To show that hydrogen gas is evolved by the action of acid on metals.
Acids react with certain metals to form salt and hydrogen gas.
Metal + acid → salt + hydrogen
This broad reaction can be remembered using the abbreviation “M.A.S.H”. Metal is placed in acid and shrinks as the chemical process consumes it. At that exact moment, gas bubbles may be seen. The bubbles formed during the reaction are made of hydrogen gas. Because hydrogen is combustible, this may be shown using a burning splint. A minor explosion happens when the burned splint is placed in the test tube containing hydrogen gas, producing a squeaky pop sound. This demonstrates the presence of hydrogen. For example, Magnesium reacts with dilute hydrochloric acid to form magnesium chloride and hydrogen.
Mg + 2HCl → MgCl2 + H2 (gas)
Similarly, Al + 2HCl &rarr AlCl3 + H2 (gas)
But Copper does not react with hydrochloric acid but reacts with sulphuric acid.
CuO + H2SO4 → CuSO4 + H2O
Metals react with sodium hydroxide to produce hydrogen gas. For example, zinc reacts with sodium hydroxide to give sodium zincate.
Zn + 2NaOH →Na2ZnO2 + H2
Some metals have high reactivity. This implies they can readily participate in chemical processes that produce new compounds. Other metals are highly inactive and do not readily participate in chemical processes. If we arrange the metals in reactivity, from most reactive to least reactive, we get a list known as the reactivity series.