Question

On photochemical decomposition of \[{\text{HN}}{{\text{O}}_3}\] the products are:
A.\[{\text{NO and }}{{\text{O}}_2}\]
B.\[{\text{N}}{{\text{O}}_2}{\text{ and }}{{\text{O}}_2}\]
C.\[{{\text{N}}_2}{{\text{O}}_4}{\text{ and N}}{{\text{O}}_2}\]
D.\[{{\text{N}}_2}{{\text{O}}_5}{\text{ and N}}{{\text{O}}_2}\]

Answer 1

Hint: Photochemical decomposition reactions are those in which compound is broken down with the help of sunlight. On photochemical decomposition of nitric acid, oxygen, nitrogen oxide and water is produced.

Complete answer:
\[{\text{HN}}{{\text{O}}_3}\] is known as nitric acid. It is a strong oxidizing agent. The photochemical decomposition of nitric acid produces oxygen, nitrogen dioxide \[{\text{N}}{{\text{O}}_2}\] and water, the reaction is as follow: \[4{\text{HN}}{{\text{O}}_3}\xrightarrow{{{\text{sunlight}}}}4{\text{N}}{{\text{O}}_2} + 2{{\text{H}}_2}{\text{O}} + {{\text{O}}_2}\] . The 4 moles of nitric acid broken down into 4 mole of nitrogen dioxide , 2 mole of water and 1 mole of oxygen. The photochemical decomposition of nitric acid is an oxidation reaction where nitric acid gets oxidized. The reaction may give rise to some non negligible variations in the vapour pressure above the liquid because the nitrogen oxides produce dissolve partly or completely in the acid. The nitrogen dioxide produced gives yellow color and remains dissolved in nitric acid left. Due to this dissolved nitrogen oxide in nitric acid, it gives off reddish brown vapours when exposed to air as when there is no nitrogen oxide in the acid, such acid produces white fumes when exposed to air.

Thus, the correct option is B.

Note:
The products formed in the photochemical decomposition of nitric acid are similar to that of products formed when anhydrous acid is heated in exhausted tubes to \[{100^o}{\text{C}}\] in the dark for some hours. According to observations, light in this process appeared to act only on the vapour of the acid and not on the liquid.