Question

Why does a reaction with nitric acid produce nitrogen gas?

Answer 1

`"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 (`"HNO"_3`) is a strong oxidising agent. The hydrogen gas produced during its reaction with metal gets immediately oxidised to `"H"_2"O"`, hence no hydrogen gas is produced. Instead, it evolves nitric oxides such as `"NO"_2", NO"` etc.

Take `color(blue)("copper")` for example,

`"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?"`

`"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 `color(blue)("magnesium")` for example,

`"Mg"+"2HNO"_3"⟶Mg(NO"_3)_2""+"H"_2"`