Chemistry - Solid State Question with Solution | TestHub

This problem is based on determination of molecular formula of solid which can be determined by using following steps.

Since O-atom form FCC unit cell, the number of

O-atoms per unit cell$=\underset{\text{Face atom}}{6\times \frac{1}{2}+8}\times \underset{\text{Corner atoms}}{\frac{1}{8}=4}$

Number of B atoms at octahedral voids = Number of O-atoms = 4

Number of A atoms at tetrahedral voids

= 2 x Number of O-atoms

= 2 x 4 = 8

Initial formula of compound is A₈ B₄O₄

After removal about two body diagonal

A atom$\Rightarrow 8-4=4$(Removed from 2 body diagonals)

B atoms$\Rightarrow 4-1=3$(Removed from body centre)

O atom$\Rightarrow 4-4\times \frac{1}{8}=3.5$(Removed 4 corners)

Formula will be A₄B₃O_3.5i.e. A₈B₆O₇