Question

Aluminium reacts with oxygen on heating to form Aluminium Oxide. But again its given that Aluminium reacts slowly with water and acids because of a thin outer layer (i.e. Al₂O₃). But if aluminium is not heated then how is it reacting slowly with water and acids? Aluminium utensils also will have a thin outer layer to prevent it from corrosion, how?

Answer 1

1) Aluminium when burnt in air forms aluminium oxide but it also reacts with oxygen at ordinary temperature to form a layer of aluminium oxide which prevents is further oxidation.
2) Aluminium doesnot react with cold water. It reacts with steam to form aluminium oxide and hydrogen gas.
3) Aluminium is a moderately reactive metal but lies above hydrogen in the reactivity series. So, it can displace hydrogen from dilute acids such as HCl. Therefore, it reacts with dilute dilute hydrochloric acid.

Aluminium utensils gradually develop a coating of aluminium oxide over their surface which prevent them from further oxidation and thus corrosion.