How is chlorine prepared by electrolytic method? Explain its reactions with
a) NaOH
b) NH₃ under different conditions

Principle: Brine solution is electrolysed
Manufacture:
1) Nelson cell contains ‘U’ shaped perforated steel vessel.
2) It acts as cathode
3) It is lined inside with asbestos
4) Brine solution is taken in the steel vessel
5) This vessel is suspended in a rectangular iron tank
6) Carbon rod is dipped in the brine solution which acts as anode
7) Steam is passed into the cell
8) On passing current chlorine gas is evolved and sodium ions diffuse through the asbestos and reach the cathode.
9) Steam reacts with Na+ ions to form NaOH
$2\mathrm{NaCl}\to 2{\mathrm{Na}}^{+}+2{\mathrm{Cl}}^{-}$
At Anode: $2{\mathrm{Cl}}^{-}\to {\mathrm{Cl}}_2+2{\mathrm{e}}^{-}$
At cathode : $2{\mathrm{H}}_2\mathrm{O}+2{\mathrm{e}}^{-}\to 2{\mathrm{OH}}^{-}+{\mathrm{H}}_2$
$2{\mathrm{Na}}^{+}+2{\mathrm{OH}}^{-}\to 2\mathrm{NaOH}$
Reaction with NH₃
i) Excess of chlorine reacts with NH3 to form NCl₃ & HCl
${\mathrm{NH}}_3+\underset{\left(\mathrm{excess}\right)}{3{\mathrm{Cl}}_2}\to {\mathrm{NCl}}_3+3\mathrm{HCl}$
ii) Excess of NH₃ reacts with chlorine to form nitrogen and ammonium chloride
$\underset{\left(\mathrm{excess}\right)}{8{\mathrm{NH}}_3}+3{\mathrm{Cl}}_2\to {\mathrm{N}}_2+6{\mathrm{NH}}_4\mathrm{Cl}$
Reaction with NaOH:
i) With cold and dilute NaOH it gives NaCl and NaOCl
$\underset{\mathrm{cold}}{2\mathrm{NaOH}}+{\mathrm{Cl}}_2\to \mathrm{NaCl}+\mathrm{NaClO}+{\mathrm{H}}_2\mathrm{O}$
ii) With hot conc.NaOH it gives NaCl and NaClO₃
$\underset{\mathrm{hot}}{6\mathrm{NaOH}}+3{\mathrm{Cl}}_2\to 5\mathrm{NaCl}+{\mathrm{NaClO}}_3+3{\mathrm{H}}_2\mathrm{O}$