Question

What happens when a piece of aluminium metal is added to dilute hydrochloric acid?
A. Aluminium displaces hydrogen
B. Aluminium chloride is formed along with dilute hydrochloric acid
C. Hydrogen gas is evolved
D. No reaction

Answer 1

Hint: The reaction between aluminium and dilute hydrochloric acid will result into a gaseous and an aqueous product. Now that, you have this information, try and figure out what each of these products could be.


Complete step by step solution:
We know that Aluminium is a malleable, light, silvery-white metal. It is a good conductor of electricity and is also amphoteric in nature i.e. it can react with both acids and bases. When aluminium is combined with an acid, it results in a typical single displacement reaction, forming an aluminium salt and a gaseous hydrogen.
So, here when aluminium reacts with dilute hydrochloric acid (an acid) at room temperature, the metal dissolves in hydrochloric acid, forming aluminium chloride and hydrogen gas. This reaction is irreversible in nature, as the final products will not react with each other. This type of reaction is known as oxidation-reduction reaction.
Now, let us see how this reaction would proceed step by step:
Aluminium acts as the reducing agent, losing its electrons:
$A{{l}^{0}}+3e\to A{{l}^{3+}}$
Cations of hydrochloric acid take these electrons and are reduced to molecular hydrogen:
$2{{H}^{+}}+2e\to H\uparrow $
So, the complete reaction will be like:
$2A{{l}^{0}}+6{{H}^{+}}\to 2A{{l}^{3+}}+3{{H}_{2}}\uparrow $
In molecular form, the reaction will be like,
$2Al+6HCl\to 2AlC{{l}_{3}}+3{{H}_{2}}\uparrow $
So, aluminium is displacing hydrogen to form aluminium chloride and hydrogen gas is also formed.

Hence, both the option A and C are correct.


Note: This reaction will not take place as soon as aluminium is added to the hydrochloric acid solution. This happens because aluminium pieces are protected by a layer of aluminium oxide. So, hydrochloric acid will take some time to eat this protective layer, but once that happens, the reaction will proceed vigorously.