The Alkali Metals - Group 1 - Electrolysis of Sodium Chloride in Water.
This page shows the electrolysis of sodium chloride
dissolved in water.
You get different products if the
sodium chloride is completely dry.
Sodium chloride
dissolved in water is called
brine.
Electrolysis of
brine gives hydrogen at the cathode and chlorine
at the anode.
You must know how to test for hydrogen and chlorine
gas.
Sodium hydroxide remains
dissolved in the solution.
This is an important industrial
process.
The reactions at each electrode are called half
equations.
The half equations are written so that
the same number of electrons
occur in each equation.
2H+ + 2e- 
H2 (hydrogen gas at the (-)cathode).
2Cl- -
2e-
Cl2
(chlorine gas at the (+)anode).
Hydrogen ions
gain
electrons (reduction) to form
hydrogen atoms.
The hydrogen atoms combine to form molecules of
hydrogen gas.
Chloride ions lose
electrons (oxidation) to form
chlorine atoms.
The chlorine atoms combine to form molecules of
chlorine gas.
The overall reaction is
2NaCl(aq) +
2H2O(l)
2Na+(aq)
+ 2OH-(aq)
+ Cl2(g)+
H2(g)
Electrolysis of hydrochloric
acid also gives
hydrogen at the cathode and chlorine
at the anode
but hydrochloric acid is more
expensive than brine
and you do not get sodium
hydroxide left in the solution.
(continued on the next page).
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