Give reasons for the following
(a) No visible reaction occurs when aluminium is left in contact with `conc HNO_(3)`.
(b) The hydroxides of `Al` and `Fe` are insoluble in water. However, `NaOH` is used to distinguish one from another.
( c) Anhydrous `AlCl_(3)` cannot prepared by heating hydrated aluminium chloride.
(d) Aluminium vessels should not be cleaned with cleansing agent containing washing soda.
( e) Duralumin is used in aircraft industry.

Explanation

(a) Aluminium is rendered passive by `conc HNO_(3)` due to the formation of a layer of oxide `(Al_(2) O_(3))` on the surface.
(b) Aluminium hydroxide, `Al(OH)_(3)`, dissolves in `NaOH` whereas ferric hydroxide, `Fe(OH)_(3)`, is insoluble in `NaOH`.

(c ) Anhydrous `AlCl_(3)` cannot be prepared by heating hydrated `AlCl_(3)`, as on heating, `AlCl_(3). 6H_(2) O` gets hydrolysed to form `Al_(2) O_(3)`.
`2 AlCl_(3_.6H_(2) O rarr 2Al(OH)_(3) + 6 HCl`
`2Al(OH)_(3) rarr Al_(2) O_(3) + 3H_(2) O`.
(d) Aluminium vessel should not be cleaned with cleaning agent containing washing soda as `Na_(2)CO_(3)` undergoes hydrolysis to give `NaOH` and `Al` dissolves in `NaOH`.
`Na_(2) CO_(3) + 2H_(2) O rarr 2NaOH + CO_(2) + H_(2) O`
`2H_(2)O + 2Al + 2NaOH rarr 2NaAlO_(2) + 3H_(2)`.
(e) Duralumin is an alloy of aluminium whose composition is `95 % Al, 4% Cu, 0.5 Mg` and `0.5 % Mb`. It is light and tough. It has resistant to corroion and thus is used in aircraft industry.