Question

An element crystallizes bcc type of unit cell, the density and edge length of unit cell is 4 g cm⁻³ and 500 pm respectively. What is the atomic mass of an element?

Options

• 100.1

• 150.0

• 125.5

• 250.0

Answer 1

150.0

Explanation:

In bcc, n = 2, ρ = 4 g cm⁻³

a = 500 pm = 500 × 10⁻¹⁰ cm = 5 × 10⁻⁸ cm

∴ Volume of unit cell, a³ = (5 × 10⁻⁸ cm)³ = 125 × 10⁻²⁴ cm³

Now, M = `(ρ xx "a"^3 xx "N"_"A")/"n"`

= `(4 xx 125 xx 10^-24 xx 6.022 xx 10^23)/2`

= 150.5 g mol⁻¹