Question

Generally, metals react with acids to give salt and hydrogen gas. Which of the following acids does not give hydrogen gas on reacting with metals (except Mn and Mg)?

• A. ${\mathrm{H}}_2{\mathrm{SO}}_4$
• B. $\mathrm{HCl}$
• C. ${\mathrm{HNO}}_3$
• D. All of these

Answer 1

The correct option is C

${\mathrm{HNO}}_3$

The explanation for the correct answer-

Option(C): Nitric acid

1. Hydrogen gas is not evolved when a metal reacts with Nitric acid because it is a strong oxidizing agent; it oxidizes the hydrogen to produce water.
2. When a metal reacts with Nitric acid, water is formed in the place of Hydrogen gas.
3. Because It reduces itself to any of the Nitrogen oxides after oxidizing the${\mathrm{H}}_2$ released to water.$\underset{\mathrm{Silver}}{\mathrm{Ag}\left(\mathrm{s}\right)}+\underset{\mathrm{Nitric}\mathrm{acid}}{2{\mathrm{HNO}}_3\left(\mathrm{aq}\right)}\to \underset{\mathrm{Silver}\mathrm{nitrate}}{{\mathrm{AgNO}}_3\left(\mathrm{ppt}\right)}+\underset{\mathrm{Nitrogen}\mathrm{dioxide}}{{\mathrm{NO}}_2\left(\mathrm{aq}\right)}+\underset{\mathrm{water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}$

The explanation for the incorrect answer-
Option(A) : Sulfuric acid(${\mathrm{H}}_2{\mathrm{SO}}_4$)

1. Sulfuric acid is also a strong acid but not compared with Nitric acid.
2. So, when it reacts with the metal, it can't further oxidize and produce

$\underset{\mathrm{Iron}}{\mathrm{Fe}\left(\mathrm{aq}\right)}+\underset{\mathrm{Sulfuric}\mathrm{acid}}{{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)}\to \underset{\mathrm{Hydrogen}}{{\mathrm{H}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Iron}\mathrm{sulfate}}{{\mathrm{FeSO}}_4\left(\mathrm{aq}\right)}$.

Option(B) : Hydrochloric acid ($\mathrm{HCl}$)

1. Hydrochloric acid is also a strong acid but not compared to Nitric acid.
2. So, when it reacts with the metal, it can't further oxidize and produce

$\underset{\mathrm{Zinc}}{\mathrm{Zn}\left(\mathrm{s}\right)}+\underset{\mathrm{Hydrochloric}\mathrm{acid}}{2\mathrm{HCl}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Zinc}\mathrm{chloride}}{{\mathrm{ZnCl}}_2\left(\mathrm{ppt}\right)}+\underset{\mathrm{Hydrogen}}{{\mathrm{H}}_2\left(\mathrm{g}\right)}$

Hence, Nitric acid is the only acid that does not produce Hydrogen gas but instead produces water when react with metal except $\mathrm{Mg},\mathrm{Mn}$