Question

Aluminium crystallizes in FCC. Calculate number of unit cell in 0.8 g aluminium (at wt. of Al=27)

Answer 1

27 g of Aluminium have $6.02\times {10}^{23}$ atoms of Al

0.8 g of Aluminium have $6.02\times {10}^{23}\times 0.8\times \frac{1}{27}$

$=1.78\times {10}^{22}$ atoms of Aluminium

Now in FCC structure:

1 unit cell has 4 Aluminium atoms i.e.,

$1.78\times {10}^{22}$ atoms have $\frac{1}{4}\times 1.78\times {10}^{22}$ unit cells

$=4.45\times {10}^{21}$ unit cells