Question

Hydrogen gas is not evolved when metals react with dilute nitric acid​

Answer 1

Explanation:

Hydrogen gas is not evolved when a metal reacts with nitric acid. It is because HNO3 is a strong oxidising agent. It oxidises the H2 produced to water and itself gets reduced to any of the nitrogen oxides (N2O, NO, NO2). But magnesium (Mg) and manganese (Mn) react with very dilute HNO3 to evolve H2 gas.

Answer 2

Explanation:

When metals react with nitric acid hydrogen gas is liberated.

Nitric acid is a very strong oxidizing agent.

So , it oxidizes the hydrogen gas formed during the reaction to form water and an oxide of nitrogen ( NO,N2O,NO2 etc. ).

The reaction for it is:-

Zn+4HNO3→Zn(NO3)2+2NO2+2H2O

Exception:-

Magnesium and manganese react with very dilute nitric acid to liberate hydrogen gas.

The reaction for it is:-

Mg+2HNO3→Mg(NO3)2+H2