Question

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

Answer 1

Hydrogen gas is usually liberated when an acid reacts with an active metal.

The reaction of dilute sulphuric acid with zinc metal to show the formation of hydrogen gas can be carried out as follows:

1. Take a few pieces of zinc granules in a boiling tube and add about 5 mL of dilute sulphuric acid to it (see figure).
2. We will observe the formation of gas bubbles on the surface of zinc granules.
3. Pass the gas formed through the soap solution in a trough (via a glass delivery tube). Gas-filled bubbles form in the soap solution and rise into the air.
4. Bring a burning candle near a gas-filled soap bubble. The gas present in a soap bubble burns with a pop sound (making a little explosion) (see figure).
5. Only hydrogen gas burns, making a pop sound. This shows that hydrogen gas is evolved when dilute sulphuric acid reacts with zinc metal (in the form of zinc granules).