Question

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

Which one is heavier?

Answer 1

• Aluminium$\left(\mathrm{Al}\right)$ has 13 electrons
• $\mathrm{Al}\to {\mathrm{Al}}^{3+}+3{\mathrm{e}}^{-}$
• Aluminium$\left({\mathrm{Al}}^{3+}\right)$ has 10 electrons

Mass of three moles of electrons = (3 × 9.1×10^-28) × 6.023 x 10²³

Mass of three moles of electrons = 0.001644 g

Molar mass of Al³⁺ = 27 – 0.001644

Molar mass of Al³⁺ = 26.99 gmol^-1

Difference in mass = 27 – 26.9984

Difference in mass = 0.0016 g

1 mole of Al atoms is heavier than 1 mole of Al³⁺ions.