Q.:-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?
Usually, hydrogen gas is liberated when an acid reacts with a metal. For example, let us take the reaction between zinc and sulphuric acid, as per the apparatus set-up shown in the adjacent figure.
A few pieces of zinc granules are taken in a test tube and about 5 mL of dilute H2SO4 is added. The gas produced is passed into a soap solution. We find that bubbles of soap solutions are formed. When a burning candle is brought near the soap bubbles, it burns with a pop sound which confirms the presence of hydrogen gas.
Zinc granules react with dilute sulphuric acid to for zinc sulphate and hydrogen gas according to the chemical; equation:
Zn + H2SO4 —> ZnSO4 + H2