Question

__________ is used during the isolation of magnesium from seawater.

• A. Reduction with carbon
• B. Electrolytic reduction
• C. Reduction with more reactive metal
• D. None of the above

Answer 1

Answer: (B)

Electrolytic reduction

In sea water, $MgC{l}_2$ is present.

$MgC{l}_2+Ca(OH{)}_2\to Mg(OH{)}_2\downarrow +CaC{l}_2$

$Mg(OH{)}_2\stackrel{Delta}{\to }MgO+H_{2}O$

$MgO+C+C{l}_2\stackrel{Delta}{\to }MgC{l}_2+CO\uparrow$

The anhydrous magnesium chloride is fused with NaCl and anhydrous calcium chloride, The mixture is electrolyzed at 700${}^{\circ }$C in the presence of an inert gas in an electrolytic cell. Magnesium is discharged at the cathode. The purpose of the addition of $NaCl$ and $CaC{l}_2$ to anhydrous $MgC{l}_2$ is to lower the fusion temperature and make the fused mass a good conductor of electricity, Sodium chloride prevents the hydrolysis of magnesium chloride.
At anode: $2C{l}^{-}\to C{l}_2+2e^{-}$
At cathode: $M{g}^{2+}+2e^{-}\to Mg$