An ionic compound AB has a rock salt structure with A :B = 1:1. the formula mass of AB is 6.023 y amu and the closest A-Bdistance isy^(1//3)nm. (a)Calculate the density of the attice. (b) If the observed density of the lattice is found to be20 " kg m"^(-3). then predict the type of defect.

An ionic compound AB has a rock salt structure with A :B = 1:1. the fo

1.	An ionic compound AB has a rock salt structure with A :B = 1:1. the formula mass of AB is 6.023 y amu and the closest A-Bdistance isy^(1//3)nm. (a)Calculate the density of the attice. (b) If the observed density of the lattice is found to be20 " kg m"^(-3). then predict the type of defect.
Answer» Solution :(a) As AB has ROCK salt structure, i.e, has fcc structure , Z =4 Edge of the unit cell =` 2(r_(A+)+ r_(B-)) = 2xx d_(A-B)= 2 x y^(1//3)nm = 2 xx y^( 1//3)xx 10^(-9) ` m Calcualted density `(p)= (Z xxM)/(a^(3)xxN_(0)) = ( 4xx (6.023 y xx10^(-3) " kg mol"^(-1)))/((2y^(1//3) xx10^(-9) m)^(3) (6.023 xx 10^(23)"mol"^(-1)))= 5.0" kg m"^(-3)` (b) As observed density of AB is ` 20 " kg m"^(-3)` which is higher than the calcualted density ` ( 5.0 " kg m"^(-3))` , thisshow that ABhas either interestital impurity defect or substitutional impurity defect.