Question 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.
Class XI The p-Block Elements Page 324
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(i) Al reacts with conc.HNO₃ to form a protective layer of Aluminium oxide on its surface which prevent it from further reaction.
e.g., 2Al + 6HNO₃ --------> Al₂O₃ (alumina ) + 6NO₂ + 3H₂O
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a protective layer
Therefore, Al becomes passive that's why Aluminium containers can be used for the transportation of conc. HNO₃.
(ii) NaOH, sodium hydroxide reacts with Al to evolve dihydrogen gas. the pressure of hydrogen gas can be used to open drains.
the reaction is : 2NaOH + 2Al + 2H₂O ------> 2NaAlO₂ + 3H₂ ↑
(iii) graphite has layered structure. layers are held together by weak Van - der - Waal's forces and hence, can be made to slip over one another. therefore, Graphite acts as dry lubricant.
(iv) in diamond, each sp³-hybridized carbon are linked to four other carbon atoms. it has three dimensional network of carbon atoms . it is very difficult to break extended covalent bonding and therefore diamond is a hardest substance on the earth. that's why it is used as an abrasive.
(v) Aluminium alloy such as duralumin is light,tough and resistant to corrosion and hence, it is used making aircraft body.
e.g., 2Al + 6HNO₃ --------> Al₂O₃ (alumina ) + 6NO₂ + 3H₂O
|
a protective layer
Therefore, Al becomes passive that's why Aluminium containers can be used for the transportation of conc. HNO₃.
(ii) NaOH, sodium hydroxide reacts with Al to evolve dihydrogen gas. the pressure of hydrogen gas can be used to open drains.
the reaction is : 2NaOH + 2Al + 2H₂O ------> 2NaAlO₂ + 3H₂ ↑
(iii) graphite has layered structure. layers are held together by weak Van - der - Waal's forces and hence, can be made to slip over one another. therefore, Graphite acts as dry lubricant.
(iv) in diamond, each sp³-hybridized carbon are linked to four other carbon atoms. it has three dimensional network of carbon atoms . it is very difficult to break extended covalent bonding and therefore diamond is a hardest substance on the earth. that's why it is used as an abrasive.
(v) Aluminium alloy such as duralumin is light,tough and resistant to corrosion and hence, it is used making aircraft body.
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