Derive the formula of the ferric oxide
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.
A 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 =
Stoichiometric ratio of Fe : O = 4:6 = 2:3 Hence, formula of ferric oxide = Fe2O3.