Question

Assertion(A): copper reacts with conc. Nitric acid
Reason(R): Conc. Nitric acid reacts as it's a powerful oxidizing agent.​

Answer 1

Answer:

Copper is oxidized by conc.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)

Explanation: