81.

What happens when:
Hydrated alumina is treated with aqueous NaOH solution?

Write reactions to justify amphoteric nature of aluminium. 

How does aluminium react with:
(i) boiling water.
(ii) concentrated H₂SO₄
(iii) dilute nitric acid
(iv) concentrated HCl
(v) NaOH?

Show by the reactions that aluminium has a strong affinity for oxygen. 

Why does aluminium become passive when dipped in concentrated nitric acid?

Give reasons:
Conc. HNO₃ can be transported in an aluminium container. 

Give reasons:
A mixture of dilute NaOH and aluminium pieces is used to open drain.

Give reasons:
Aluminium alloys are used to make aircraft body.

Give reasons:
Aluminium utensils should not be kept in water overnight.

Give reasons:
Aluminium wire is used to make transmission cables.