Wednesday, 21 January 2015

6.4 Electrolysis in industry

Uses of electrolysis in industry
■ Uses of electrolysis in industry

The extraction of metals

The purification of metals

Electroplating of metals
Extraction of metals
■ Extraction of metals

Electrolysis can be used to extract metals from their ores.

Used to extract metals that are more reactive than carbon - potassium, sodium, calcium, magnesium and aluminium.
■ Extraction of aluminium

Extract from its ore, bauxite, which contains aluminium oxide(Al2O3)

Molten aluminium oxide is mixed with crylolite to lower its melting point.

Electrolysed by using carbon electrodes.

Electrolyte: molten aluminium oxide At anode(+) At cathode(-)
Ions present O2- Al3+
Ion selected for discharged Ion O2- selected for discharged Ion Al3+ selected for discharged
Half-equation O2- → O2 + 4e-
Oxygen gas is collected
Al3+ + 3e- → Al
Aluminium is produced
■ This video shows the processes of bauxite extraction.


Purification of metals
■ Purification of metals

Electrolysis can be used to purify the impure metal.

Cathode : pure metal, anode : impure metal

Electrolyte : a salt containing the ions of the metal being purified.
■ Purification of copper


Electrolyte: Copper(II) Sulphate solution At anode(+) [Impure copper] At cathode(-) [Pure copper]
Ions present SO42-, OH- Cu2+, H+
Ion selected for discharged Copper electrode ionizes to form ion Cu2+ Ion Cu2+ selected for discharged as it is lower position in electrochemical series.
Half-equation Cu → Cu2+ + 2e-
Copper electrode dissolve and its weight decrease.
Cu2+ + 2e- → Cu
Copper metal is deposited

The impurities form a deposit below the anode.
■ This video shows the electrolytic refining of copper in an animated series.


Electroplating of metals
■ Electroplating of metals

Electrolysis can be used to put a metallic coating on an object.

Cathode : object to be plated, anode : metal that is used to plate the object.

Electrolyte : a salt containing the ions of the metal used as anode.
■ Electroplating of metal spoon with silver


Electrolyte: Silver Sulphate solution At anode(+) [Silver] At cathode(-) [Spoon]
Ions present SO42-, OH- Ag+, H+
Ion selected for discharged Silver electrode ionizes to form ion Ag+ Ion Ag+ selected for discharged as it is lower position in electrochemical series.
Half-equation Ag → Ag+ + e-
Silver is deposited on the electrode and its weight increase.
Ag+ + e- → Ag
Silver metal is deposited. A thin silver layer forms on the spoon
■ This video shows the electroplating of coin with nickel and copper.




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