Question

What is the density of potassium, if it has a bcc structure with edge length 4Å?
(Atomic mass of K = 39)

Options

• 3 g cm^-3

• 2 g cm^-3

• 5 g cm^-3

• 4 g cm^-3

Answer 1

2 g cm^-3 

Explanation:

For density, `rho = ("Z" xx "M")/("a"^3 xx "N"_"A")`

Edge length, a = `4Å = 4 xx 10^-8` cm

For bcc structure, Z = 2

`rho = (2 xx 39)/((4 xx 10^-8)^3 xx 6.022 xx 10^23)`

`= 0.202 xx 10^24 xx 10^-23 " g cm"^-3`

= 0.202 × 10 g cm^-3 

= 2.02 g cm^-3