Question

How many unit cells are present in a cube-shaped ideal crystal of NaCl of mass 1.00 g
[Atomic masses: Na=23, Cl=35.5]

• A. 2.57 x 10²¹ unit cells
• B. 5.14 x 10²¹ unit cells
• C. 1.28 x 10²¹ unit cells
• D. 1.71 x 10²¹ unit cells

Answer 1

The correct option is A 2.57 x 10²¹ unit cells

$\frac{1}{58.5}\times 6.023\times {10}^{23}=1.029\times {10}^{22}$
A unit cell contains 4 $N{a}^{+}$ ion and 4 $C{l}^{-}$ ions
$\therefore$ Unit cell $=\frac{1.029\times {10}^{22}}{4}=2.57\times {10}^{21}$ unit cell