Ferric oxide crystallises in a hexagonal close-packed array of oxide ions with two out of every three octahedral holes occupied by ferric ions. Derive the formula of the ferric oxide.


Given,

Ferric oxide crystalizes in a hexagonal close packed array of oxide ions.


Two out of every three octahedral holes are occupied by ferric ions.


Let the number of oxide ions = x


Since, two out of every three octahedral holes are fitted by ferric ions.


Thus, voids filled by ferric ions


(Fe3+)


Therefore, number of ferric ions


(Fe3+)


Now, the ratio of ferric ions to the oxide ions


i.e. Fe3+ : O2- =


= Fe3+ : O2- = = 2 : 3


Thus, formula of ferric oxide is Fe2O3 .


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