Question

Nature of $A{l_2}{O_3}$ (Aluminium oxide ) is :
A. Acidic
B. Basic
C. Amphoteric
D. Neutral

Answer 1

Hint: In following the trend we found that Acidity increases from left to right, ranging from strongly basic oxides on the left to strongly acidic ones on the right, with an amphoteric oxide (aluminium oxide, $A{l_2}{O_3}$) in the middle. An amphoteric oxide is one which shows both acidic and basic properties.

Complete step by step solution:

Aluminium oxide is an amphoteric oxide because it reacts with acids as well as bases and gives salts and water. Aluminium has electronegativity 1.5. The electronegativity difference between aluminium $(Al)$ and oxygen $(O)$ is small. Aluminium lies in group 13 in periodic table (electronegativity increases across a period). Aluminium oxide is insoluble in water and It is not reactive like sodium oxide and magnesium oxide.

Reaction with acid- When Aluminium oxide reacts with Hydrochloric acid it gives Aluminium chloride and water . Aluminium oxide contains oxide ions so react with dilute hydrochloric acid.
$A{l_2}{O_3} + 6HCl \to 2AlC{l_3} + 3{H_2}O$ (this reaction shows Basic nature )

Reaction with base - When Aluminium oxide reacts with Sodium hydroxide it gives sodium aluminate and water.
$A{l_2}{O_3} + 2NaOH \to 2NaAl{O_2} + {H_2}O$ (this reaction shows Acidic nature )

Note: When we write aluminium oxide reaction we get to know that it is reacting with acid as well as base so we conclude that it has amphoteric nature means it can react with both acid and base. Aluminium oxide is light, malleable, ductile, good conductor of electricity and heat. We come to know about the acidic and basic nature of any oxide only when we know that it is reacting with acid or base.