Question

Write a balanced equation for the reaction of copper with nitric acxid tp produce nitric oxide (NO). Predict whether this reaction would occur with more, or less concentrated nitric acid than equation (1) : Cu(s) + HNO3(aq) ---> Cu(NO3)2(aq) + NO2(g) +H2O(l)

Answer 1

Concentrated nitric acid (HNO3) oxidizes Cu metal to produce Cu2* ions; the HNO3 is reduced to nitrogen dioxide, a poisonous brown gas with an irritating odor: Cu(s) + 4HNO3(aq)>Cu(NO3)2(aq) 2NO2(g) + 2H20(l) When the copper is first oxidized, the solution is in more concentration, and the Cu2* product is initially coordinated to nitrate ions from the nitric acid, giving the solution intially green colour gradually changes togreenish-brownishcolor. When the solution is diluted with water, water molecules displace the nitrate ions in the coordinate sites around the copper ions, making the solution to change to a blue color. In dilute nitric acid, the reaction gives nitric oxide, NO, instead: 3Cu(s)8HNO3(aq)> 3Cu(NO3)2(aq) 2NO(g)4H20(U)