If FeO crystallizes according to rock salt structure, where O 2 − is equivalent to Cl − ion. Due to some crystal defect, lattice becomes Fe 0.75 O . Find no. of effective Fe 2 + ions per unit cell -

Question

If FeO crystallizes according to rock salt structure, where O 2 − is equivalent to Cl − ion. Due to some crystal defect, lattice becomes Fe 0.75 ​ O . Find no. of effective Fe 2 + ions per unit cell -

TestHub · Accepted Answer

In FeO (rock salt structure), O²⁻ ions form an FCC lattice, so the number of O²⁻ ions per unit cell is $4$ .

Given the formula is Fe₀.₇₅O, the number of Fe ions per unit cell is:

$4 \times 0.75 = 3$

Due to Fe deficiency, some Fe²⁺ ions are converted into Fe³⁺ ions. The charge balance is:

$3 (2 +) = 6$ , oxygen charge $= 4 (2 -) = 8$

The extra positive charge required is $2$ , so two Fe²⁺ ions become Fe³⁺. The effective number of Fe²⁺ ions is:

$3 - 2 = 1$

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