Question

Copper crystallises with fee unit cell. If the radius of copper atom is 127.8 pm, calculate the density of copper? (At. mass: Cu = 63.55 g mol^-1)

Options

• 9.5 g cm^-3

• 1.89 g cm^-3

• 4.4 g cm^-3

• 8.9 g cm^-3

Answer 1

8.9 g cm^-3 

Explanation:

`rho = "nM"/("a"^3"N"_"a")`

`"4r"/sqrt2` = a

∴ a = `(4 xx 1.278 xx 10^-8 "cm")/sqrt2`

a = 3.615 × 10^-8 cm

a³ = 47.25 × 10^-24 cm

∴ `rho = (4 xx 63.55)/(47.25 xx 10^-24 xx 6.022 xx 10^23)`

`= 254.2/28.45`

= 8.934 g cm^-3