizing acids or against acid + oxygen, like nitric acid. Nitric Acid, colorless,
acidic liquid that has the chemical formula HNO3, Medieval alchemists called it aqua
fortis strong water. Nitric acid is made by the action of sulfuric acid on sodium nitrate
it is also made by the catalytic oxidation of ammonia. It rapidly attacks copper and
copper base alloys. Highly concentrated nitric acid is an exceptionally strong oxidizing
agent and therefore destroys most organic materials very rapidly. The concentrated nitric
acid used contains about 71 percent HNO 3 the rest is water. Nitric acid plus copper
gives nitric oxide in an exothermic reaction. When the copper metal, usually a penny, is
added to the colorless nitric acid in a flask the solution turns yellow and then starts
turning a lime green and the green gets darker and darker until its teal and then it
becomes a dark blue. While the copper is changing a large amount of red-brown gas is
formed. The air being displaced by the gas formation can be seen bubbling through the
water. The flask gets very warm. When enough gas is formed, it bubbles through the water.
The gas that makes it to the top is poisonous and is a red-brown color. The gas in the
flask begins to cool and therefore reduces. As the pressure inside the flask decreases,
the outside air pressure begins to push the water back toward the original flask. In
addition, the red-brown gas dissolves in the water. Eventually, the water rushes into the
flask, the red-brown gas disappears as it is dissolved. The blue-green color of the
solution is due to the copper ion in copper (II) nitrate, Cu (NO3) 2 and the red-brown
fumes are nitrogen dioxide, NO2. The solution is highly acidic.