Class 12th Chemistry 2017 Set1 Delhi Board Paper Solution

Question 25

Calculate the number of unit cells in 8.1 g of aluminium if it crystallises in a f.c.c. structure. (Atomic mass of Al = 27 g mol -1 )

Answer

27 g of Aluminium have 6.02 x 1023 atoms of Al

8.1g of Aluminium have 6.02 x 1023 x 8.1 / 27

= 12.06 x 1022 atoms of Aluminium

Now in FCC structure:

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

12.06 x 1022 atoms have 1/4 x 12.06 x 1022 unit cells

= 3.05x 1022 unit cells