When conc. nitric acid is allowed to react with copper,what is the color change of the resulting solution and the ion responsible for this change?

Georgiana, where did you get your info from regarding HNO3?

You were not just "a little" wrong on many things. As someone myself who has synthesized countless liters of RFNA, WFNA, and even HNO4 as exists in the upper atmosphere I have to NIX your explanations.

First, the fuming grades of HNO3 give off vapors due to "vapor pressure" and the fumes seen are the acid vapors and not due to some reaction with (carbon?). Red fuming nitric acid fumes consist of some acid vapors and some NOx vapors...

Which brings me to the next point, the color yellow you see in concentrated nitric acid is because of the amount of dissolved NOx in the acid. It is another means by which HNO3 is graded. Even WFNA although a clear liquid starts to take on the yellow color upon decomposition. 

And of course your initial statement that HNO3 is also called "hard water" is quite wrong. Hard water is by definition simple water with high mineral content, which can precipitate from the water causing problems in water handling/treatment systems. Of course there are no minerals in HNO3 at all.

As far as the reaction with Cu, it raises the oxidative state of Cu to Cu2. This turns HNO3 solution to a green color while changing the undissolved Cu to a brown color which gets precipitated because HNO3 can oxidize way more Cu atoms than it can hold in solution. A reduction of Cu2 to the next lowest possible oxidative state can be done with aqueous ammonia giving off a vibrant blue colored solution (which is typical of most of the copper complex solutions.) Driving off the NH3 will leave the Cu1. Upon heating this will finally turn everything back into elemental Cu. Of course, much of this could have been done with a simply replacement reaction using any metal higher on the reactionary scale. 

So there is no "smoke" from concentrated NHO3, it is not called "hard water", is not yellow because of carbonization or anything like that, and your formulas and processes for synthesizing is all wrong (except the part about NO oxidizing In The Presence Of Oxygen and becoming nitrous dioxide). 

mkcapen1 | Student

Copper is a metal in color which most people associate with the copper penny or the material used for plumbing and wiring.  When copper interacts with concentrated nitric acid the result is called oxidation. 

"Copper is oxidized by concentrated nitric acid, HNO3, to produce Cu2+ ions"

"Cu(s)  +  4HNO3(aq)  ——>  Cu(NO3)2(aq)  +  2NO2(g)  +  2H2O(l)"

Once the concentrated nitric acid begins to oxidize the copper creates a brownish gas.  Gas bubbles are noted during the chemical reaction.  The reaction between the two is exothermic.  The material then turns a green color and then a brownish green color. When the copper is first oxidized, the solution is very.  The nitrate ions produce this reaction. 

giorgiana1976 | Student

Nitric acid is called also hard water.

Nitric acid is found in tiny amounts in the atmosphere and water rain, due to lightning, but it does not remain as such, combining with ammonia in the atmosphere, giving ammonium nitrate. Of the nitrates, the most important are: sodium nitrate (saltpeter of Chile), potassium (saltpeter from India) and calcium (saltpetre of Norway).

In laboratory, nitric acid is prepared from salts (natural nitrate) by treatment with hot concentrated sulphuric acid. The reaction takes place intwo stages:

I) NANO + H SO -> HNO + NaHSO

II) NANO + NaHSO -> HNO + Na SO

2NANO+ H SO -> 2HNO + Na SO

In pure state is colorless, pungent-smelling, with density 1.52. It dissolves in water, in any proportions, providing various concentrations of nitric acid. Nitric acid with a concentration of 96-98%, smokes in the air because it's vapors absorb moisture and give birth to a fog consisting of fine drops of liquid.

Concentrated nitric acid is colored yellow because dioxide carbon that is formed after partial decomposition in air, in presence of light and which remains dissolved in it:

4 HNO -> 4 NO + H 2 O + O ^

Therefore it should be stored in dark bottles and in darkness.Concentrated nitric acid, rich in NO, is called fuming nitric acid.

In aqueous solution ionizes as reversible reaction:

HNO + H O = [H O] + NO

This acid is one of the strongest, with a high degree of ionization.

With Nitric acid, copper reacts violently, forming copper nitrate, Cu (NO3) 2,  nitrogen monoxide which oxidizes instantaneously into nitrogen dioxide and  water. In the tube appears a suffocating gas, irritating, light reddish brown, due to nitrogen dioxide formed from the oxidation of nitrogen monoxide.

8HNO3 + 3Cu → 3Cu (NO3) 2 + 2NO + 4HNO3

2NO + O2 → 2NO2

revolution | Student

This process is known as oxidation state and it turns light reddish brown once reacted upon it. This reaction was caused upon by the nitrate ions present in the solution that cause this change.