Question

A solid cube of aluminum (density 2.7 g/cm3) has a volume
of 0.20 cm^3. How many aluminum atoms are contained in the
cube?

Answer 1

find the mass first
since
density=mass/volume
mass = 2.7 x 0.20 = 0.54 g

then find the no. of moles
no. of moles = mass/molar mass = 0.54/26.98 = 0.020 moles

now multiply it by Avogadro's constant
no. of molecules = no.of moles x Avogadro's constant
= 0.020 x 6.023 x 10^23 = 1.2046 x 10^22 molecules