Question

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)

• A. $1.096\times {10}^{-3}$ kg
• B. $0.5486\times {10}^{-3}$ kg
• C. $1.096\times {10}^3$ kg
• D. $0.5486\times {10}^3$ kg

Answer 1

The correct option is A $1.096\times {10}^{-3}$ kg

$Mg\to M{g}^{+2}+2e^{-}$

A $M{g}^{2+}$ ion and Mg atom differ by two electrons.
${10}^3$ moles of $M{g}^{2+}$ and Mg atoms would differ by ${10}^3\times 2$ moles of electrons
Mass of $2\times {10}^3$ moles of electrons $=2\times {10}^3\times 6.023\times {10}^{23}\times 9.1\times {10}^{-31}kg$
$=2\times 6.022\times 9.1\times {10}^{-5}kg$
$=109.6004\times {10}^{-5}kg$
$=1.096\times {10}^{-3}kg$