Question

How can you show that a chemical reaction involves evolution of gas?

Answer 1

If gas is evolved in a reaction, then bubbles of gas will be seen if one of the reactants is in liquid form.

The evolution of gas in a reaction can also be shown by the following experiment.

Procedure:

• Take a few zinc granules in a conical flask.
• Add dilute HCl or H₂SO₄ into the flask.
• Observe bubbles of hydrogen gas forming around the zinc granules.
• If a burning matchstick is brought near the mouth of the flask, then it burns with a pop sound, indicating the evolution of hydrogen gas.
• Chemical reaction:

$\mathrm{Zn}+2\mathrm{HCl}\to {\mathrm{ZnCl}}_2+{\mathrm{H}}_2$