Question

Reaction of zinc with dilute nitric acid gives ________ gas.

Answer 1

When the zinc metal reacts with dilute nitric acid it produces gases which is an oxide of nitrogen. The oxidation number of nitrogen in that oxide is +1 and it is a colorless gas.

Complete step by step answer:
Zinc is an active metal that belongs to the d-block.
Nitric acid is a strong acid and has a formula $HN{{O}_{3}}$.
Zinc reacts with nitric acid in three forms:
(i)- Hot dilute nitric acid
(ii)- Cold dilute nitric acid
(iii)- Concentrated nitric acid

(i)- Hot dilute nitric acid: When the zinc reacts with hot dilute nitric acid to form nitrous oxide gas. The formula of nitrous oxide is ${{N}_{2}}O$. Along with nitrous oxide, it also forms zinc nitrate. The reaction of zinc with hot dilute nitric acid is given below:
$4Zn+10HN{{O}_{3}}\to \underset{zinc\text{ }nitrate}{\mathop 4Zn{{(N{{O}_{3}})}_{2}}}\,+5{{H}_{2}}O+\underset{nitrous\text{ }oxide}{\mathop {{N}_{2}}O}\,$

The oxidation state of nitrogen in nitrous oxide is +1. It is a colorless neutral gas with a sweet odor.
(ii)- Cold dilute nitric acid: When the zinc reacts with cold dilute nitric acid it forms ammonium nitrate. The formula of ammonium nitrate is $N{{H}_{4}}N{{O}_{3}}$. It forms zinc nitrate also. The reaction is given below:
$4Zn+10HN{{O}_{3}}\to \underset{zinc\text{ }nitrate}{\mathop 4Zn{{(N{{O}_{3}})}_{2}}}\,+\text{ }3{{H}_{2}}O\text{ }+\underset{ammonium\text{ nitrate}}{\mathop N{{H}_{4}}N{{O}_{3}}}\,\text{ }$

(iii)- Concentrated nitric acid: When zinc reacts with concentrated nitric acid it forms nitrogen dioxide gas. The formula for nitrogen dioxide is$N{{O}_{2}}$. The nitrogen has +4 oxidation state in nitrogen dioxide. The nitrogen dioxide is a brown gas and it is acidic. The reaction of zinc with concentrated nitric acid is given below:
$Zn+4HN{{O}_{3}}\to \underset{zinc\text{ }nitrate}{\mathop 4Zn{{(N{{O}_{3}})}_{2}}}\,\text{ }+\text{ }2{{H}_{2}}O\text{ }+\underset{nitrogen\text{ }dioxide}{\mathop N{{O}_{2}}}\,$
Hence, with dilute nitric acid zinc forms nitrous oxide gas${{N}_{2}}O$.

Note: With hot dilute nitric acid not only zinc but magnesium also gives nitrous oxide. With concentrates, nitric acid magnesium, bismuth, and lead also give nitrogen dioxide gas.