(i) Sodium metal is prepared by electrolysis of fused NaCl at 873 K using iron cathode and graphite anode (Down’s cell). NaCl ⇌ $\mathrm{Na}^+ + \mathrm{Cl}^-$ At anode : $2\mathrm{Cl}^-$ → $2\mathrm{Cl} + 2\mathrm{e}^-$ → $\mathrm{Cl}_2$ At cathode : $\mathrm{Na}^+ + \mathrm{e}^-$ → Na (ii) Sodium hydroxide is prepared by electrolysis of aqueous solution of NaCl using Hg cathode and carbon anode. (Castner-Kellner cell) : NaCl ⇌ $\mathrm{Na}^+ + \mathrm{Cl}^-$ At cathode : $\mathrm{Na}^+ + \mathrm{e}^-$ $\xrightarrow[\mathrm{Hg}]{}$ Na-amalgam At anode : $\mathrm{Cl}^-$ → $\frac{1}{2}\mathrm{Cl}_2 + \mathrm{e}^-$ Na - amalgam is treated with water to give NaOH and $\mathrm{H}_2$ : 2Na-amalgam + $2\mathrm{H}_2\mathrm{O}$ → $2\mathrm{NaOH} + 2\mathrm{Hg} + \mathrm{H}_2$ (iii) Sodium chloride to sodium peroxide : NaCl ⇌ $\mathrm{Na}^+ + \mathrm{Cl}^-$ At anode : $2\mathrm{Cl}^-$ → $2\mathrm{Cl} + 2\mathrm{e}^-$ → $\mathrm{Cl}_2$ At cathode : $\mathrm{Na}^+ + \mathrm{e}^-$ → Na Sodium is heated in excess of air. 2Na + $\mathrm{O}_2 \xrightarrow{\Delta} \mathrm{Na}_2\mathrm{O}_2$. (iv) Sodium hydrogen carbonate is prepared by passing $\mathrm{CO}_2$ through NaCl solution saturated with $\mathrm{NH}_3 \cdot \mathrm{NaHCO}_3$ formed is heated to give $\mathrm{Na}_2\mathrm{CO}_3$. (Solvay process) : $\mathrm{NH}_3 + \mathrm{H}_2\mathrm{O} + \mathrm{CO}_2$ + NaCl → $\mathrm{NaHCO}_3 + \mathrm{NH}_4\mathrm{Cl}$ 2NaHCO3 Na2CO3 + H2O + CO2