Question

72. Explain why
(i) Aluminium cannot be extracted by reducing alumina with carbon
(ii)Concentrated HNO, can be stored in aluminum containers.
(iii) Aluminium is used for making transmission wires.
(iii) 24 carat gold cannot be used for making ornaments.
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Answer 1

Answer:

1. Aluminum is too high in the electrochemical series (reactivity series) i.e. it is a stronger reducing agent than carbon and therefore it cannot be extracted from its ore using carbon
2. Concentrated HNO3 can be stored and transported in aluminium containers as it reacts with aluminium to form a thin protective oxide layer on the aluminium surface. This oxide layer renders aluminium passive. (ii) Sodium hydroxide and aluminium react to form sodium tetrahydroxoaluminate(III) and hydrogen gas.
3. Aluminium wire is used to make transmission cables. Aluminium is cheply available on a weight-to weight basis,the electrical conductivity of aluminium is twice that of copper. Hence, aluminium wire is used to make transmission cables.
4. 24 carat gold, or pure gold is very soft and hence cannot be used for making jewellery. So, some amount of other metal, (usually copper and silver) is added in order to make gold a bit harder and give it a shape.

Explanation:

Answer 2

Answer:

Explanation:

Aluminum is too high in the electrochemical series (reactivity series) i.e. it is a stronger reducing agent than carbon and therefore it cannot be extracted from its ore using carbon
Concentrated HNO3 can be stored and transported in aluminium containers as it reacts with aluminium to form a thin protective oxide layer on the aluminium surface. This oxide layer renders aluminium passive. (ii) Sodium hydroxide and aluminium react to form sodium tetrahydroxoaluminate(III) and hydrogen gas.
Aluminium wire is used to make transmission cables. Aluminium is cheply available on a weight-to weight basis,the electrical conductivity of aluminium is twice that of copper. Hence, aluminium wire is used to make transmission cables.
24 carat gold, or pure gold is very soft and hence cannot be used for making jewellery. So, some amount of other metal, (usually copper and silver) is added in order to make gold a bit harder and give it a shape.