Question

Lithium has a bcc structure .Its density is `530 kg m^(-3)` and its atomic mass is `6.94 g mol^(-1)` .Calculate the edge length of a unit cell of lithium metal `(N_(A) = 6.02 xx 10^(23) mol^(-1))`
A. `264p m`
B. `154p m`
C. `352p m`
D. `527p m`

Answer 1

Correct Answer - 3
According to the density formula we have
`d=(ZM)/(a^(3)N_(A))`
or `a^(3)=(ZM)/(dN_(A))=((2"atoms")(6.94g mol^(-)))/((0.530g cm^(-3))(6.02xx10^(23)"atoms" "mol"^(-1)))`
`= 4.350xx10^(-23)cm^(3)`
thus `a=(4.350xx10^(-23)cm^(3))^(1//3)`
`=3.52xx10^(-8)cm`
`=352p m`