Question

Explain giving one example, how highly reactive metals (which are high up in the reactivity series) are extracted.

Answer 1

Sodium, potassium, calcium, magnesium and aluminium are highly reactive metals and are placed at the top of the reactivity series. These metals are extracted by electrolytic reduction of their molten chlorides or oxides because these metals are not reduced by other reducing agents like coke, carbon monoxide etc.

Let us take an example of extraction of sodium metal. Sodium metal is extracted by electrolytic reduction of molten sodium chloride. On passing electricity through molten sodium chloride, decomposition reaction occurs and formation of sodium metal and chlorine gas takes place.

$2\mathrm{NaCl}\left(l\right)\stackrel{electrolysis}{\to }\mathrm{2Na}\left(s\right)+{\mathrm{Cl}}_2\left(g\right)$

Molten sodium chloride consists of sodium and chloride ions. The reactions that occurs during electrolysis are:

1. Cathode produces electrons to reduce sodium ions to sodium atoms (or sodium metal) by acting as a reducing agent. Sodium ions are cations; therefore, they get attracted to negatively charged cathode and get deposited there.
$$\begin{gathered} \mathrm{Cathode}:{\mathrm{2Na}}^{+}+{2e}^{-}\stackrel{}{\to }2Na \\ \mathrm{Sodium}\mathrm{ions}\mathrm{Electrons}\mathrm{Sodium}\mathrm{atoms} \\ (\mathrm{from}\mathrm{molten}\mathrm{NaCl})\mathrm{from}\mathrm{cathode}(\mathrm{or}\mathrm{sodium}\mathrm{metal}) \end{gathered}$$

2. Chloride ions, being anions, get attracted to positively charged anode. These chloride ions are oxidised to chlorine gas. Chlorine gas is produced at anode.

$$\begin{gathered} \mathrm{Anode}:{\mathrm{2Cl}}^{-}-{2e}^{-}\stackrel{}{\to }{\mathrm{Cl}}_2 \\ \mathrm{Chloride}\mathrm{ions}\mathrm{electrons}\mathrm{Chlorine}gas \\ (\mathrm{from}\mathrm{molten}\mathrm{NaCl})\mathrm{to}\mathrm{anode} \end{gathered}$$