Question 41
Compute the difference in masses of one mole each of aluminium atoms and one mole of its ions. (Mass of an electron is $9.1\times {10}^{-28}g)$ which one is heavier?

Ionisation of AI atom occurs as $Al\to A{l}^{3+}+3e^u$
Therefore, $A{l}^{3+}$ ion is formed from Al atom by loss of 3 electrons. Difference in mass of 1 mole of Al atoms and 1 mole of $A{l}^{3+}$ ions
$=massof3\times 6.022\times {10}^{23}electrons$
$=(3\times 6.022\times {10}^{23})\times (9.1\times {10}^{-28}g)$
(as mass of an electron $=9.1\times {10}^{-28}g$)
$=164.4\times {10}^{-5}g=1.644\times {10}^{-3}g$
1 mole of Al atoms is heavier than 1 mole of $A{l}^{3+}$ ions.
It is because 1 mole of Al atom have $e^{-}=13\times 6.022\times {10}^{23}$ electrons and 1 mole of Al ion have $e^n=10\times 6.022\times {10}^{23}$ electrons.