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.
0 comments :
Post a Comment