Question

Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?

Answer 1

Reaction of an acid with a metal:

• When an acid reacts with a metal, it forms a salt.
• Hydrogen which is in all the acids gets displaced and liberated as hydrogen gas.

$\mathrm{Acids}+\mathrm{Metals}\stackrel{}{\to }\mathrm{Salt}+\mathrm{Hydrogen}\mathrm{gas}$

Example:

• Hydrogen gas is produced when dilute $\mathrm{HCl}$ combines with zinc metal.

$\mathrm{Zn}\left(\mathrm{s}\right)+2\mathrm{HCl}\left(\mathrm{aq}\right)\stackrel{}{\to }{\mathrm{ZnCl}}_2\left(\mathrm{aq}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)$

Test for the presence of hydrogen gas:

• A lighted splint positioned near the mouth of a test tube ignites with a squeaky pop if hydrogen is present.