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?

Answer 1

Given: For the given system,

Z = 4,

a = 0.564 nm = 564 × 10⁻⁷ cm

M = 23 + 35.5 = 58.5,

N_A = 6.022 × 10²³

Formula: `rho = (Z xx M)/(a^3 xx N_A)`

`rho = (4 xx 58.5)/((0.564 xx 10^-7)^3 xx 6.02 xx 10^23)`

`rho = (234)/((0.179 xx 10^-21) xx 6.022 xx 10^23)`

`rho = (234)/(1.077 xx 10^2)`

ρ = 217.2 × 10²

ρ = 2.172 g cm⁻³