# Question aee14

Mar 16, 2014

Copper is oxidized by concentrated nitric acid, HN${O}_{3}$, to produce $C {u}^{2 +}$ ions; the nitric acid is reduced to nitrogen dioxide, a poisonous brown gas with an irritating odor:

Cu(s) + 4HN${O}_{3}$(aq) ——> Cu(NO3)_2(aq) + 2N${O}_{2}$(g) + 2${H}_{2}$O(l)

When the copper is first oxidized, the solution is very concentrated, and the $C {u}^{2 +}$ 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) + 8HN${O}_{3}$(aq) ——> 3Cu(NO3)_2#(aq) + 2NO(g) + 4H2O(l)

b) the solution changes from colorless to red
c) a cloud of red toxic gas evolves around the beaker
d) copper is eventually completely consumed