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Electrolysis

A summary
by

Dr P.

on 13 February 2017

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Transcript of Electrolysis

Electrolyis
The breaking down of a substance using the passage of an electric current
Need ions which are free to move
Molten
Aqueous
positive ions go to negative electrode (CATHODE) and gain electrons (REDUCTION)
Negative ions go to positive electrode (ANODE) and lose electrons (OXIDATION)
Pb
2+
2e
-
Pb
+
2Cl
-
Cl
2
+
2e
-
ionic substances
Ionic substances
Water provided some extra ions!
H
OH
+
_
These ions also travel to oppositely charged electrodes and compete with the ions present from the ionic substance itself.
Reactive metal ions don't gain the electrons, the hydrogen ions get them.
2H
+
2e
H
2
-
+
Usually the hydroxide ions lose electrons and form oxygen
4OH
-
2H O + O + 4e
2
2
-
Specific examples
Brine
Concentrated sodium chloride solution
Purification of Copper
2Cl
-
Cl
2
+
2e
-
2H
+
2e
H
2
-
+
Na and OH ions remain
+
-
Electrolysis of an aqueous copper compound using copper electrodes
At negative electrode
At positive electrode
Cu + 2e
Cu
-
2+
copper IONS gain 2 electrons and form PURE copper
Copper ATOMS from the electrode LOSE electrons forming copper IONS
Cu
Cu
2+
+ 2e
-
Rich in other metals such as gold and silver
No overall change in copper ions in electrolyte
Metals above hydrogen in the reactivity series are never released during aqueous electrolysis.
Only metal ions below hydrogen in the reactivity series can gain electrons and be reduced to the metal in preference to hydrogen.
At the negative cathode
At the positive anode
Only when concentrated chloride, bromide, or iodide ions are present, does the halide ion lose electrons and the halogen is formed as the element.
2X
X + 2e
-
-
2
Full transcript