Electrolysis molten sodium chloride

1. ELECTROLYSIS MOLTEN SODIUM CHLORIDE
[Solid ionic compounds do not conduct electricity because their ions are held in
fixed positions by strong electrostatic forces]
[Aqueous electrolytes conduct electricity because their ions move freely]
a)Ions in the electrolyte are Sodium ions and Chloride ions
b)Sodium ions (Cations) are attracted to the cathode while Chloride ions
are attracted to the anode
c)Reaction at the cathode: Na
+
+ e Na
Explanation: Each sodium ion gains one electron to form sodium atom.
Sodium ions are discharged

Reaction at the anode: 2Cl
-
Cl2 + 2e
Explanation: Each chloride ion loses one electron to form chlorine atom.
Two chlorine atoms will combine to form Cl2 molecule
d)Observation
Cathode: Shiny silvery deposits are formed
Anode: greenish-yellow bubbles gas are eventually liberated
e)Overall reaction
2 Na
+
+ 2Cl
-
Cl2 + 2Na


ELECTROLYSIS OF AQUEOUS ELECTROLYTES
·Aqueous electrolytes are mixtures of two electrolytes – the compound and
water
·Water ionises to give H
+
and OH
-
as follows:
H2O H
+
+ OH
-
·More than one type of anion and cation are present
·Example: Electrolysis of dilute Sulphuric acid
H2SO4 2H
+
+ SO4
2-
H2O H
+
+ OH
-
·Sulphuric acid dissolves in water to form H
+
, SO4
2-
and OH
-
ions

2. a) Ions in the electrolyte: H
+
, SO4
2-
and OH
-
b) SO4
2-
and OH
-
ions migrate to the cathode while H
+
ions migrate to the
anode
c) Reaction at the cathode:
OH
-
ions are preferentially discharged
4OH
-
2H2O + O2 + 4e
Explaination: Each OH
-
ion loses one electron to form oxygen gas
and water.
Reaction at the anode:
2H
+
+ 2e H2
Explanation: Each H
+
ion gains one electron to form hydrogen atom.
Two hydrogen atoms will join together to form H2 molecule
d) Observation
Cathode: Colourless bubbles gas are formed
Validity test:
[To confirm the presence of gas is: place in the burning splinter into
the test tube, gas burns with a ‘pop’ sound]
Anode: Colourless bubbles are formed
Validity test:
[To confirm the presence of gas is: place in the glowing splinter into
the test tube, gas rekindles glowing splinter]