A unit cell of sodium chloride has four formula units. The edge length of the unit cell is 0.564 nm.

Question

A unit cell of sodium chloride has four formula units. The edge length of the unit cell is 0.564 nm. What is the density of sodium chloride in g/$cm^3$? (Atomic masses: Na = 23, Cl = 35.5)

Professor PC Thomas Classes · Answer

$d = \frac{Z 	imes M}{N_A 	imes a^3} = \frac{4 	imes 58.5}{6.023 	imes 10^{23} 	imes (0.564 	imes 10^{-7})^3} = \frac{234}{6.023 	imes 10^{23} 	imes 0.179 	imes 10^{-21}} = \frac{234}{108} \approx 2.16~g/cm^3$.