Question

The well-known mineral fluorite is chemically calcium fluoride. In one unit of this mineral, there are 4Ca²⁺ and 8F^- ions arranged in fcc lattice. The F^- ions fill all the tetrahedral void in the fcc lattice. The edge of the unit cell is 5.46 x 10^-8 cm. The density of the solid is 3.18 g/cm³ . Calculate Avogadroís number. (Molar mass of CaF₂ = 78.08 g/mol) 

Answer 1

The edge of the unit cell (a) = 5.46x10^–8 cm

The density of the solid (d) = 3.18 g cm^–3

Molar mass of CaF₂ (M)= 78.08 g mol^–1

We know that density,