Question

Compute the difference in masses of 10³ moles each of magnesium atoms and magnesium ions. (Mass of an electron = 9.1×10^-31 kg)

Answer 1

• Magnesium$\left(\mathrm{Mg}\right)$ atom has 12 electrons
• Electronic configuration of $\left(\mathrm{Mg}\right)$ is $1{\mathrm{s}}^2,2{\mathrm{s}}^2,2{\mathrm{p}}^6,3{\mathrm{s}}^2$
• Magnesium ion$\left({\mathrm{Mg}}^{2+}\right)$ has 10 electrons
• Electronic configuration of $\left({\mathrm{Mg}}^{2+}\right)$ is $1{\mathrm{s}}^2,2{\mathrm{s}}^2,2{\mathrm{p}}^6$

$\left({\mathrm{Mg}}^{2+}\right)$ ion and $\left(\mathrm{Mg}\right)$ atom differ by two electrons.

${10}^3$ moles of $\left({\mathrm{Mg}}^{2+}\right)$ and $\left(\mathrm{Mg}\right)$ atoms would differ by $2\times {10}^3$ moles of electrons

Mass of $2\times {10}^3$ moles of electrons

Given:- Mass of an electron- $9.1\times {10}^{-31}\mathrm{Kg}$

= $2\times {10}^3\times 6.023\times {10}^{23}\times 9.1\times {10}^{-31}\mathrm{Kg}$

= $2\times 6.023\times 9.1\times {10}^{-5}\mathrm{Kg}$

= $109.6004\times {10}^{-5}\mathrm{Kg}$

Mass of $2\times {10}^3$ moles of electrons = $1.096\times {10}^{-3}\mathrm{Kg}$.