Solid State Question 98
Question: Lithium borohydride crystallizes in an orthorhombic system with 4 molecules per unit cell. The unit cell dimensions are $ a=6.8\overset{o}{\mathop{A}},b=4.4\overset{o}{\mathop{A}} $ and $ c=7.2\overset{o}{\mathop{A.}} $ If the molar mass is 21.76, then the density of crystals is:
Options:
A) $ 0.6708,g,cm^{-2}$
B) $ 1.6708,\text{g}\cdot\text{cm}^{-3}$
C) $ 2.6708,\text{g}\cdot\text{cm}^{-3}$
D) None of these.
Show Answer
Answer:
Correct Answer: A
Solution:
[a] $ d=\frac{ZM}{a^{3}N _{A}}= $
$ \frac{4\times 21.76}{6.8\times {{10}^{-8}}\times 4.4\times {{10}^{-8}}\times 7.2\times {{10}^{-8}}\times 6.023\times 10^{23}} $
$ =0.6708,g,cm^{-2}$
BETA
