Question

An element has a bee structure with cell edge of 288 pm. The density of element is 7.2 g cm^-3. What is the atomic mass of an element?

Options

• 25.89

• 51.78

• 77.68

• 62.43

Answer 1

51.78

Explanation:

Given,

Cell is bcc, so Z = 2

Edge length (a) = 288 pm

= 2.88 × 10^-8 cm

Density of metal (d) = 7.2 g cm^-3

N_A = 6.022 × 10²³

We know that, density (d) = `("Z" xx "M")/("a"^3 * "N"_"A")`

`therefore "M" = ("d" * "a"^3 * "N"_"A")/"Z"`

`= (7.2 xx (2.88 xx 10^-8) xx 6.022 xx 10^23)/2`

`= (7.2 xx 23.8878 xx 10^-24 xx 6.022 xx 10^23)/2`

= 51.78 g mol^-1