Gas Produced when an Acid Reacts with a Metal

When an acid reacts with a metal, hydrogen gas is produced. This is because metals are generally more reactive than hydrogen, and when they come into contact with an acid, they displace hydrogen from the acid, resulting in the release of hydrogen gas.

Example:
Let's take the reaction between hydrochloric acid (HCl) and zinc (Zn) as an example:
Zn + 2HCl → ZnCl2 + H2↑
In this reaction, zinc displaces hydrogen from hydrochloric acid, resulting in the formation of zinc chloride (ZnCl2) and the liberation of hydrogen gas (H2).

Testing for the Presence of Hydrogen Gas
To test for the presence of hydrogen gas, we can perform the following experiment:

Materials:
- Hydrochloric acid (HCl)
- Zinc granules (Zn)
- A test tube
- A delivery tube
- A gas jar filled with water
- A lighted splint

Procedure:
1. Take a small amount of zinc granules and place them in a test tube.
2. Add a sufficient amount of hydrochloric acid to the test tube, ensuring that the zinc granules are completely immersed in the acid.
3. Attach one end of the delivery tube to the test tube, making sure it is well-fitted.
4. Insert the other end of the delivery tube into a gas jar filled with water, ensuring that the end of the tube is submerged in the water.
5. Allow the reaction between the zinc and hydrochloric acid to take place for a few minutes.
6. As the reaction proceeds, hydrogen gas will be produced and will travel through the delivery tube into the gas jar, displacing the water.
7. Once the gas jar is filled with hydrogen gas, carefully remove the delivery tube from the water and place your thumb over the open end of the tube to prevent the escape of gas.
8. Invert the gas jar, ensuring that the open end is facing upwards.
9. Light a splint and bring it close to the mouth of the gas jar, slightly removing your thumb to allow the gas to come in contact with the flame.
10. If the gas is hydrogen, it will burn with a 'pop' sound and produce a small explosion.

Conclusion:
By performing the above experiment and observing the 'pop' sound produced when the hydrogen gas comes in contact with a flame, we can confirm the presence of hydrogen gas in the reaction between the acid and the metal.

The gas which liberate when an acid reacts with metal is hydrogen. Ex - when zinc reacts with dilute hydrochloric acid