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

Soln:

Mass of one mole of Aluminium atom = {13 × mass of each electron + 13 × mass of each proton + 14 × mass of each neutron} × Avogadro's constant.

We know, if atoms convert into ions, only transfer of electrons takes place, in Al+3 ion, Aluminium atom loss three electrons,

So,

Mass of Al+3 ={10× mass of each electron +13 × mass of each proton + 14 × mass of each neutron} Avogadro's constant

Now,

You see mass of aluminium atom is greater than aluminium ion by 3 electrons Difference in mass =Mass of Aluminium atom -mass of aluminium ion

= 3 × mass of each electron x Avogadro's constant .

= 3 × 9.1 × 10^-28x 6.023 x 10²³

=27.3 x 10^-28 x 6.023 x 10²³ g

=164.4 x 10^-5 g

= 1.644 x 10^-3 g

= 0.0016 g