Question

Generally, when metals are treated with mineral acids, hydrogen gas is liberated but when metals (except Mn and Mg), treated with HNO₃, hydrogen is not liberated, why?

Answer 1

Concentrated nitric acid is a very strong oxidising agent. When metals are treated with concentrated nitric acid the hydrogen gas that is produced during the reaction is further oxidised to water and thus hydrogen gas is not liberated.

`"Zn"("s") + 4"HNO"_3("conc".) -> "Zn"("NO"_3)_2 + 2"NO"_2("g") + 2"H"_2"O"("l")`