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?
[3 Marks]

Hydrogen gas is usually liberated when an acid reacts with a metal.
[0.5 Marks]


Take few pieces of zinc granules and add 5 ml of dilute ${\text{H}}_2{\text{SO}}_4$ and shake it. The gas produced is passed into a soap solution. The bubbles of soap solution are formed. These soap bubbles contain hydrogen gas. The reaction occurs as follows:

${\text{H}}_2{\text{SO}}_4\text{(aq)}+\text{Zn(s)}\to {\text{ZnSO}}_4\text{(aq)}+{\text{H}}_2(\uparrow )$
[2 Marks]
We can test the evolved hydrogen gas, as it burns with a pop sound when a candle is brought near the soap bubbles.
[0.5 Marks]