Step 1: Calculate the molar mass of aluminum chloride.
Molar mass of aluminum chloride = 27.0 + 35.5 = 62.5 g/mol
Step 2: Calculate the number of moles.
Number of moles = (5.73 x 10^20 formula units) x (1 mol/6.02 x 10^23 formula units)
Number of moles = 9.5 x 10^-4 moles.