Question

Compound AB has rock salt type structure. The formula weight of AB is 6.023 Y amu and closest AB distance is Y1/3 nm, where Y is any arbitrary number.

(a) Find the density of the lattice

(b) If density of lattice is found out to be 20 Kg / m3 then predict the type of defect

Answer 1

For NaCl, number of formula units per unit cell is 4.

Distance between AB = a / 2 or a = 2Y1/3 x 10-9

Volume of unit cell = a3

Density = 5 Kg / m3

Experimental Density is 20 Kg / m3. Since the density increases so the defect present is metal excess due to interstitial cation.