Question

Lithium metal has a body centred cubic structure. Its density is $0.53gc{m}^{-3}$ and its molar mass is $6.94gmo{l}^{-1}$. Calculate the edge of a unit cell of Lithium metal.

• A. $153.6pm$
• B. $351.6pm$
• C. $527.4pm$
• D. $263.7pm$

Answer 1

Answer: (B)

$351.6pm$

Given, $z=2,d=0.53gc{m}^{-3}$ Molar mass $m=6.94$

$\Rightarrow a^3=\frac{ZM}{d{N}_A}\Rightarrow a^3=\frac{2\times 6.94}{0.53\times 6.022\times {10}^{23}}$

$\Rightarrow a^3=4.38\times {10}^{-23}$

$\Rightarrow a=0.3516\times {10}^{-7}cm\simeq 351.6pm$

Hence, edge of unit cell is $351.6pm$.