Rock salt has density $2.16 g c m^{- 3}$ (Na = 23, Cl = 35.5, $N_{A} = 6.02 \times 1 0^{23} mo l^{- 1}$ ). Treat the crystal as built of independent $NaCl$ formula units. The average volume occupied by one $NaCl$ formula unit is $x \times 1 0^{- 23} c m^{3}$ . Find $x$ to one decimal place.

Numerical answer type, tolerance 0.05.

Answer: 4.5

Volume of

1

mol

= 58.5/2.16 = 27.08 c m^{3}

. Per formula unit:

27.08/ (6.02 \times 1 0^{23}) = 4.50 \times 1 0^{- 23} c m^{3}