Question

Why is hydrogen gas not evolved when most of the metals react with nitric acid?

Answer 1

Oxidizing agent: An oxidizing agent is a chemical substance that oxidizes other substances. It causes an increase in the oxidation state of a substance by losing electrons. It is also known as an oxidizer or oxidizer. For example, Halogens, Oxygen, and Hydrogen peroxide $\left({\mathrm{H}}_2{\mathrm{O}}_2\right)$.

Following are the reasons why hydrogen $\left({\mathrm{H}}_2\right)$ gas is not evolved when most metals react with nitric acid $\left({\mathrm{HNO}}_3\right)$:

1. Nitric acid is a strong oxidizing agent. When a metal reacts with Nitric acid, it oxidizes the Hydrogen to produce water $\left({\mathrm{H}}_2\mathrm{O}\right)$.
2. Nitric acid reduces itself to any of the Nitrogen oxides $({\mathrm{N}}_2\mathrm{O},\mathrm{NO})$ after oxidizing the Hydrogen.
3. For example, when Zinc $\left(\mathrm{Zn}\right)$ metal reacts with conc. nitric acid $\left({\mathrm{HNO}}_3\right)$, it forms nitrogen dioxide $\left({\mathrm{NO}}_2\right)$ gas, water and zinc nitrate $\left[\mathrm{Zn}{\left({\mathrm{NO}}_3\right)}_2\right]$.
4. The chemical reaction involved in this process:

$\underset{\left(\mathrm{Zinc}\right)}{\mathrm{Zn}\left(\mathrm{s}\right)}+\underset{\left(\mathrm{Nitric}\mathrm{acid}\right)}{4{\mathrm{HNO}}_3\left(\mathrm{conc}.\right)}\to \underset{\left(\mathrm{Zinc}\mathrm{nitrate}\right)}{\mathrm{Zn}{\left({\mathrm{NO}}_3\right)}_2\left(\mathrm{aq}\right)}+\underset{\left(\mathrm{Nitrogen}\mathrm{dioxide}\right)}{2{\mathrm{NO}}_2\left(\mathrm{g}\right)}+\underset{\left(\mathrm{Water}\right)}{2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{aq}\right)}$

1. Magnesium and manganese are exceptions. Hydrogen gas is released when they react with very dilute nitric acid.

Final answer: Nitric acid is a strong oxidizing agent; it oxidizes hydrogen to produce water and thus, hydrogen gas is not evolved.