Chemistry - Solid State Question with Solution | TestHub

Given:

O²⁻ ions have ccp arrangement.

Fe²⁺ occupies 1/8ᵗʰ of tetrahedral voids.

Fe³⁺ occupies half of the octahedral voids.

Need to find the formula of spinel.

Step 1: Number of oxide ions in ccp unit cell

In ccp (FCC):

O²⁻ = 4 ions per unit cell

Step 2: Number of tetrahedral voids

For $n$ atoms in ccp:

Tetrahedral voids = $2n$

$=2(4)=8$

Fe²⁺ occupies $\frac{1}{8}$ of tetrahedral voids:

Fe²⁺ $=\frac{1}{8}\times 8=1$

Step 3: Number of octahedral voids

For ccp:

Octahedral voids = $n$

$=4$

Fe³⁺ occupies half of octahedral voids:

Fe³⁺ $=\frac{1}{2}\times 4=2$

Step 4: Write formula

Number of ions:

Fe²⁺ = 1

Fe³⁺ = 2

O²⁻ = 4

Formula:

Fe²⁺Fe³⁺₂O₄

or

Fe₃O₄

Correct option:

(B) Fe₃O₄