(a) What happens when an acid reacts with a metal? Give the chemical equation of the reaction involved.

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

(a) Those metals which are above hydrogen in standard reduction potential series ($-ve{E}^0$ values) will liberate hydrogen gas on reaction with dil. acids

Eg. Zin with sulphuric acid.

For dilute acid, zinc sulfate and hydrogen gas at produced.

$Zn+H_{2}S{O}_4⟶ZnS{O}_4+H_2$

For concentrated sulphuric acid, zinc sulfate, Sulphur dioxide, and water are produced.

$Zn+conc{H}_{2}S{O}_4⟶ZnS{O}_4+S{O}_2+2H_{2}O$

(b) Hydrogen gas is usually liberated when an acid reacts with a metal.

Take a few pieces of zinc granules and add 5 ml of dilute $H_{2}S{O}_4$. Shake it and pass the gas produced into a soap solution. The bubbles of the soap solution are formed. These soap bubbles contain hydrogen gas.

$Zn+H_{2}S{O}_4⟶ZnS{O}_4+H_2\uparrow$

We can test the evolved hydrogen gas by its burning with a pop sound when a candle is brought near the soap bubbles.