Question

Ice crystallises in a hexagonal lattice having the volume of unit cell as 132 × 10–24 cm3. if density is 0.92 g cm–3 at a given temperature then number of h2o molecules per unit cell is

Answer 1

Mass =  Volume x Density

Mass = 132 × 10–24 x 0.92 

          = 1.2144 x 10^-22 g

1 mole of H2O has a mass of 18g

Avogadros number = 6.022 X 10^23


Number of moles of H2O =  (1.2144 x 10^-22)/ 18

                                         =  6.747 x 10^-24


Avogadros number = 6.022 X 10^23

Number of H2O molecules = 6.022 X 10^23 x 6.747 x 10^-24

                                            = 4

Answer 2

Hey !!

ρ = Z × M / a³ × N₀. The aim is to find Z

       0.92 =  Z × 18 / (132 × 10⁻²⁴) (6.02 × 10²³)

          = Z × 18 / 132 × 6.02 × 10⁻¹

(OR)         Z = 0.92 × 132 × 6.02 × 10⁻¹ / 18

FINAL RESULT = 4.06

Hope it helps you !!