Question

In the preparation of nitric acid from $ KN{O_3} $ concentrated hydrochloric acid is not used in the place of concentrated hydrochloric acid. Explain why?

Answer 1

Hint: Nitric acid is highly corrosive mineral acid with chemical formula $ HN{O_3} $ . It is also known as aqua fortis that means strong water and also named as spirit of niter. Nitric acid is very sensitive to thermal decomposition so to prevent it from light it is stored in brown glass bottles.

Complete Step by Step Answer
Nitric acid is prepared when potassium nitrate is treated with concentrated sulphuric acid and after their reaction it will give a mixture of nitric acid and potassium hydrogen sulphate.
 $ KN{O_3} + {H_2}S{O_4} \to HN{O_3} + KHS{O_4} $
Pure nitric acid will be obtained after performing the distillation process. As the vapor pressure of sulphuric acid is so low that it will not distill over. And relatively pure nitric acid will get prepared.
But in case of concentrated hydrochloric acid, the reaction will take place as:
 $ KN{O_3} + HCl \to HN{O_3} + KCl $
But this reaction will never go to completion because it has the reverse reaction as:
 $ HN{O_3} + KCl \to KN{O_3} + HCl $
And $ HCl $ is a gas which is highly volatile and evolves when that mixture is heated. In order to distill it it will always remain with nitric acid. That’s why concentrated hydrochloric acid is not used.
In simple words, hydrochloric acid is volatile acid and hence nitric acid vapor will carry hydrochloric acid vapor.

Note
Nitric acid is the primary reagent which is used for nitration. In nitration, the addition of a nitro group takes place in a chemical compound mostly to an organic molecule. And also some nitro compounds are shock-sensitive and thermally-sensitive explosives, some of them are stable enough to be used in munitions and demolition, and others are still more stable and used as pigments in inks and dyes. Nitric acid is also commonly used as a strong oxidizing agent.