Why does a reaction with nitric acid produce nitrogen gas?

1 Answer
Mar 17, 2017

Answer:

#"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"#