Question

A copper rod and Al rod are placed in conc. $HN{{O}_{3}}$ in separate containers. Which of the following observations are found after some time?
a.) Copper and aluminium rod continue to deteriorate at the same time.
b.) Copper rod continues to deteriorate while aluminium rod deteriorates initially then stops.
c.) There is no deterioration in either copper rod or aluminium rod.
d.) Aluminium rod continues to deteriorate while copper rod deteriorates initially and then stops.

Answer 1

Copper is a reddish- brown metal. It is widely used in plumbing and electrical wiring. Nitric acid is a powerful oxidizing agent, when it comes in contact with copper or aluminum a process takes place known as passivation.

Complete step by step answer:
Nitric acid reacts with copper, copper gets oxidized and produces the $C{{u}^{+2}}$ ions. After the production of copper ion nitric acid is reduced to nitrogen dioxide with is a poisonous brown has. Nitrogen dioxide has a very irritating odor.
The reaction involved in which nitric acid reacts with copper is given below:
$Cu(s)+HN{{O}_{3}}(aq)\to Cu{{(N{{O}_{3}})}_{2}}(aq)+N{{O}_{2}}(g)$

The balanced chemical reaction between nitric acid and copper is:
$Cu(s)+4HN{{O}_{3}}(aq)\to Cu{{(N{{O}_{3}})}_{2}}(aq)+2{{H}_{2}}O(l)+2N{{O}_{2}}(g)$

Due to the formation of a thin and reactive protective layer of aluminium oxide on the surface of aluminium metal it does not react with nitric acid.
If we use dilute nitric acid then aluminium will react with it and form aluminium nitrate, this is why it is important to look at the composition of the components. But if we take concentrated nitric acid more than 60 percent of the composition the result is completely opposite.
So, the correct answer is “Option B”.

Note: Nitric acid is produced by the reaction of nitrogen dioxide with water. The nitric acid formed by this reaction is usually oxidized again by the oxygen present in the air to create nitrogen dioxide. Nitric acid is used for producing fertilizer, making dyes etc.