Calculate the number of molecules in one kg of calcium chloride.

Mass of 1 mole of CaCl₂ = Ca + 2Cl = 40 + (2 x 35.5) = 40 + 71 = 111 g

111 g of CaCl₂ contains 6.022 × 10²³ molecules

∴ 1000 g of CaCl₂ contains $\dfrac{6.022 \times 10^{23} \times 1000}{111}$

= 5.42 × 10²⁴ molecules