What will be 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).

Difference in masses of one mole each of aluminium atoms and one mole of its ions is 0.0016 g.

The difference in Al atom and Al³⁺ ion is of 3 electrons because an Al atom loses 3 electrons to become Al³⁺ ion.

$\mathrm{Mass} \mathrm{of} 1 \mathrm{mole} \mathrm{of} \mathrm{Al} \mathrm{atoms} =\mathrm{ }27 \mathrm{g}$
For one mole of Al³⁺, 3 moles of electrons are to be lost.
$\mathrm{The} \mathrm{mass} \mathrm{of} 3 \mathrm{mole} \mathrm{of} \mathrm{electrons} =\mathrm{ }3\mathrm{ }\times \mathrm{ }9.1\mathrm{ }\times \mathrm{ }{10\mathrm{ }}^{-28}\times \mathrm{ }6.022\mathrm{ }\times \mathrm{ }{10}^{23}$
                                                        $\mathit{ }\Rightarrow 1.64 \times {10 }^{-3}\mathit{ g\; or }0.00164\mathit{ g}$
$\mathrm{Molar} \mathrm{mass} \mathrm{of} {\mathrm{Al}}^{3+}\mathrm{ }=\mathrm{ }27\mathrm{ – }0.00164$
                                      $\Rightarrow 26.9984\mathit{ g}$
Hence, the difference in mass $= 27\mathit{ – }26.9984$
                                                     $\Rightarrow \mathrm{ }0.0016 \mathrm{g}$