An ionic compund 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-B distance is y^(1//3)nm (a)Calculate the density of the lattice. (b)If the observed density of the lattice is found to be 20 kg m^(-3) , then predict the type of defect.

An ionic compund AB has a rock salt structure with A:B=1:1 . The formu

1.	An ionic compund 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-B distance is y^(1//3)nm (a)Calculate the density of the lattice. (b)If the observed density of the lattice is found to be 20 kg m^(-3) , then predict the type of defect.
Answer» Solution :(a)As AB has rock salt structure, i.e., it has fcc structure , Z=4 EDGE of the unit cell = `2(r_(A^+)+r_(B^-))=2xxd_(A-B)=2xxy^(1//3) nm =2xxy^(1//3) xx10^(-9)`m Calculated density `(rho)=(ZxxM)/(a^3xxN_0) =(4xx(6.023 y XX 10^(-3) "kg mol"^(-1)))/((2y^(1//3)xx10^(-9) m)^3 (6.023xx10^23 "mol"^(-1)))=5.0 kg m^(-3)` (b)As observed density of AB is `20 "kg m"^(-3)` which is higher than the calculated density `(5.0 "kg m"^(-3))` , this shows that AB has either interstitial impurity defect or substitutional impurity defect.