Question

Question 40
Generally, when metals are treated with mineral acids, hydrogen gas is liberated but when metals (except Mn and Mg) are treated with ${\text{HNO}}_3$, hydrogen is not liberated. Why?

Answer 1

It is because ${\text{HNO}}_3$ is a strong oxidising agent. It oxidises the ${\text{H}}_2$ produced to ${\text{H}}_2\text{O}$. For example:

$\text{Cu}+4{\text{HNO}}_3⟶{\text{Cu(NO}}_3{)}_2+2{\text{NO}}_2+2{\text{H}}_2\text{O}$