Extraction of Metals

What is Electrolysis?

Electrolysis is the name of the process where an electric current
is passed through a liquid that conducts electricity.

Very pure water will not conduct electricity
but water with a small level of impurities will conduct
and the water is decomposed into hydrogen gas and oxygen gas.

The elements in ionic compounds can be separated by electrolysis.

Metals above carbon in the reactivity series
(potassium, sodium, lithium, calcium, magnesium and aluminium)
are extracted by electrolysis.
Extraction from the metal ore involves reduction of the metal,
and electrons can reduce any metal ion.

metal ions  +  electrons    arrow   metal  atoms  (reduction).
non-metal ions  -  electrons    arrow    non-metal atoms (oxidation).


The electrodes are often made from graphite.
The liquid which conducts electricity is called the electrolyte.
The amount of electricity needed to produce a particular mass
of metal (or non-metal) can be calculated.

The negative electrode, called the cathode,
will attract positively charged metal ions.
The metal ions collect electrons from the cathode
and are discharged as metal atoms.

The positive electrode, called the anode,
will attract negatively charged non-metal ions.
The non-metal ions lose electrons to the anode
and are discharged as non-metal atoms.

For example, see lead bromide, magnesium chloride,
potassium chloride, sodium chloride and zinc chloride.
Electrolysis can also be used for metal plating.

Metals below carbon in the reactivity series are reduced by
heating with carbon because this is cheaper than electrolysis.

Metals above carbon in the reactivity series could be reduced
by reaction with a more reactive metal
but this is more expensive than electrolysis, and is
only used on a commercial scale for the extraction of titanium.

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