Aluminium is stable in air and water in spite of the fact that it is reactive metal. The…
Chemistry · JEE Advanced · NTA Exams — p-Block Elements
Aluminium is stable in air and water in spite of the fact that it is reactive metal. The reason is that a thin film of its oxide is formed on its surface which it passive for further attack. The layer is so useful that in industry, it is purposely deposited by an electrolytic process called anodising
Reaction of aluminium with oxygen is highly exothermic and is called thermite reaction.
\(\text { ÄAIl(v) } \mathrm{H}_{2}^{3} \mathrm{O}_{2} \mathrm{O}(\mathrm{~g}) \rightarrow \mathrm{Al}_{2} \mathrm{O}_{3}(\mathrm{~s}) \text {; }\)
Thermite reaction finds applications in the metallurgical extraction of many metals from their oxides and for welding of metals. The drawback is that to start the reaction, high temperature is required for which an ignition mixture is used.
Anodising can be done by electrolysing dilute H2SO4 with aluminium as anode. This results in :
- the formation of Al2(SO4)3 on the surface of aluminium anode
- the formation of oxide film (Al2O3) on the surface of aluminium anode
- the formation of polymeric aluminium hydride film on the surface of aluminium anode
- none of the above
Answer
(B) the formation of oxide film (Al 2 O 3 ) on the surface of aluminium anode
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