Question

A substance has density of 2 kg dm-3& it crystallizes to fcc lattice with edge length equal to 700 pm, then the molar mass of the substance is

• A. 75.50 gm mol-1
• B. 103.30 gm mol-1
• C. 56.02 gm mol-1
• D. 65.36 gm mol-1

Answer 1

Answer: (B)

103.30 gm mol-1

Answer 2

$\rho = \frac{n \times M_{m}}{N_{A} \times a^{3}}$

$2 = \frac{4 \times M_{m}}{6.023 \times 10^{23} \times (7 \times 10^{- 8})^{3}}$

(Since, effective number of atoms is unit cell = 4 ) on solving we get Mm = 103. 03 gm/mol