Wustite $Fe X_{0.95} O$ has the rock-salt structure with edge length $430 pm$ (4 formula units per cell). Atomic masses: Fe $= 56$ , O $= 16$ ; $N_{A} = 6.022 \times 1 0^{23} mo l^{- 1}$ . Calculate its density in $g c m^{- 3}$ (two decimals).

Numerical answer type, answer in g cm^-3, tolerance 0.02.

Answer: 5.78 g cm^-3

Mass of one formula unit

= 0.95 \times 56 + 16 = 69.2 g mo l^{- 1}

ρ = \frac{4 \times 69.2}{6.022 \times 1 0 ^{23} \times ( 4.30 \times 1 0 ^{- 8} ) ^{3}} = 5.7812 \approx 5.78 g c m^{- 3}