Question

Calculate the molar mass of an element if it forms fee unit cell structure [mass of unit cell =1.8 × 10^-22 g, N_A = 6.022 × 10²³ mol^-1]

Options

• 27.0 g mol^-1

• 24.4 g mol^-1

• 21.0 g mol^-1

• 30.2 g mol^-1

Answer 1

27.0 g mol^-1

Explanation:

In fcc lattice, no. of atoms per unit cell = 4

Mass of unit cell = 1.8 × 10^-22 g

\[\text{Mass of l atom}=\frac{1.8\times10^{-22}\mathrm{g}}{4}\]

= 0.45 × 10^-22 g

Molar mass of the element

= 0.45 × 10^-22 × 6.022 ×10²³ g mol^-1

= 2.709 × 10 g ≈ 27.0 g mol^-1