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 ($9.1\times {10}^{-28}g$) . Which one is heavier?

Answer 1

We know that

• Mass of 1 mole of aluminium atom= 27 g / mol
• An aluminium atom needs to lose three electrons to become an ion, ${\mathrm{Al}}^{3+}$
• For one mole of ${\mathrm{Al}}^{3+}$ion, three moles of electrons are to be lost
• The mass of three moles of electrons$$\begin{gathered} =3\times (9.1\times {10}^{-28})\times 6.022\times {10}^{23}g \\ =27.3\times 6.022\times {10}^{-5}g \\ =164.400\times {10}^{-5}g \\ =0.00164g \end{gathered}$$
• Molar mass of ${\mathrm{Al}}^{3+}$$$\begin{gathered} =(27-0.00164)gmo{l}^{-1} \\ =26.9984mo{l}^{-1} \end{gathered}$$

Hence, Difference=(27-26.9984)=0.0016 g