Question

iron and cooper react with nitric acid( write the following reaction)​

Answer 1

Answer:

Copper is a reddish-brown metal, widely used in plumbing and electrical wiring; it is perhaps most familiar to people in the United States in the form of the penny. (Although since 1983, pennies are actually made of zinc surrounded by a paper-thin copper foil to give them the traditional appearance of pennies.) Copper is oxidized by concentrated nitric acid, HNO3, to produce Cu2+ ions; the nitric acid is reduced to nitrogen dioxide, a poisonous brown gas with an irritating odor:

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

When the copper is first oxidized, the solution is very concentrated, and the Cu2+ product is initially coordinated to nitrate ions from the nitric acid, giving the solution first a green, and then a greenish-brownish color. When the solution is diluted with water, water molecules displace the nitrate ions in the coordinate sites around the copper ions, causing the solution to change to a blue color.

In dilute nitric acid, the reaction produces nitric oxide, NO, instead:

3Cu(s) + 8HNO3(aq) ——> 3Cu(NO3)2(aq) + 2NO(g) + 4H2O(l)

Answer 2

Reaction Equations

The equations for the two reactions that can take place are:

Cu + 4 HNO3 --> Cu(NO3)2 + 2 NO2 + 2 H2O, which produces nitrogen dioxide and

3 Cu + 8 HNO3 --> 3 Cu(NO3)2 + 2 NO + 4 H2O, which produces nitric oxide.

With the concentrated acid, the solution will first turn green, then greenish-brown, and finally blue once diluted with water. Either reaction is highly exothermic and releases energy in the form of heat.

Oxidation and Reduction

Another way to understand this reaction is by breaking it down into two half-reactions, one for oxidation (loss of electrons) and the other for reduction (gain of electrons). The half-reactions are: Cu --> Cu2+ + 2 e- , meaning that copper loses two electrons, and 2 e- + 4 HNO3 ---> 2 NO3 1- + 2 H2O, which shows that two electrons have been transferred to the products. The speed of this reaction depends on the surface area of the copper; copper wire will react more quickly than copper bars, for example.

Other Considerations

The solution changes color because of the water. Unlike the copper solid, the copper ions in solution can form a type of interaction called a coordination complex with the water molecules, and these complexes lend the solution a blue color. Mineral acids like hydrochloric acid do not oxidize copper in the same way as nitric acid because they are not strong oxidizing agents. Sulfuric acid, however, is a strong oxidizing agent. Under the right conditions, it will react with copper to release sulfur dioxide gas.

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