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(a) Indicate the temperature at which ca...

(a) Indicate the temperature at which carbon can be used as reducing agent for `FeO`.
(b) Define flux.
( c) Metal usually do not occur in nature as nitrates. Why ?
(d) Metal such as `Cu, Ag, Zn` etc. occur in nature as sulphide rather than oxides. Why ?

Text Solution

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(a) At `1073 K` or above, the standard free energy of formation of `CO` from `C` is much below the standard free energy of formation of `FeO`. Hence, above `1073 K`, carbon can reduce `FeO` to `Fe`.
(b) Flux is a substance that combines with gauge, which mat still be present in the roasted or calcinaed ore to form an easily fusible material called slag.
( c) Nitrates of all metals are soluble in water. Hence, if metal nitrates are present in the crust of earth, these would be slowly and gradually washed by rain water into the sea. Hence, metals usually do not occur in nature as nitrates.
(d) The cations of `Cu, Ag` and `Zn`, i.e. `Cu^(oplus), Ag^(oplus)` and `Zn^(2+)` [pseudo inert gas configuration, `(ns^(2) p^(6) d^(10))`] have high polarising power and hence easily polarises the bigger sulphide `(S^(2-))` ion than the small oxide `(O^(2-))` ion. Hence, sulphides of these metals are more stable than the oxides and these metals occur in nature as sulphides rather than oxides.
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