The Periodic Table
The Alkali Metals - Electrolysis of Sodium Chloride in Water.
This page shows the electrolysis of sodium chloride
which has been dissolved in water. You get
different products if the sodium chloride is completely dry.
What is the Electrolysis of Brine?
dissolved in water is called
Electrolysis of brine gives hydrogen gas at the cathode and
chlorine gas at the anode. You must know how to test
for hydrogen and chlorine gas. Sodium hydroxide remains
dissolved in the solution. The picture below shows
what happens to the ions during the electrolysis of brine.
This is an important industrial process making
hydrogen gas, chlorine gas and sodium hydroxide.
What are Half Equations?
The reactions at each electrode are called half
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).
electrons (reduction) to form
The hydrogen atoms combine to form molecules of hydrogen gas.
Chloride ions lose
electrons (oxidation) to form
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.
See more detail of the electrolysis on the next page.
Links Alkali Metals Revision Questions
gcsescience.com The Periodic Table Index Periodic Table Quiz gcsescience.com
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