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Oxides of Nitrogen

Pure conc. ...

Question

Pure conc. $H {N O}_{3}$ makes iron passive, as the layer of ______ is formed on the surface.

{F e}_{2} O_{3}

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F e O

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{F e}_{3} O_{4}

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F e {({N O}_{3})}_{3}

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Solution

The correct option is A ${F e}_{2} O_{3}$
Conc. nitric acid is a strong oxidizing agent. It oxidizes iron to form a layer of $F e_{2} O_{3}$ . This layer is non-reactive and cannot be oxidized further. Therefore, iron becomes passive to further reaction.

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Similar questions

F e

F e O

{F e}_{2} O_{3}

{F e}_{3} O_{4}

{F e}_{2} O_{3}

{F e}_{3} O_{4}

O_{2}

F e O (s) + {F e}_{2} O_{3} (s) ⟶ {F e}_{3} O_{4} (s)

2 F e (s) + O_{2} (g) ⟶ 2 F e O (s); Δ H^{o} = - 544 k J

4 F e (s) + 3 O_{2} (g) ⟶ 2 {F e}_{2} O_{; 3} (s); Δ H^{o} = - 1648.4 k J

{F e}_{3} O_{4} (s) ⟶ 3 F e (s) + 2 O_{2} (g); Δ H^{o} = + 1118.4 k J

H N O_{3}

H N O_{3}

Δ G = - 177 K c a l

(1) 2 F e (s) + \frac{3}{2} O_{2} (g) ⟶ {F e}_{2} O_{3} (s)

Δ G = - 19 K c a l f o r (2) {4 F e}_{2} O_{3} (s) ⟶ {3 F e}_{3} O_{4} (s)

{F e}_{3} O_{4}

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