Question

Calculate no of unit cells in 8.1 g of al if it crystallise in fcc

Answer 1

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

1 mole of Al =27g of Aluminium

Also , 1 mole contains Avogadro number of atoms

1mole=6.023×10^23 1mole=6.023×10^23 atoms of Aluminium

Therefore

1 mole of Al - 27 g of aluminium - 6.023×10^23 atoms of aluminium

Number of atoms in 8.1g aluminium is =(8.1×6.023×10^23)/27

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

Therefore , the number of unit cells that has (8.1×6.023×1023)/27 atoms of Aluminium can be obtained as ,

(8.1×6.023×1023)/(27×4)=4.516×1022