Compute the difference in masses of one mole each of aluminium atoms and one mole of its ions. (Mass of an electron is 9.1 x 10-28 g). Which one is heavier?

Mass of 1 mole of aluminium atom = Molar mass of aluminium = 27 g mol^-1 .

An aluminium atom needs to lose three electrons to become an ion, Al³⁺ .

For one mole of Al³⁺ ion, three moles of electrons are to be lost.

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

= 27.3 x 6.022 x 10^-5g

= 164.400 x 10^-5 g

= 0.00164 g

Molar mass of Al³⁺ = (27- 0.00164) g mol^-1

= 26.9984 g mol^-1

Difference = 27- 26.9984

                  = 0.0016 g