Question

A compound MpXq has ccp arrangment of X.Its unit cell structure is shown.......Find emperical formula?

(IIT-JEE 2012)

Answer 1

X^- ions are present at the corners and face centers:

Number of x^- ions per lattice = 1/8(Number of ions present at corners of cube) + ½(Number of ions present at face centers) = 1/8(8) + ½(6) = 4

M⁺ ions are present at the four edge centers and at body center. corners and on face centers:

Number of M⁺ ions per lattice = 1/4(Number of ions present at edge centers of cube) + (Number of ions present at body center) = 1/4(4) + 1 = 2

Now: X: M = 4:2 = 2:1

So, the formula should be MX₂