question_answer 43)

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.

Answer:

There is one octahedral hole for each atom in hexagonal close packed arrangement. If the number of oxide ions (O2-) per unit cell = 1 Then, no. of Fe3+ ions   Thus, the formula of the compound = Fe2/3 O1 = Fe2O3