Question

Which gas is liberated when dilute hydrochloric acid reacts with zinc metal? Write a balanced chemical equation for the reaction which takes place. How will you test this gas? Name a metal which produces the same gas just by reacting with cold water.

Answer 1

When dilute hydrochloric acid reacts with zinc metal, zinc will displace hydrogen from hydrochloric acid and form zinc chloride. It is accompanied by the release of hydrogen gas.

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

When we place a burning candle near the mouth of the test tube a pop-up sound is produced which confirms the presence of hydrogen gas in solution.
Sodium metal on reaction with cold water gives sodium hydroxide and hydrogen gas will evolve.

$2\mathrm{Na}+2{\mathrm{H}}_2\mathrm{O}\to 2\mathrm{NaOH}+{\mathrm{H}}_2$