Caustic Soda Or NaOH (Castner Kellner's Process)

Caustic Soda Or NaOH (Castner Kellner's Process)

2nd Year Chemistry Notes

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Caustic Soda Or NaOH (Castner Kellner's Process)



Introduction



Caustic Soda or Sodium Hydroxide is one of the most important chemicals
of industrial use. Caustic Soda must be handled carefully because it is
caustic to touch and causes painful burns.





Castner Kellner's Process



Caustic Soda is manufacture by an electrolytic process. This process is
carried out in an electrolytic cell known as Castner-Kellner's cell and
the process is called Castner-Kellner's Process.





Construction Of Castner-Kellner's Cell



The electrolytic solution is a 25% of NaCl solution. The anode consist
of a number of titanium plates whereas cathode is a steam of flowing
mercury.

Diagram Coming Soon





Working of Castner-Kellner's Cell



Sodium chloride dissociates in water to give Na+ and Cl- ions are



2NaCl ----> 2Na+ + 2Cl-



The Cl- ions migrate towards titanium plates, it gains electron and convert into chlorine gas.



2Cl- ----> Cl2 + 2e- (Oxidation)



In castner-kellner's process, H+ ions are not easily discharged due to
high voltage of H+ ions, on the contrary Na+ ions are easily discharge
over mercury surface. The sodium, thus liberated dissolves in mercury
forming an amalgam.



2Na+ + 2e- ----> 2Na (Reduction)



Na + Hg ----> Na/Hg (Amalgum)'



The mercury containing dissolved sodium is sent to another chamber
called Denuder where sodium reacts with water forming sodium hydroxide
and hydrogen. Denuder is packed with graphite blocks as hydrogen is
easily liberated over graphite surface.



2Na/Hg + 2H2O ----> 2NaOH + H2 + 2Hg



The mercury is recycled to dissolve more of sodium.



The solution, which flows out from denuder, is a NaOH solution, which is evaporated to dryness