Question

1. Zinc or aluminium do not corrode because :
(A) They do not react with moist air
(B) They react with moist air to form a very thin layer of oxides which is very sticky and hard
(C) They are inactive metals
(D) They are metalloids.
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Answer 1

AnswEr :

[B] They react with moist air to form a very thin layer of oxides which is very sticky and hard .

ExplanaTion :

• Case 1 (Reaction of aluminum)

Aluminium doesn't react with air , but if the oxide layer is damaged, the aluminium metal is exposed to attack the air (reaction occurs)

Aluminium will burn in oxygen with a white flame to form the trioxide alumnium(III) oxide, i.e.,

$\large\boldsymbol\purple {4Al_{(s)} + 3O_{2(l)} \longrightarrow 2Al_2O_{3(s)}}$

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• Case 2 (Reaction of Zinc)

Zinc reacts with oxygen in the moist air.

As, Zinc tarnishes in the moist air.

Zinc metal burns in air to form the white zinc(II) oxide, a material that turns yellow on continuously or prolonged heating.

$\large \boldsymbol\purple{2Zn_{(s)} + O2_{(g)} \longrightarrow 2ZnO_{(s)}}$

Therefore,

Aluminium and zinc react with moist air to form a thin protective layer of oxide on their surfaces. This Iayer prevents corrosion or rusting of the metals.

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Answer 2

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[B] They react with moist air to form a very thin layer of oxides which is very sticky and hard .