1.

Ferric oxide crystallized 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»

Given: Oxide (O2-) ions form hcp lattice and ferric (Fe3+) ions occupy 2/3rd of the octahedral voids.

To find: Formula of the compound.

Calculation: Let the number of oxide ions (O2- ) in hcp unit cell = n

 \(\therefore\) Number of octahedral voids = n

As\(\cfrac{2}{3}\) rd of the octahedral voids are occupied by ferric ions, the number of ferric ions present

=n\(\times\frac{2}{3}=\frac{2n}{3}\)

\(\therefore\) Ratio of Fe3+ : O2- =\(\frac{2n}{3}:n=2:3\)

Ans: The formula of ferric oxide is Fe2O3.



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