Question

calculate the number of unit cells in 8.1 gram of aluminium if it crystallizes in a fcc structure.

Answer 1

The weight of one mole of a substance is equal to its atomic mass in grams , therefore

1 mole of Al =27g=27g of Aluminium

Also , 1 mole contains Avogadro number of atoms

1mole=6.023×10²³ atoms of Aluminium

Therefore

1 mole of Al - 27 g of aluminium - 6.023×10²³ atoms of aluminium

Number of atoms in 8.1g8.1g aluminium is =(8.1×6.023×10²³)/27

The face centered cubic structure contains 4 atoms in one unit cell .

Therefore , the number of unit cells.

(8.1×6.023×10²³)/(27×4)=4.516×10²³

Answer 2

Hey !!

n = given mass/molar mass

    = $\frac{8.1}{27} mol$

Number of atoms = 8.1/27 × 6.022 ×× 10²³

Number of atoms in one unit cell = 4 (fcc)

Number of unit cell = [8.1/27 × 6.022 × 10²³]

    FINAL RESULT = 4.5 × 10²²

GOOD LUCK !!