11.22. Give reasons:

(i) Conc. HNO₃ can be transported in aluminium container.
(ii) A mixture of dilute NaOH and aluminium pieces is used to open drain.
(iii) Graphite is used as lubricant.
(iv) Diamond is used as an abrasive.
(v) Aluminium alloys are used to make aircraft body.
(vi) Aluminium utensils should not be kept in water overnight.
(vii) Aluminium wire is used to make transmission cables.

<p><strong> (i)</strong> Al reacts with conc. HNO₃&nbsp;to form a very thin film of aluminium oxide on its surface which protects it from further reaction. That is why conc. HNO₃ can be transported in aluminium container.<br>2Al (s) + 6HNO₃ (conc.) → Al₂O₃ (s) + 6NO₂ (g) + 3H₂O (l)</p><p><strong> (ii)</strong> NaOH reacts with Al to evolve H₂&nbsp;gas. Thus, the pressure of the gas produced can be used for opening or cleaning clogged drains.<br>2Al (s) + 2NaOH (aq) + 2H₂O (l) → 2NaAlO₂ (aq) + 3H₂ (g)</p><p><strong> (iii)</strong> Graphite has layered structure which are held by weak van there Waals forces. Thus, graphite cleaves easily between the layers, therefore it is very soft and slippery. That is why it</p><p>is used as lubricant.</p><p><strong> (iv)</strong> Diamond is used as anabrasive because it is an extremely hard substance.</p><p><strong> (v)</strong> Alloys of aluminiumis used to make aircraft body due to some of its property like toughness, lightness and resistant to corrosion.</p><p><strong> (vi)</strong> Generally, aluminium metal does not react with water quickly but, when it is kept overnight, it reacts slowly with water in presence of air.<br>2Al (s) + O₂ (g) + H₂O (l) → Al2O₃ (S) + H₂ (g)<br>a very small amount of (in ppm) Al³⁺&nbsp;produced in the solution is injurious to health if the water is used for drinking purposes.</p><p><strong> (vii)</strong> Aluminium is generally unaffected by air and moisture and it is also good conductor of electricity. That is why it is used in transmission cables.</p>

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