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

A Mg²⁺ ion and Mg atom differ by two electrons. 

103 moles of Mg²⁺ and Mg atoms would differ by 

10³ × 2 moles of electrons 

Mass of 2 ×10³ moles of electrons = 2×10³ × 6.023 ×10²³ × 9.1 ×10^–31 kg 

⇒ 2×6.022 × 9.1×10^–5kg 

⇒ 109.6004 ×10^–5 kg 

⇒ 1.096 × 10^–3kg