Question
Sat February 12, 2011 By: Dipti Priya

Ferric oxide crystallizes 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.

Expert Reply
Sun February 13, 2011
Dear Student
 
Unit cell of hcp structure = 6 No. of oxide ions per unit cell = 6 No. of octahedral voids = 6 Since, ferric ions occupy only two out of every three octahedral voids, Therefore, no. of octahedral holes occupied by ferric ions = 2/3 X 6 = 4 Stoichiometric ratio of Fe and O = 4:6 = 2:3 Hence, formula of ferric oxide = Fe2O3.
 
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