What happens.at cathode and anode during electrolytic reduction of sodium.chloride
Dear student,
Electrolysis of molten sodium chloride yields sodium metal and chloride gas.
Electrolytic cell consists of a rectangular container of steel tank, whose inside are lined with firebricks.
Anode is a graphite rod and cathode is a ring of iron, which surrounds the anode.
The anode and cathode are separated from each other by cylindrical steel gauze, so that Na and Cl2 are kept apart.
Melting point of NaCl is 801C. At this temperature molten NaCl and Na form a metallic fog in the container which is impossible to separate. In order to over come this difficulty instead of only NaCl, a mixture of NaCl and CaCl2 is electrolyzed in down's cell. The melting point of this mixture is 600C. At 600C no metallic fog is formed.
Composition:
NaCl = 42%
CaCl2 = 58%
Reactions which takes place:
Fused NaCl contains sodium and chloride ions.
2NaCl ----------> 2Na+ + 2Cl-
At cathode
Na+ ions migrate to cathode where they are reduced to Na.
2Na+ + 2e- --------> 2Na (Reduction)
At anode
Cl- ions migrate to anode and oxidised to form chlorine gas.
2Cl- -----------> Cl2 + 2e- (Oxidation)
Overall Reaction
2Na+ + 2e- ---------> 2Na
2Cl- -----------> Cl2 + 2e-
__________________________
2Na+ + 2Cl- ----------> 2Na + Cl2
During electrolysis calcium is also obtained at cathode but sodium and calcium are separated from each other due difference in density. Density of Na is 0.67gm/cc and the density of Ca is much higher than that of Na i.e. 2.54gm/cc. That's why they do not mix with each other.
Regards
Dear student,
Electrolysis of molten sodium chloride yields sodium metal and chloride gas.
Electrolytic cell consists of a rectangular container of steel tank, whose inside are lined with firebricks.
Anode is a graphite rod and cathode is a ring of iron, which surrounds the anode.
The anode and cathode are separated from each other by cylindrical steel gauze, so that Na and Cl2 are kept apart.
Melting point of NaCl is 801C. At this temperature molten NaCl and Na form a metallic fog in the container which is impossible to separate. In order to over come this difficulty instead of only NaCl, a mixture of NaCl and CaCl2 is electrolyzed in down's cell. The melting point of this mixture is 600C. At 600C no metallic fog is formed.
Composition:
NaCl = 42%
CaCl2 = 58%
Reactions which takes place:
Fused NaCl contains sodium and chloride ions.
2NaCl ----------> 2Na+ + 2Cl-
At cathode
Na+ ions migrate to cathode where they are reduced to Na.
2Na+ + 2e- --------> 2Na (Reduction)
At anode
Cl- ions migrate to anode and oxidised to form chlorine gas.
2Cl- -----------> Cl2 + 2e- (Oxidation)
Overall Reaction
2Na+ + 2e- ---------> 2Na
2Cl- -----------> Cl2 + 2e-
__________________________
2Na+ + 2Cl- ----------> 2Na + Cl2
During electrolysis calcium is also obtained at cathode but sodium and calcium are separated from each other due difference in density. Density of Na is 0.67gm/cc and the density of Ca is much higher than that of Na i.e. 2.54gm/cc. That's why they do not mix with each other.
Regards
