# Why does a reaction with nitric acid produce nitrogen gas?

Mar 17, 2017

${\text{HNO}}_{3}$ is also known as nitric acid. Concentrated nitric acid will produce nitrogen gas when reacted with MOST metal instead of hydrogen gas

#### Explanation:

color(red)("Why does HNO"_3" produce nitrogen gas instead of hydrogen gas?"
Concentrated nitric acid (${\text{HNO}}_{3}$) is a strong oxidising agent. The hydrogen gas produced during its reaction with metal gets immediately oxidised to $\text{H"_2"O}$, hence no hydrogen gas is produced. Instead, it evolves nitric oxides such as $\text{NO"_2", NO}$ etc.

Take $\textcolor{b l u e}{\text{copper}}$ for example,

$\text{Cu(s) + 4HNO"_3"(aq)⟶Cu(NO"_3)_2"(aq) + 2NO"_2"(g) + 2H"_2"O(l)}$

color(red)("What metals react with HNO3 to form hydrogen gas?"

${\text{HNO}}_{3}$ (about 1% concentrated) doesn’t oxidise Mg and Mn a lot and so it reacts with them as you would expect an acid to react, releasing hydrogen.

Take $\textcolor{b l u e}{\text{magnesium}}$ for example,

$\text{Mg"+"2HNO"_3"⟶Mg(NO"_3)_2""+"H"_2}$