Question

How many unit cells are present in 39 g of potassium?

Answer 1

First of all, we know that

• The atomic weight of potassium is 39.
• There are 8 atoms on the corners of cube of which 1/8th part is inside the cube.
• One atom is present at the center of the cube.

so, the number of atom in one cube -

=> 1/8×8+1×1

=> 1+1

=> 2

now no. of atoms in 39gm of potassium,

=> 39/39×6.023×10^23

=>6.023×10^23

now,

number of unit cell in 39gm of potassium

=>(6.023×10^23) / 2

=>3.011×10^23.

Answer 2

Answer:

Atomic mass of potassium is 39 g.

In a BCC unit cell, there are 8 atoms at the corner of a cube and 1 atom at the centre.

Number of atom per unit cell =  

8 x 1/8 + 1 x 1 = 2  

Number of atoms in 4.0 g of potassium = 4/39 x 6.02 x 10^23  

Number of unit cells in 4.0 g of potassium = 4/39 x 6.02 x 10^23/2  = 3.09 x 10^22 unit cells

Explanation: