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Rusting is an electrochemical process. J...

Rusting is an electrochemical process. Justify. If two iron articles are coated with tin and zinc respectively, in which case will the rusting of iron be more rapid, if the coating is worn out in one place. Give a reason.

Text Solution

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Iron when exposed to humid atmosphere gets converted to `Fe^(2+)` due to the formation of `Fe (OH)_(2)` and this is in presence of air `(O_(2))` to form rust. `Fe_(2)O_(3). XH_(2)O`
When tin coating on iron is broken iron gets exposed to atmosphere. Since iron has greater oxidation potential than tin, iron acts as anode and tin acts as cathode. Iron gets oxidised to `Fe^(+2)` ions in preference to tin. Consequently rusting becomes rapid when tin coating on iron is broken. Since Zn has greater oxidation potential than Fe, though Zinc is worn out, Zn present on the rest of the article gets oxidised in preference to Fe. Hence, rusting of Fe is slow.
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Knowledge Check

  • Zinc is coated over ion iron to prevent rusting of iron because :

    A
    it is cheaper than iron
    B
    `E_((Zn^(2+)//Zn))^(@) = E_((Fe^(2+)//Fe))^(@)`
    C
    `E_((Zn^(2+)//Zn))^(@) lt E_((Fe^(2+)//Fe))^(@)`
    D
    `E_((Zn^(2+)//Zn))^(@) gt E_((Fe^(2+)//Fe))^(@)`

  • E^(0) values of three metals are listed below . Zn_((aq))^(2+)+2e^(-) to Zn_((s)), E^(0) = -0.76 V Fe_((aq))^(2+)+2e^(-) to 2Fe_((s)) , E^(0) = -0.44 V Sn_((aq))^(2+) +2e^(-) to Sn_((s)) , E^(0) = -0.14 V Which of the following statements are correct on the basis of the above information ? (i) Zinc will be corroded in preference to iron if zinc coating is broken on the surface. (ii) If iron is coated with tin and the coating is broken on the surface then iron will be corroded. (iii) Zinc is more reactive than iron but tin is less reactive than iron.

    A
    (i) and (ii)
    B
    (ii) and (iii)
    C
    (i),(ii), and (iii)
    D
    (i) and (iii)

  • E^@ values of three metals are listed below. {:(Zn_((aq))^(2+) + 2e^(-) to Zn_((s)),, E^@=-0.76V),(Fe_((aq))^(2+) + 2e^(-) to 2Fe(s) , , E^@=-0.44 V),(Sn_((aq))^(2+)+2e^(-) to Sn_((s)) ,, E^@=-0.14 V) :} Which of the following statements are correct on the basis of the above information ? (i)Zinc will be corroded in preference to iron if zinc coating is broken on the surface. (ii)If iron is coated with tin and the coating is broken on the surface then iron will be corroded . (iii)Zinc is more reactive than iron but tin is less reactive then iron.

    A
    (i) and (ii) only
    B
    (ii)and (iii) only
    C
    (i),(ii) and (iii)
    D
    (i) and (iii) only

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