Question

What do you see when concentrated nitric acid is added to copper?
A. Reddish brown coloured gas of hydrogen
B. Brown colored gas of hydrogen
C. Reddish brown colored gas of nitrogen
D. Brown colored gas of nitrogen

Answer 1

Hint: We need to know that nitric acid is a strong acid having the chemical formula, \[HN{O_3}\]. And nitric acid is a highly corrosive liquid which is used as a common laboratory reagent and it is used for the preparation of explosives and fertilizers as an important industrial chemical reagent. The nitric acid may cause serious burns, hence, it is a toxic liquid. Copper is a chemical element having the symbol, $'Cu'$ with atomic number \[29\] and it belongs to the transition metals.

Complete answer:
We need to remember that the Reddish brown coloured gas of hydrogen is not produced when concentrated nitric acid is added to copper. Hence, option (A) is incorrect.
There will not be a formation of brown coloured gas or hydrogen by adding nitric acid to copper. Hence, option (B) is incorrect.
The nitric acid is a colorless liquid and the colour of copper metal is pinkish – red. When these compounds are mixed together, there is a formation of copper nitrate and nitrogen dioxide. The copper nitrate is a blue colored solution and the nitrogen dioxide is a reddish – brown colored gas. Hence, we can say that, when concentrated nitric acid is added to the copper, there is a formation of reddish – brown colored gas of nitrogen. And this colour is responsible for the nitrogen present in the nitrogen dioxide. Let’s see the reaction,
\[Cu + 4HN{O_3}_{\left( {conc.} \right)} \to Cu{\left( {N{O_3}} \right)_2} + 2N{O_2}\]
Hence, option (C) is correct.
When concentrated nitric acid is added to copper, there will not be a formation of brown coloured gas. Hence, option (D) is incorrect.

So, the correct answer is “Option C”.

Note:
We need to know that when the copper is added to the concentrated nitric acid, the copper is oxidized by concentrated nitric acid and there is a formation of \[C{u^{2 + }}\] ions. And the nitric acid is reduced by copper and there is a formation of nitrogen dioxide and it is responsible for the poisonous gas which is reddish – brown in color with an irritating smell. There is also a formation of cupric nitrate.