Question

The edge length of the unit cell of $NaCl$ crystal lattice is 5.623 ?, density is 2.16 $g cm^{-3}$ and the molar mass of $NaCl$ is $58.5\, g$ $mol^{-1}$. The number of moles per unit cell is

• A. 4
• B. 3
• C. 1
• D. 2

Answer 1

Answer: (A)

4

Answer 2

$Z = \frac{\rho a^{3}N_{A}}{M}$ $= \frac{2.16\times \left(5.623\times 10^{-8}\right)^{3}\times 6.02 \times 10^{23}}{58.5}$ $= 3.95\approx4$