11th Class Chemistry The p-Block Elements-I

  • question_answer 30) Give reasons: (i) Conc. \[HN{{O}_{3}}\]can be transported in aluminium containers. (ii) Graphite is used as a lubricant. (iii) Diamond is used as an abrasive. (iv) A mixture of \[NaOH\]and aluminium pieces is used to open the drain. (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.  

    Answer:

    (i) Al becomes passive in cone. \[HN{{O}_{3}}\]. A thin film of oxide is formed on its surface which prevents further action of\[HN{{O}_{3}}\]. Hence, containers of passive aluminium can be safely used for transporting conc. \[HN{{O}_{3}}\]. (ii) Graphite has a layered structure in which various layers are held by van der Waals' forces. These layers can be made to slip over one another. Therefore, graphite acts as a lubricant. (iii) On account of hardness of diamond, it is used as an abrasive. (iv) \[NaOH\]reacts with Al and produces hydrogen. The pressure of the released hydrogen can be used to open the clogged drains. (v) Al alloys are light and corrosion resistant. These are tough and hence are used to make aircraft body. (vi) Aluminium is slowly attacked by water and dissolves oxygen to form \[A{{l}_{2}}{{O}_{3}}\] on the surface. A very very small amount of\[A{{l}_{2}}{{O}_{3}}\]may dissolve to give a few \[A{{l}^{3+}}\] ions. Since, \[A{{l}^{3+}}\] ions are injurious to health, the drinking water should not be kept in aluminium vessels for long. (vii) Al is a good conductor of electricity and is also not affected by atmosphere. Hence, it is used in transmission cables.  


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