Compute the difference in masses of ${10}^3$ moles each of magnesium atoms and magnesium ions.

• (Mass of an electron= 9-1 x ${10}^{-31}$)

• A magnesium ion ${\mathrm{Mg}}^{2+}$and magnesium $\mathrm{Mg}$ atom differ by two electrons.
• So, ${10}^3$moles of ${\mathrm{Mg}}^{2+}$and $\mathrm{Mg}$ atoms would differ by ${10}^3$$\times 2$moles of electrons.
• Mass of $2\times {10}^3$moles of electrons.

$$\begin{gathered} =2\times {10}^3\times 6.022\times {10}^{23}\times 9.1\times {10}^{-31}kg \\ =2\times 6.022\times 9.1\times {10}^{-5} \\ =109.6004\times {10}^{-5} \\ =1.096\times {10}^{-3} \end{gathered}$$