Question

At room temperature, polonium Crystallises in a primitive cubic unit cell. If a = 3.36 Å. Calculate the theoretical density of polonium. [It's atomic weight is 209 g/mol.]

Options

• 9.15 g/cm³

• 10.33 g/cm³

• 6.22 g/cm³

• 9.74 g/cm³

Answer 1

9.15 g/cm³ 

Explanation:

Given number of atoms per unit cell, Z = 1

Molecular weight, M = 209 g/mol

Avogadro number, N_A = 6.022 × 10²³

V = a³ = (3.36 × 10^-8)³ cm³   ...[∵ Z = 1]

We know that,

d = `"ZM"/("N"_"A""V")`

`= (1 xx 209)/(6.022 xx 10^23 xx (3.36 xx 10^-8)^3)`

= 9.15 g/cm³