INDUSTRIAL PREPARATION OF SODIUM HYDROXIDE
 
SODIUM HYDROXIDE
 
    Chemical formula : NaOH
    Chemical name : sodium hydroxide
    Commercial name : caustic soda
RAW MATERIALS USED
IN THE PREPARATION
 
    Sodium chloride (NaCl).
    Water (H2O).
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PRINICIPLE
 
    Sodium hydroxide is a strong base and is prepared by the electrolysis of aqueous solution of sodium     chloride known as brine.
METHOD
 
    PREPARATION OF BRINE:
    NaCl is mixed in water to produce brine. Composition of brine is 25% m/m.
ELECTROLYSIS OF BRINE
 
    Electrolysis of brine is carried out in an electrolytic cell known as "Diaphragm cell". When an electric     current is passed through the brine, following changes take place.
    Ionization of NaCl:           2NaCl ® 2Na+ + 2Cl-
    Ionization H2O:               2H2O ® 2H+ + 2OH-
    Electrochemical changes
 
    At cathode:              2H+ + 2e- ® H2
    At anode:                  2Cl- ®Cl2 + 2e-
    During electrolysis, Na+ ions are not discharged but H+ ions are readily discharged. As more H+ ions     are discharged, more H2O dissociates to replace it. Na+ and OH- ions accumulate in the solution. On     evaporation sodium hydroxide is obtained.
                                Na+ + OH- ® NaOH
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