In the electrolysis of of a aqueous solution, if the cathode used is exclusively a liquid Mercury () — Electrochemistry Chemistry Question

💡 Solution & Explanation

The $500\text{ mL}$ of $4.0\text{ M}$ $NaCl$ contains $2.0$ moles of $Na^+$. At a mercury cathode, sodium is preferentially discharged due to the high overvoltage of hydrogen on mercury, forming an amalgam: $Na^+ + e^- + Hg \rightarrow NaHg$. Since 2.0 moles of $Na^+$ reduce to form 2.0 moles of $NaHg$, the total mass is $2.0 \times (23 + 200) = 2.0 \times 223 = 446\text{ g}$.