A metal has a fcc lattice. The edge length of the cell is 404 pm. The density of the metal is 2.72 g cm−3 . The molar mass of the metal is
(NA Avogadro's constant = 6.02×1023mol−1)
27 g mol−1
For fcc, Z=4
Note: We will convert all units to cm from m, this is an important step as density is given in g/cc. This will take care of the units of molar weight as well - g/mol.
d=ZMNAa3⇒M=d×NA×a3Z=2.72×6.023×1023×(404×10−10)34M=26.99≃27 g mol−1