Mass of 1 mole of aluminium atom = the molar mass of aluminium = 27 g mol^–1

A aluminium atom and ion, differ by three electrons. Aluminium loses three electrons to form aluminium ion.

The mass of one electron = 9.1×10^–28 g

For one mole of A1³⁺ ion, three moles of electrons are to be lost

Therefore, total number of electrons lost = 3

The mass of three moles of electrons = 3 × (9.1×10^–28) × 6.022×10²³ g

= 27.3 × 6.022 ×10^–5 g

= 164.400 ×10^–5 g

= 0.00164 g

Molar mass of Al³⁺ = molar mass of aluminium – mass of electrons

= 27–0.00164 = 26.9984 g mol^–1

Therefore, difference in masses of one mole each of aluminium atoms and one mole of its ions

= 27 – 26.9984 = 0.0016 g