# What gas is released when acid added to a metal?

May 10, 2017

Depends on what acid and what metal...

Two acids that are often reacted with metals are ${\text{HNO}}_{3}$ and $\text{HCl}$. The former follows the $\boldsymbol{{\text{NO}}_{3}^{-}}$ reduction

$\text{NO"_3^(-)(aq) + 4"H"^(+)(aq) + 3e^(-) -> "NO"(g) + 2"H"_2"O} \left(l\right)$

and the latter from the Standard Hydrogen Electrode

$2 {\text{H"^(+)(aq) + 2e^(-) -> "H}}_{2} \left(g\right)$.

If and only if a reaction occurs, then either ${\text{H}}_{2} \left(g\right)$ is released from reaction with $\text{HCl} \left(a q\right)$, or $\text{NO} \left(g\right)$ is released from reaction with ${\text{HNO}}_{3} \left(a q\right)$.

But you must decide which acid you refer to...

CHALLENGE: Which of the following is dissolved by ${\text{HNO}}_{3}$ but not $\text{HCl}$?

• $\text{Au}$
• $\text{Ag}$
• $\text{Fe}$