The density of KBr is ` 2.75 " g cm^(-3)` , The length of edge of the unit cell is 654 pm. Predict, the type of cubic lattice to which unit cell of KBr belongs ` ( N_(0) = 6.023 xx 10^(23) " mol" ^(-1) ` , At mass : K = 29 , Br = 80)

Explanation

For cubic crystals ` p = ( Z xx M)/( a^(3) xxN_(0))`
` or Z = ( p xx a^(3) xx N_(0))/ M = (( 2.75 "g cm" ^(-3)) ( 654xx 10^(-10) "cm")^(3) xx ( 6.023 xx 10^(23) "mol"^(-1)))/ (( 39+ 80) "g mol" ^(-1)) = 3.89=4`
Thus, there are four formula units of KBr, present per unit cell. Hence, it has face- centred cubic lattic.