Question

 An element crystallises in bcc lattic with a cell edge of 3 × 10^-8cm. The density of the element is 6.89 g cm^-3 . calculate the molar mass of element. (N_A = 6.022 × 10²³ mol^-1)

Answer 1

BCC lattic, Z=2
a = 3 × 10^-8 cm, d = 6.89 gcm^-5 

${\displaystyle d=\frac{Zm}{a^3}}$            m=mass of one atom

${\displaystyle m=\frac{6.89\times {(3\times {10}^{-8})}^3}{2}}$

${\displaystyle m=\frac{6.89\times 27\times {10}^{-24}}{2}}$
molar mas = N_A × m