Question

The density of $Ca{F}_2$ (fluorite structure) is $3.18$ g cm${}^{-3}$. The length of the side of the unit cell (in pm) is:

• A. $253$
• B. $344$
• C. $546$
• D. $273$

Answer 1

The correct option is C $546$

$d=\frac{zM}{N_A\times V}$

For flourite structure, $z=4$ and $M=78$

$3.18=\frac{4\times 78}{6.023\times {10}^{23}\times a^3}$

$a^3=\frac{312}{6.023\times {10}^{23}\times 3.18}$

$a^3=16.28\times {10}^{-23}$

$a=546$ pm