Question

Question 36
Compute the difference in masses of ${10}^3$ moles each of magnesium atoms and magnesium ions.
(Mass of an electron $=9.1\times {10}^{-31}kg)$

Answer 1

${10}^3$ moles of Mg atoms $={10}^3\times 6.022\times {10}^{23}$
$=6.022\times {10}^{26}Mgatoms$
${10}^3$ moles of $M{g}^{2+}$ atoms $={10}^3\times 6.022\times {10}^{23}$
$=6.022\times {10}^{26}M{g}^{2+}ions$
One $M{g}^{2+}$ Ion is formed from one Mg atom by loss of 2 electrons, As $Mg\to M{g}^{2+}+2e^{-}$
i.e., difference in the mass of 1 Mg atom and $1M{g}^{2+}$ ion = mass of 2 electrons
$\therefore$ Difference in the mass of $6.022\times {10}^{26}$ Mg atoms and $M{g}^{2+}$ ions
$=massof2\times 6.022\times {10}^{26}$ electrons
$=2\times 6.022\times {10}^{26}\times 9.1\times {10}^{-31}kg$.
(as mass of an electron $=9.1\times {10}^{-31}kg$).
$=109.6004\times {10}^{-5}kg=1.096\times {10}^{-3}kg=1.096g$